air tanah dan tanaman

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1 AIR TANAH & TANAMAN MK. TANAH & Media Tumbuh Tanaman d) Besar Kecilnya Pot

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Page 1: Air Tanah Dan Tanaman

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AIR TANAH&

TANAMAN

(Prof.Dr.Ir.Soemarno, M.S.)Oktober 2008

MK. TANAH & Media Tumbuh Tanaman

d) Besar Kecilnya Pot

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Proses fotosintesis memerlukan air

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Air dari tanah

CO2 dari Udara

Fotosintesis:CO2 + H2O ---- Karbohidrat

(Glukosa)

Glukosa Pati

dan senyawa organik lain dalam buah dan biji

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Stomata:

Pintu lalulintas CO2, O2, dan H2O

Fotosintesis:CO2 + H2O Karbohidrat

(Glukosa)

CO2 dari Udara

Glukosa Pati

dan senyawa organik lain dalam biji

Air dari tanah

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Budidaya tanaman padi sawah

memerlukan banyak air

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Kurva Penggunaan Air Musiman oleh Tanaman

KEBUTUHAN AIR TANAMAN

A plant has different water needs at different stages of growth. While

a plant is young it requires less water than

when it is in the reproductive stage.

When the plant approaches maturity, its

water need drops. Curves have been

developed that show the daily water needs for most types of crops.

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KEDALAMAN PERAKARAN TANAMAN

A plant’s root depth determines the depth to which soil water can be extracted. A young plant has only shallow roots and soil water deeper

than rooting depth is of no use to the plant. Plants typically extract about 40 percent of their water needs from the top quarter of their

root zone, then 30 percent from the next quarter, 20 percent from the third quarter, taking only 10 percent from the deepest quarter.

Therefore, plants will extract about 70 percent of their water from the top half of their total root penetration.

Deeper portions of the root zone can supply a higher percentage of the crop’s water needs if the upper portion is depleted. However, reliance on utilization of deeper water will reduce optimum plant

growth.

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KUALITAS AIR & TANAH

For good plant growth, a soil must have adequate room for water and air movement, and for root growth. A soil’s structure can be

altered by certain soil management practices. For example, excessive tillage can break apart aggregated soil and excessive traffic can cause compaction. Both of these practices reduce the amount of pore space

in the soil, and thus reduce the availability of water and air, and reduce the room for root development.

Irrigation water with a high content of soluble salt is not as available to the plant, so a higher soil water content must be maintained in

order to have water available to the plant. Increasing salt content of the water reduces the potential to move water from the soil to the

roots. Some additional water would also be needed to leach the salt below the crop root zone to revent build-up in the soil. Poor quality

water can affect soil structure.

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Kebutuhan air BAWANG PUTIH (Allium cepa)

Untuk mencapai hasuil optimum tanaman onion memerlukan 350-550 mm air. Tanaman sangat peka terhadap kondisi defisit air tanah. Untuk mencapai hasil yang tinggi, penurunan kandungan air tanah tidak boleh melebihi 25% air tanah tersedia.

Tanaman paling peka terhadap defisit air selama periode pembentukan umbi, terutama selama periode pertumbuhan umbi yang cepat yang terjadi sekitar 60 hari

setelah transplanting. Tanaman juga sangat peka kekeringan selama masa transplantasi. Selama periode pertumbuhan vegetatif tanaman agak kurang peka

terhadap defisit air tanah. Untuk mendapatkan hasil yang banyak dan kualitas yang baik, tanaman memerlukan suplai air yang terkendali dan sering selama musim

pertumbuhannya; akan tetapi irigasi yang berlebihan mengakibatkan pertumbuhan terhambat.

Untuk mendapatkan ukuran umbi yang besar dan bobot yang tinggi, defisit air tanah terutama selama periode pembentukan hasil (Periode pembesaran umbi) tidak

boleh terjadi. Kalau supali air terbatas, maka penghematan air dapat dilakukan selama periode pertumbuhan vegetatif dan periode pemasakan.

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Komposisi tana menurut volume

Tanah subur yg ideal:• Mineral 45%• Organic matter 5%• Water 25%• Air 25%

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Tiga komponen tanah

The soil system is composed of three major components: solid particles (minerals and organic matter), water with various

dissolved chemicals, and air.

The percentage of these components varies greatly with soil texture and structure.

An active root system requires a delicate balance between the three soil components; but the balance between the liquid and gas phases

is most critical, since it regulates root activity and plant growth process.

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A soil profile is the sequence of natural layers, or horizons,

in a soil. Each soil series consists of soils having major

horizons that are similar in color, texture, structure,

reaction, consistency, mineral and chemical composition, and arrangement in the soil

profile. The soil profile extends from the surface

downward to unconsolidated material. Most soils have three

major horizons called the surface horizon, the subsoil,

and the substratum.

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STRUKTUR & CIRI H2O

Molekul air terdiri atas atom oksigen dan dua atom hidrogen, yang berikatan secara kovalenAtom-atom tidak terikat secara linear (H-O-H), tetapi atom hidrogen melekat pada atom oksigen seperti huruf V dengan sudut 105o.

Molekul air bersifat dipolar: Zone elektro positif

+

H H 105o

Zone elektro negatif

-

Page 16: Air Tanah Dan Tanaman

16Ilustrasi tentang penurunan potensial air untuk suatu tanaman

Plants develop the tension, or potential, to move soil water

from the soil intothe roots and distribute the water through the plant by

adjusting the water potential, or tension, within their plant

cells.

The essence of the process is that water always moves

from higher to lower water potential.

For water to move from the soil, to roots, to stems, to leaves, to air the water

potential must always be decreasing.

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Lingkaran Tanah-Air-Tanaman

LTAT mrpk sistem dinamik dan terpadu dimana air mengalir dari tempat dengan tegangan rendah menuju tempat dengan

tegangan air tinggi.

Serapan bulu akarPenguapan

Hilang melalui stomata daun (transpirasi)

Air kembali ke atmosfer

(evapo-transpirasi)

Air dikembalikan ke tanah melalui hujan

dan irigasi

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SISTEM TANAH-TANAMAN

Structure of water transport model for the soil-leaf continuum, with the inputs outlined in boxes.

Root and shoot components are represented by a resistance network, each component of which varies according to the inputted K(y)

function from vulnerability curves of xylem.

Layers of roots reach to different soil depths according to an inputted root area profile. Canopy layers reflect an inputted leaf area and Y

profile.

Soil is modeled as a rhizosphere resistance connecting roots to bulk soil of an inputted y and K(y).

The model predicts transpiration (E) as a function of the inputs.

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Model struktur sistem tanaman dalam konteks hubungan Air-Tanah-Tanaman

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Kekuatan ikatan antara molekul air dengan partikel tanah dinyatakan dengan TEGANGAN AIR TANAH. Ini merupakan fungsi dari gaya-gaya adesi dan kohesi di antara molekul - molekul air dan

partikel tanah

Partikel tanah

H2O

Adesi Kohesi

Air terikat Air bebas

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Air Tersedia untuk pertumbuhan tanaman

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).

Fine textured soils with small pores can hold the greatest

amounts of PAW.

Coarse textured sandy soils with large pores can hold the least

amounts of PAW.

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Status Air Tanah

Perubahan status air dalam tanah, mulai dari kondisi jenuh hingga titik layu

Jenuh Kap. Lapang Titik layu

100g 8g udara

Padatan Pori

100g 20g udara

100g 10 g udara

100g air 40g tanah jenuh air

kapasitas lapang

koefisien layu

koefisien higroskopis

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TEGANGAN &

KADAR AIR

PERHATIKANLAH proses yang terjadi kalau tanah basah dibiarkan mengering. Bagan berikut melukiskan hubungan antara tebal lapisan air di sekeliling partikel tanah dengan tegangan air

Bidang singgung tanah dan air Koef. Koef. Kapasitaspadatan tanah higroskopis layu lapang

10.000 atm 31 atm 15 atm 1/3 atm

10.000 atm Mengalir krn gravitasi

Tegangan air

1/3 atm

tebal lapisan air

Page 25: Air Tanah Dan Tanaman

25Representasi bola air yang menyelubungi partikel padatan tanah

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JUMLAH AIR DALAM TANAH

The amount of soil water is usually measured in terms of water content as percentage by volume or mass, or as soil water potential. Water content does

not necessarily describe the availability of the water to the plants, nor indicates, how the water moves within the soil profile. The only information provided by

water content is the relative amount of water in the soil.

Soil water potential, which is defined as the energy required to remove water from the soil, does not directly give the amount of water present in the root

zone either. Therefore, soil water content and soil water potential should both be considered when dealing with plant growth and irrigation.

The soil water content and soil water potential are related to each other, and

the soil water characteristic curve provides a graphical representation of this relationship.

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TEGANGAN vs

kadar air

Kurva tegangan - kadar air tanah bertekstur lempung

Tegangan air, bar

31 Koefisien higroskopis

Koefisien layu

Kapasitas lapang 0.1 Kap. Lapang maksimum

persen air tanah

Air kapilerAir Air tersediahigros-kopis Lambat tersedia Cepat tersedia Air gravitasi

Zone optimum

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Hubungan antara kadar air tanah dan tegangan air tanah untuk tekstur lempung

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STRUKTUR &

CIRI

POLARITASMolekul air mempunyai dua ujung, yaitu ujung oksigen yg elektronegatif dan ujung hidrogen yang elektro-positif.Dalam kondisi cair, molekul-molekul air saling bergandengan membentuk kelompok-kelompok kecil tdk teratur.Ciri polaritas ini menyebabkan plekul air tertarik pada ion-ion elektrostatis. Kation-kation K+, Na+, Ca++ menjadi berhidrasi kalau ada molekul air, membentuk selimut air, ujung negatif melekat kation.Permukaan liat yang bermuatan negatif, menarik ujung positif molekul air.

Kation hidrasi Tebalnya selubung air tgtpd rapat muatan pd per-mukaan kation.

Rapat muatan = Selubung air muatan kation / luas permukaan

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STRUKTUR &

CIRI

IKATAN HIDROGEN Atom hidrogen berfungsi sebagai titik penyambung (jembatan) antar molekul air.Ikatan hidrogen inilah yg menyebabkan titik didih dan viskositas air relatif tinggi

KOHESI vs. ADHESIKohesi: ikatan hidrogen antar molekul airAdhesi: ikatan antara molekul air dengan permukaan padatan lainnyaMelalui kedua gaya-gaya ini partikel tanah mampu menahan air dan mengendalikan gerakannya dalam tanah

TEGANGAN PERMUKAAN Terjadinya pada bidang persentuhan air dan udara, gaya kohesi antar molekul air lebih besra daripada adhesi antara air dan udara.

UdaraPermukaan air-udara

air

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ENERGI AIR TANAH

Retensi dan pergerakan air tanah melibatkan energi, yaitu: Energi Potensial, Energi Kinetik dan Energi Elektrik.Selanjutnya status energi dari air disebut ENERGI BEBAS, yang merupakan PENJUMLAHAN dari SEMUA BENTUK ENERGI yang ada.Air bergerak dari zone air berenergi bebas tinggi (tanah basah) menuju zone air berenergi bebas rendah (tanah kering).

Gaya-gaya yg berpengaruhGaya matrik: tarikan padatan tanah (matrik) thd molekul air; Gaya osmotik: tarikan kation-kation terlarut thd molekul airGaya gravitasi: tarikan bumi terhadap molekul air tanah.

Potensial air tanahKetiga gaya tersebut di atas bekerja bersama mempengaruhi energi bebas air tanah, dan selanjutnya menentukan perilaku air tanah, ….. POTENSIAL TOTAL AIR TANAH (PTAT)PTAT adalah jumlah kerja yg harus dilakukan untuk memindahkan secara berlawanan arah sejumlah air murni bebas dari ketinggian tertentu secara isotermik ke posisi tertentu air tanah.PTAT = Pt = perbedaan antara status energi air tanah dan air murni bebas

Pt = Pg + Pm + Po + …………………………

( t = total; g = gravitasi; m = matrik; o = osmotik)

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Hubungan potensial air tanah dengan energi bebas

Energi bebas naik bila air tanah berada pada letak ketinggian yg lebih tinggi dari titik baku pengenal (referensi)

+

0

-

Poten-sial

positif

Poten-sial

negatif

Energi bebas dari air murni Potensial tarikan bumi

Menurun karena pengaruh osmotik

Menurun karena pengaruh matrik

Energi bebas dari air tanah

Potensial osmotik (hisapan)

Potensial matrik (hisapan)

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POTENSIAL AIR TANAH

POTENSIAL TARIKAN BUMI = Potensial gravitasi

Pg = G.hdimana G = percepatan gravitasi, h = tinggi air tanah di atas posisi ketinggian referensi.Potensial gravitasi berperanan penting dalam menghilangkan kelebihan air dari bagian atas zone perakaran setelah hujan lebat atau irigasi

Potensial matrik dan OsmotikPotensial matrik merupakan hasil dari gaya-gaya jerapan dan kapilaritas.Gaya jerapan ditentukan oleh tarikan air oleh padatan tanah dan kation jerapanGaya kapilaritas disebabkan oleh adanya tegangan permukaan air.Potensial matriks selalu negatifPotensial osmotik terdapat pd larutan tanah, disebabkan oleh adanya bahan-bahan terlarut (ionik dan non-ionik).Pengaruh utama potensial osmotik adalah pada serapan air oleh tanaman

Hisapan dan Tegangan Potensial matrik dan osmotik adalah negatif, keduanya bersifat menurunkan energi bebas air tanah. Oleh karena itu seringkali potensial negatif itu disebut HISAPAN atau TEGANGAN.Hisapan atau Tegangan dapat dinyatakan dengan satuan-satuan positif.Jadi padatan-tanah bertanggung jawab atas munculnya HISAPAN atau TEGANGAN.

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Cara Menyatakan

Tegangan Energi

Tegangan: dinyatakan dengan “tinggi (cm) dari satuan kolom air yang bobotnya sama dengan

tegangan tsb”.Tinggi kolom air (cm) tersebut lazimnya

dikonversi menjadi logaritma dari sentimeter tinggi kolom air, selanjutnya disebut pF.

Tinggi unit Logaritma Bar Atmosferkolom air (cm) tinggi kolom air (pF)

10 1 0.01 0.0097 100 2 0.1 0.0967 346 2.53 0.346 1.3 1000 3 110000 4 10 9.674915849 4.18 15.8 1531623 4.5 31.6 31100.000 5 100 96.7492

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KANDUNGAN AIR DAN

TEGANGAN

KURVA ENERGI - LENGAS TANAH Tegangan air menurun secara gradual dengan meningkatnya kadar air tanah.Tanah liat menahan air lebih banyak dibanding tanah pasir pada nilai tegangan air yang samaTanah yang Strukturnya baik mempunyai total pori lebih banyak, shg mampu menahan air lebih banyakPori medium dan mikro lebih kuat menahan air dp pori makro

Tegangan air tanah, Bar 10.000

Liat

Lempung

Pasir

0.0110 Kadar air tanah, % 70

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Tekstur tanah dan air tersedia

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Hubungan antara kadar air tanah dengan tegangan air tanah

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38Jelaskan bagaimana tektur tanah mempengaruhi jumlah air tersedia bagi

tanaman? Sebanyak 250 kata

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Jelaskan tanah-tanah yang tekturnya halus mampu menahan lebih banyak air dibandingkan dgn tanah-tanah yang teksturnya kasar? Sebanyak 250 kata

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Kapasitas air tersedia dalam tanah yang teksturnya berbeda-beda

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Gerakan Air Tanah

Tidak Jenuh

Gerakan tidak jenuh = gejala kapilaritas = air bergerak dari muka air tanah ke atas melalui pori mikro.Gaya adhesi dan kohesi bekerja aktif pada kolom air (dalam pri mikro), ujung kolom air berbentuk cekung.Perbedaan tegangan air tanah akan menentukan arah gerakan air tanah secara tidak jenuh.

Air bergerak dari daerah dengan tegangan rendah (kadar air tinggi) ke daerah yang tegangannya tinggi (kadar air rendah, kering).Gerakan air ini dapat terjadi ke segala arah dan berlangsung secara terus-menerus.

Pelapisan tanah berpengaruh terhadap gerakan air tanah.Lapisan keras atau lapisan kedap air memperlambat gerakan air Lapisan berpasir menjadi penghalang bagi gerakan air dari lapisan yg bertekstur halus.Gerakan air dlm lapisan berpasir sgt lambat pd tegangan

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Gerakan Jenuh (Perkolasi)

Air hujan dan irigasi memasuki tanah, menggantikan udara dalam pori makro - medium - mikro. Selanjutnya air bergerak ke bawah melalui proses gerakan jenuh dibawah pengaruh gaya gravitasi dan kapiler.Gerakan air jenuh ke arah bawah ini berlangsung terus selama cukup air dan tidak ada lapisan penghalang

Lempung berpasir Lempung berliat

cm 0

15 mnt 4 jam 30 60

90 1 jam 24 jam

120 24 jam 48 jam

150 30 cm 60 cm Jarak dari tengah-tengah saluran, cm

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Pola Penetrasi dan Pergerakan Air pada tanah Berpasir dan tanah Lempung-liat

Page 44: Air Tanah Dan Tanaman

44Pola pergerakan air gravitasi dalam tanah

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Pengaruh struktur tanah terhadap pergerakan air tanah ke arah bawah

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PERKOLASI

Jumlah air perkolasiFaktor yg berpengaruh:

1. Jumlah air yang ditambahkan2. Kemampuan infiltrasi permukaan tanah3. Daya hantar air horison tanah4. Jumlah air yg ditahan profil tanah pd kondisi kapasitas lapang

Keempat faktor di atas ditentukan oleh struktur dan tekstur tanah

Tanah berpasir punya kapasitas ilfiltrasi dan daya hantar air sangat tinggi, kemampuan menahan air rendah, shg perkolasinya mudah dan cepat

Tanah tekstur halus, umumnya perkolasinya rendah dan sangat beragam; faktor lain yg berpengaruh:1. Bahan liat koloidal dpt menyumbat pori mikro & medium2. Liat tipe 2:1 yang mengembang-mengkerut sangat berperan

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LAJU GERAKAN

AIR TANAH

Kecepatan gerakan air dlm tanah dipengaruhi oleh dua faktor:1. Daya dari air yang bergerak2. Hantaran hidraulik = Hantaran kapiler = daya hantar

i = k.fdimana i = volume air yang bergerak; f = daya air yg bergerak dan k = konstante.

Daya air yg bergerak = daya penggerak, ditentukan oleh dua faktor:1. Gaya gravitasi, berpengaruh thd gerak ke bawah2. Selisih tegangan air tanah, ke semua arah

Gerakan air semakin cepat kalau perbedaan tegangan semakin tinggi.

Hantaran hidraulik ditentukan oleh bbrp faktor:1. Ukuran pori tanah2. Besarnya tegangan untuk menahan air

Pada gerakan jenuh, tegangan airnya rendah, shg hantaran hidraulik berbanding lurus dengan ukuran poriPd tanah pasir, penurunan daya hantar lebih jelas kalau terjadi penurunan kandungan air tanahLapisan pasir dlm profil tanah akan menjadi penghalang gerakan air tidak jenuh

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Gerakan air tanah

Gerakan air tanah dipengaruhi oleh kandungan air tanah

Penetrasi air dari tnh basah ke tnh kering(cm) 18

Tanah lembab, kadar air awal 29%

Tanah lembab, kadar air awal 20.2%

Tanah lembab, kadar air awal 15.9%

0 26 156

Jumlah hari kontak, hari

Sumber: Gardner & Widtsoe, 1921.

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GERAKAN UAP AIR

Penguapan air tanah terjadi internal (dalam pori tanah) dan eksternal (di permukaan tanah)Udara tanah selalu jenus uap air, selama kadar air tanah tidak lebih rendah dari koefisien higroskopis (tegangan 31 atm).

Mekanisme Gerakan uap airDifusi uap air terjadi dlm udara tanah, penggeraknya adalah perbedaan tekanan uap air.Arah gerapan menuju ke daerah dg tekanan uap rendah

Pengaruh suhu dan lengas tanah terhadap gerapan uap air dalam tanah

Lembab Dingin Kering Dingin

Kering Panas Lembab Panas

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RETENSI AIR TANAH

KAPASITAS RETENSI MAKSIMUM adalah: Kondisi tanah pada saat semua pori terisi penuh air, tanah jenuh air, dan tegangan matrik adalah nol.KAPASITAS LAPANG: air telah meninggalkan pori makro, mori makro berisi udara, pori mikro masih berisi air; tegangan matrik 0.1 - 0.2 bar; pergerakan air terjadi pd pori mikro/ kapiler

KOEFISIEN LAYU: siang hari tanaman layu dan malam hari segar kembali, lama-lama tanaman layu siang dan malam; tegangan matrik 15 bar.Air tanah hanya mengisi pori mikro yang terkecil saja, sebagian besar air tidak tersedia bagi tanaman.Titik layu permanen, bila tanaman tidak dapat segar kembali

KOEFISIEN HIGROSKOPISMolekul air terikat pada permukaan partikel koloid tanah, terikat kuat sehingga tidak berupa cairan, dan hanya dapat bergerak dlm bentuk uap air, tegangan matrik-nya sekitar 31 bar.Tanah yg kaya bahan koloid akan mampu menahan air higroskopis lebih banyak dp tanah yg miskin bahan koloidal.

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Klasifikasi Air Tanah

Klasifikasi Fisik:1. Air Bebas (drainase)2. Air Kapiler3. Air Higroskopis

Air Bebas (Drainase):a. Air yang berada di atas kapasitas lapangb. Air yang ditahan tanah dg tegangan kurang dari 0.1-0.5 atmc. Tidak diinginkan, hilang dengan drainased. Bergerak sebagai respon thd tegangan dan tarika gravitasi bumie. Hara tercuci bersamanya

AIR KAPILER: a. Air antara kapasitas lapang dan koefisien higroskopisb. Tegangan lapisan air berkisar 0.1 - 31 atmc. Tidak semuanya tersedia bagi tanamand. Bergerak dari lapisan tebal ke lapisan tipise. Berfungsi sebagai larutan tanah

AIR HIGROSKOPIS : a. Air diikat pd koefisien higroskopisb. Tegangan berkisar antara 31 - 10.000 atmc. Diikat oleh koloid tanahd. Sebagian besar bersifat non-cairane. Bergerak sebagai uap air

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Agihan air dalam tanah

Berdasarkan tegangan air tanah dapat dibedakan menjadi tiga bagian: Air bebas, kapiler dan higroskopis

Koef. Higroskopis Kap. Lapang Jml ruang pori kurang lebih 31 atm kurang lebih 1/3 atm

Lapisan olah

Air higros- Air Kapiler Ruang diisi udara kopik Peka thd gerakan Biasanya jenuh uap air Hampir tdk kapiler, laju pe- Setelah hujan lebat menunjukkan nyesuaian me- sebagian diisi air, sifat cairan ningkat dg me- tetapi air cepat hi- ningkatnya ke- lang krn gravitasi lembaban tanah bumi Lapisan bawah tanah

Karena pemadatan ruang pori berkurang

Strata bawah (jenuh air)

Kolom tanah Jumlah ruang pori

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Klasifikasi Biologi

Air tanah

Klasifikasi berdasarkan ketersediaannya bagi tanaman:1. AIR BERLEBIHAN: air bebas yg kurang tersedia bagi tanaman.

Kalau jumlahnya banyak berdampak buruk bagi tanaman, aerasi buruk, akar kekurangan oksigen, anaerobik, pencucian air

2. AIR TERSEDIA: air yg terdapat antara kap. Lapang dan koef. Layu. Air perlu ditambahkan untuk mencapai pertumbuhan tanaman yang optimum apabila 50 - 85% air yg tersedia telah habis terpakai.Kalau air tanah mendekati koefisien layu, penyerapan air oleh akar tanaman tdk begitu cepat dan tidak mampu mengimbangi pertumbuhan tanaman

3. AIR TIDAK TERSEDIA: AIR yg diikat oleh tanah pd TITIK LAYU permanen, yaitu air higroskopis dan sebagian kecil air kapiler.

KH KL KP 100 % pori 31 atm 15 atm 1/3 atm Air Air Ruang udara dan Higroskopis Kapiler air drainase

Tdk tersedia Tersedia Berlebihan Daerah Optimum

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Faktor yg mempengaruhi Air Tersedia

Faktor yg berpengaruh:1. Hubungan tegangan dengan kelengasan2. Kedalaman tanah3. Pelapisan Tanah

TEGANGAN MATRIK : tekstur, struktur dan kandungan bahan organik mempengaruhi jumlah air yg dapat disediakan tanah bagi tanaman

TEGANGAN OSMOTIK: adanya garam dalam tanah meningkatkan tegangan osmotik dan menurunkan jumlah air tersedia, yaitu menaikkan koefisien layu.

Persen air Sentimeter air setiap 30 cm tanah

1018 Kap. Lapang

Air tersedia

Koef. Layu 5 6 Air tidak tersedia

Pasir Sandy loam Loam Silty-loam Clay-loam Liat

Tekstur semakin halus

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SUPLAI AIR ke TANAMAN

Dua proses yg memungkinkan akar tanaman mampu menyerap air dlm jumlah banyak, yaitu:

1. Gerakan kapiler air tanah mendekati permukaan akar penyerap2. Pertumbuhan akar ke arah zone tanah yang mengandung air

LAJU GERAKAN KAPILER

LAJU PERPANJANGAN AKAR Selama masa pertumbuhan tanaman, akar tanaman tumbuh memanjang dengan cepat, sehingga luas permukaan akar juga tumbuh terus.Jumlah luas permukaan akar penyerap yang bersentuhan langsung dengan sebagian kecil air tanah (yaitu sekitar 1-2%)

Bulu akar menyerap

air

Jumlah air tanah

berkurang

Tegangan air tanah

meningkat Terjadi perbedaan Tegangan

dg air tanah di sekitarnya

Terjadi gerakan kapiler

air menuju bulu akar

Laju gerakan tgt perbedaan

tegangan dan daya hantar pori tanah

Gerakan kapiler 2.5 cm

sagt penting

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KEHILANGAN UAP AIR

DARI TANAH

HADANGAN HUJAN OLEH TUMBUHANTajuk tumbuhan mampu menangkap sejumlah air hujan, sebagian air ini diuapkan kembali ke atmosfer.Vegetasi hutan di daerah iklim basah mampu menguapkan kembali air hujan yg ditangkapnya hingga 25%, dan hanya 5% yg mencapai tanah melalui cabang dan batangnya.

Awan hujanAwan hujan Pembentukan Awan Pembentukan Awan

Tanah permukaan

Groundwater Batuan

Sungai - laut

presipitasi

infiltrasi

perkolasi

Run off

transpirasi

evaporasi

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Hadangan hujan oleh tanaman

semusim

Sekitar 5 - 25% dari curah hujan dihadang tanaman dan dikembalikan ke atmosfer.Besarnya tergantung pada kesuburan tanaman dan stadia pertumbuhan tanaman .Dari curah hujan 375 mm, hanya sekitar 300-350 mm yang mencapai tanah.

Hadangan curah hujan oleh jagung dan kedelai

Keadaan hujan Persen dari curah hujan total untuk: Jagung Kedelai

Langsung ke tanah 70.3 65.0Melalui batang 22.8 20.4

Jumlah di tanah 93.1 85.4Yang tinggal di atmosfer 6.9 14.6

Sumber: J.L.Haynes, 1940.

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HUBUNGAN ENERGI LTTA:Perubahan tegangan air pd saat bergerak dari tanah melalui akar, batang, daun , ke atmosfer

Potensial negatif air (Tegangan air)

500 300 100 25 20 15 10 5 0

Tanah berkadar air rendah Tanah berkadar air tinggi Tanah

Akar

Batang

Daun

Atmosfer

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EVAPO-TRANSPIRASI

Kehilangan uap air dari tanah:1. EVAPORASI: penguapan air dari permukaan tanah2. TRANSPIRASI: Penguapan air dari permukaan tanaman3. EVAPOTRANSPIRASI = Evaporasi + TranspirasiLaju penguapan air tgt pd perbedaan potensial air = selisih tekanan uap air = perbedaan antara tekanan uap air pd permukaan daun (atau permukaan tanah) dengan atmosfer

Faktor Iklim dan Tanah:1. Energi Penyinaran2. Tekanan uap air di atmosfer3. Suhu4. Angin5. Persediaan air tanah

Air tanah Evapotranspirasi (cm:Jagung Medicago sativa

Tinggi 17.7 24.4Sedang 12.7 20.5

Sumber: Kelly, 1957.

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Ketersediaan Air Tanah vs

Evapotranspirasi

Ketersediaan air di daerah perakaran sangat menentukan besarnya evapotranspirasi.Kedalaman daerah perakaran tanaman 50 - 60 cm.Air tanah pada lapisan olah mengalami pengurangan karena evaporasi permukaan Air tanah pd lapisan bawah mengalami pengurangan karena diserap akar tanaman

Kedalaman tanah (cm) Evapotranspirasi (cm):Jagung Padang Rumput Hutan

0 - 17.5 24.25 23.45 23.2717.5 - 180.0 20.75 21.17 22.25

Sumber: Dreibelbis dan Amerman, 1965.

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PEMAKAIAN KONSUMTIF

(PK)

Pemakaian Konsumtif merupakan jumlah kehilangan air melalui evaporasi dan transpirasi.Lazim digunakan sebagai ukuran dari seluruh air yg hilang dari tanaman melalui evapotranspirasiIni merupakan angka-praktis untuk keperluan pengairan

Dua faktor penting yg menentukan PK adalah:1. KEDALAMAN PERAKARAN TANAMAN2. FASE PERTUMBUHAN TANAMAN

PK dapat berkisar 30 - 215 cm atau lebih:1. Daerah basah - semi arid dg irigasi: 37.5 - 75 cm.2. Daerah panas dan kering dg irigasi: 50 - 125 cm.

EVAPORASI vs TRANSPIRASIFaktor yg berpengaruh adalah:

1. Perbandingan luas tutupan tanaman thd luas tanah2. Efisiensi pemakaian air berbagai tanaman3. Perbandingan waktu tanaman berada di lapangan4. Keadaan iklim

Di daerah basah : EVAPORASI TRANSPIRASIDi daerah kering:

1. EVAPORASI 70 - 75 % dari seluruh hujan yg jatuh2. TRANSPIRASI 20 - 25%3. RUN OFF 5%

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WUE : Water Use Efficiency

WUE Produksi tanaman yg dapat dicapai dari pemakaian sejumlah air tersedia

WUE dapat dinyatakan sbg:1. Pemakaian konsumtif (dalam kg) setiap kg jaringan tanaman yg

dihasilkan2. Transpirasi (dalam kg) setiap kg jaringan tanaman yg dihasilkan

……… NISBAH TRANSPIRASI

Jumlah air yg diperlukan untuk menghasilkan 1 kgbahan kering tanaman

NISBAH TRANSPIRASIUntuk tanaman di daerah humid: 200 - 500, di daerah arid duakalinya

Tanaman Nisbah Transpirasi

Beans 209 - 282 - 736Jagung 233 - 271 - 368Peas 259 - 416 - 788Kentang 385 - 636

Sumber: Lyon, Buckman dan Brady, 1952.

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FAKTOR WUE

Faktor yang mempengaruhi WUE: Iklim, Tanah, dan HaraWUE tertinggi lazimnya terjadi pd tanaman yg berproduksi optimum; Adanya faktor pembatas pertumbuhan akan menurunkan WUE

Nisbah evapo-transpirasi tanaman di lokasi yg mempunyai defisit kejenuhan dari atmosfer800

Kentang Kacang polong400

Jagung 0 0 Defisit kejenuhan dari atmosfer (mm Hg) 12 14

Jumlah air unt menghasilkan 1 ton bahan kering 30

Kadar air tanah rendah

15 Kadar air tanah tinggi0 0 Pupuk P, kg/ha 600

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Pengendalian Penguapan

MULSA & PENGELOLAAN Mulsa adalah bahan yg dipakai pd permukaan tanah untuk mengurangi penguapan air atau untuk menekan pertumbuhan gulma.Lazimnya mulsa spt itu digunakan untuk tanaman yang tidak memerlukan pengolahan tanah tambahan

MULSA KERTAS & PLASTIKBahan mulsa dihamparkan di permukaan tanah, diikat spy tdk terbang, dan tanaman tumbuh melalui lubang-lubang yg telah disiapkanSelama tanah tertutup mulsa, air tanah dapat diawetkan dan pertumbuhan gulma dikendalikan

MULSA SISA TANAMAN Bahan mulsa berasal dari sisa tanaman yg ditanam sebelumnya, misalnya jerami padi, jagung, dan lainnyaBahan mulsa dipotong-potong dan disebarkan di permukaan tanahCara WALIK DAMI sebelum penanaman kedelai gadu setelah padi sawah

MULSA TANAH Pengolahan tanah Efektivitas mulsa tanah dalam konservasi air-tanah (mengendalikan evaporasi) masih diperdebatkan, hasil-hasil penelitian masih snagat beragam

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Olah Tanah vs Penguapan Air

Tanah

Alasan pengolahan tanah: 1. Mempertahankan kondisi fisika tanah yg memuaskan2. Membunuh gulma3. Mengawetkan air tanah.

Pengendalian Penguapan vs Pemberantasan Gulma

Perlakuan Hasil jagung (t/ha) Kadar air tanah (%) hingga kedalaman 1 m

Tanah dibajak dg persiapan yg baik 1. Dibebaskan dari gulma 2.9 22.3 2. Gulma dibiarkan tumbuh 0.4 21.8 3. Tiga kali pengolahan dangkal 2.5 21.9Persiapan Buruk 4. Dibebaskan dari gulma 2.0 23.1

Sumber: Mosier dan Gutafson, 1915.

Pengolahan tanah yg dapat mengendalikan gulma dan memperbaiki kondisi fisik tanah akan berdampak positif thd produksi tanamanPengolahan tanah yg berlebihan dapat merusak akar tanaman dan merangsang evaporasi, shg merugikan tanaman

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Beberapa proses penting dalam siklus air:

Precipitation is condensed water vapor that falls to the Earth's surface.

Most precipitation occurs as rain, but also includes snow, hail, fog drip, graupel, and sleet.

Approximately 505,000 km³ of water fall as precipitation each year, 398,000 km³ of it over the oceans.

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Canopy interception

is the precipitation that is intercepted by plant

foliage and eventually evaporates back to the

atmosphere rather than falling to the ground.

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LIMPASAN = Runoff includes the variety of ways by which water moves across the land. This includes both surface

runoff and channel runoff.

As it flows, the water may infiltrate into the ground, evaporate into the air, become stored in lakes or reservoirs, or be extracted

for agricultural or other human uses.

Infiltration is the flow of water from the ground surface into the ground.

Once infiltrated, the water becomes soil moisture or groundwater.

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Subsurface Flow is the flow of water underground, in the vadose zone and aquifers. Subsurface water may return

to the surface (eg. as a spring or by being pumped) or eventually seep into the oceans.

Water returns to the land surface at lower elevation than where it infiltrated, under the force of gravity or gravity

induced pressures.

Groundwater tends to move slowly, and is replenished slowly, so it can remain in aquifers for thousands of years.

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Evaporation is the transformation of water from liquid to gas phases as it moves from the ground or bodies of water into the

overlying atmosphere. The source of energy for evaporation is primarily solar radiation. Evaporation often implicitly includes transpiration from plants,

though together they are specifically referred to as evapotranspiration.

Approximately 90% of atmospheric water comes from evaporation, while the remaining 10% is from transpiration. Total annual

evapotranspiration amounts to approximately 505,000 km³ of water, 434,000 km³ of which evaporates from the oceans.

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SUBLIMASI is the state change directly from solid water (snow or ice) to water vapor.

ADVEKSI is the movement of water — in solid, liquid, or vapour states — through the atmosphere. Without

advection, water that evaporated over the oceans could not precipitate over land.

KONDENSASI is the transformation of water vapour to liquid water droplets in the air, producing clouds and

fog.

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Aktivitas manusia yang dapat mempengaruhi siklus air :

Pertanian Alteration of the chemical composition of the atmosphere

Construction of dams Deforestation and afforestation

Removal of groundwater from wells Water abstraction from rivers

Urbanization .

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KAPASITAS PENYIMPANAN AIR:WATER HOLDING CAPACITY

Soil "holds" water available for crop use, retaining it against the pull of gravity.

This is one of the most important physical facts for agriculture.

If the soil did not hold water, if water was free to flow downward with the pull of gravity as in a river or canal, we would have to

constantly irrigate, or hope that it rained every two or three days. There would be no reason to pre-irrigate. And there would be no

such thing as dryland farming.

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Soil Moisture Level (Depletion, %) vs. Soil Moisture Tension (Bars).

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Hubungan antara Potensial Air Tanah dnegan Air Tersedia pada

tiga macam tekstur tanah

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The soil's ability to hold water depends on both the soil texture and structure.

Texture describes the relative percentages of sand, silt, and clay particles.

The finer the soil texture (higher percentage of silt and clay), the more water soil can hold.

Gravity is always working to pull water downwards below the plant's root zone.

To counteract the pull of gravity, soil is able to generate its own forces, commonly called "matric forces" ("matric" because of the soil "matrix" structure that forms the basis for the forces).

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An important fact about the soil's water-holding forces is that as the level of soil moisture goes down, the soil generates more force. This is the reason that some water will move up into the root zone from a shallow ground water table. As the plant extracts water in

the root zone, the soil pulls water up from the area with more water to the area with less.

As you would expect, the rate at which the water-holding forces go up with decreasing soil moisture is different for different soils. In a

coarse soil, they will go up slowly. This means that plants can extract a great amount of water from

coarse soils before they stress. In contrast, these forces rise quickly in finer soils.

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Graphically, the relationship can be described by the Figure SWP-1. Looking at the lowest line for a coarse soil.

You can see that at A, the soil moisture level is very high and the water-holding forces are low.

This means that the plant can extract water easily from the soil.

At B, the soil moisture level is lower but the water-holding forces haven't gone up that much.

The plant can still extract water easily.

However at C, the soil moisture level is very low and the water-holding forces have increased greatly.

The plant cannot extract water easily and will be stressed.

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79

Looking at the top line for a finer soil.

At A, as with the coarse soil, the water-holding forces are low when the soil moisture level is high.

However, at B, the soil moisture level has dropped somewhat but the water-holding forces have gone up greatly.

And at C, where the soil moisture level is low, the water-holding forces have gone up very high.

We will be coming back to this idea of increasing soil water-holding forces with decreasing soil moisture many times

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HUBUNGAN TANAH-AIR

The role of soil in the soil-plant-atmosphere continuum is unique. It has been demonstrated that soil is not essential for plant growth

and indeed plants can be grown hydroponically (in a liquid culture).

However, usually plants are grown in the soil and soil properties directly affect the availability of water and nutrients to plants.

Soil water affects plant growth directly through its controlling effect on plant water status and indirectly through its effect on aeration, temperature, and nutrient transport, uptake and transformation.

The understanding of these properties is helpful in good irrigation design and management.

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The soil system is composed of three major components: solid particles (minerals and organic

matter), water with various dissolved chemicals, and air.

The percentage of these components varies greatly with

soil texture and structure.

An active root system requires a delicate balance between the

three soil components; but the balance between the liquid and gas phases is most critical, since

it regulates root activity and plant growth process.

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The amount of soil water is usually measured in terms of water content as percentage by volume or mass, or as soil

water potential.

Water content does not necessarily describe the

availability of the water to the plants, nor indicates, how

the water moves within the soil profile.

The only information provided by water content is the relative amount of water

in the soil.

Jumlah air tersedia dipengaruhi tekstur tanah

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Soil water potential, which is defined as the energy required to remove water from the soil,

does not directly give the amount of water present in the

root zone either.

Therefore, soil water content and soil water potential should

both be considered when dealing with plant growth and

irrigation.

The soil water content and soil water potential are related to each other, and the soil water

characteristic curve provides a graphical representation of this

relationship.

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The nature of the soil characteristic curve depends on the physical properties of the soil namely, texture and structure. Soil texture

refers to the distribution of the soil particle sizes.

The mineral particles of soil have a wide range of sizes classified as sand, silt, and clay.

The proportion of each of these particles in the soil determines its texture.

All mineral soils are classified depending on their texture. Every soil can be placed in a particular soil group using a soil textural triangle .

For example a soil with 60% sand and 10% clay separates is classified as a Sandy loam

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Kapasitas LapanganField Capacity

There are limits on the amount of water that soil holds for crop use. The upper limit is termed "field capacity".

During an irrigation, or whenever excess water is added to soil, water drains down through the soil due to the pull of gravity.

At first, this internal drainage is relatively rapid.

However, it soon slows to almost nothing. (The increasing soil water-holding forces finally start to counteract

gravity.) At this point we would say the soil is at field capacity.

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You can demonstrate field capacity using a visualization of a sponge (like soil, a porous material that will hold water).

Using a pan of water, hold a sponge under water until it is saturated. Now, pull the sponge out of the water.

It will immediately start to drip water, quickly at first, then slower and slower.

At some point it will essentially stop dripping. The internal drainage has stopped and the sponge is at field capacity.

It is very important to note that you can soak more water into soil that is already at field capacity.

There will be open soil pores that will take the water. However, the excess water will not be held.

It will just drain down until the soil moisture returns to field capacity.

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You can use the sponge again to demonstrate this important fact. With the sponge at "field capacity", use a cup to pour water on it.

The water will soak in, there will be open pores in the sponge that will take in water. But you will see that the sponge starts dripping

again as the excess water starts to drain off the bottom.

Because of this ability to hold water against the pull of gravity, soil does not act like a bathtub during irrigations.

That is, irrigation water does not have to go to some "bottom" and then fill back up to the top. Rather soil fills to field capacity from the

top down.

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Field capacity is a soil-based concept.

That is, it depends on the texture and structure of the soil as well as the physical

conditions in the field.

Coarse soils have lower field capacities than fine soils.

If there is a high water table or severe stratification that would restrict drainage, the

field capacity would be higher than normal.

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AIR TERSEDIA & ZONE AKAR EFEKTIF

The water held by the soil between field capacity and permanent wilting point is termed the "available water holding capacity" of the

soil.

It is water that is "available" for the plant to use. Water added to the soil in excess of field capacity will drain down, below the active

root system.

Water held by the soil that is below the permanent wilting point is of no use, the plant has died.

As a crop manager you are concerned with the soil moisture throughout the depth of the plant's active root system, the "effective

root zone".

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The effective root zone is that depth of soil where you want to control soil moisture (just as you control fertility and weed/pest pressures).

The effective root zone may or may not be the actual depth of all active roots. It may be shallower because of concerns for crop quality

or development (as with many vegetable crops). For a pre-irrigation though, you may want to consider the maximum

potential root zone as the effective root zone for that irrigation.

For example, with cotton you may estimate the effective root zone as 6 feet for a preirrigation, 2 feet for the first seasonal irrigation, 4 feet

for the second seasonal, and 6 feet thereafter. For an almond orchard, you may estimate the effective root zone as four feet for the entire season. With onions, the major concern is with the top 2 feet.

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Hubungan Air – Tanah

The soil is composed of three major parts: air, water, and solids . The solid component forms the framework of the soil and consists

of mineral and organic matter. The mineral fraction is made up of sand, silt, and clay particles.

The proportion of the soil occupied by water and air is referred to as the pore volume.

The pore volume is generally constant for a given soil layer but may be altered by tillage and compaction. The ratio of air to water

stored in the pores changes as water is added to or lost from the soil. Water is added by rainfall or irrigation, as shown in Figure 2. Water is lost through surface runoff, evaporation (direct loss from the soil to the atmosphere), transpiration (losses from plant tissue),

and either percolation (seepage into lower layers) or drainage.

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The pore volume is actually a reservoir for holding water. Not all of the water in the reservoir is available for plant use.

Figure 3 represents a "wet" (saturated) soil immediately after a large rainfall.

Note that all of the pores are filled with water. Gravity will pull some of this water down through the soil below the crop's root zone.

The water that is redistributed below the root zone due to the force of gravity is gravitational water. In general, gravitational water is not

available to plants, especially in sandy soils, because the redistribution process occurs quickly (in two days or less).

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Kapan tanah perlu ditambah air agar tanaman tidak terganggu pertumbuhannya?

Jelaskan pendapat Saudara dnegan 250 kata?

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Sumber dan perilaku air yang ditambahkan ke tanah

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Saturated (wet) soil. All pores (light areas) are filled with water. The dark areas represent soil solids.

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Water distribution in a soil at field capacity. Capillary water (lightly shaded areas ) in soil pores is available to plants. Field capacity represents the upper

limit of plant-available water.

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Water distribution in a soil at thw wilting point. This water is held tightly in thin films around soil particles and is unavailable to plants. The wilting point

represents the lower limit of plant-available water.

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Plant-available water, PAW, adalah volume air yang disimpan dalam tanah yang dapat

digunakan oleh tanaman .

It is the difference between the volume of water stored when the soil is at field capacity and the

volume still remaining when the soil reaches the permanent wilting point (the lower limit), as

shown in Figure 6.

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Figure 6. HUBUNGAN ANTARA AIR-TERSEDIA DAN DISTRIBUSI AIR DALAM TANAH .

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Kapasitas tanah menyimpan air

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101Jumlah air tanah pada tiga macam tekstur tanah

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Tabel 1. Jumlah air tersedia dalam tanah yang teksturnya berbeda-beda

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AIR-TANAH dan CEKAMAN (stres) TANAMAN

Kalau tanaman menyerap air dari tanah , jumlah air tersedia yang tersisa dalam tanah menjadi berkurang.

The amount of PAW removed since the last irrigation or rainfall is the depletion volume.

Irrigation scheduling decisions are often based on the assumption that crop yield or quality will not be reduced as long as the amount of water

used by the crop does not exceed the allowable depletion volume. The allowable depletion of PAW depends on the soil and the crop. For example, consider corn growing in a sandy loam soil three days after a

soaking rain. Even though enough PAW may be avai1able for good plant growth, the

plant may wilt during the day when potential evapotranspiration (PET) is high.

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AIR-TANAH dan CEKAMAN (stres) TANAMAN

Evapotranspiration merupakan proses hilangnya air tanah ke atmosfer, melalui evaporasi dari permukaan tanah dan proses transpirasi dari

tanaman yang tumbuh di tanah .

Potential evapotranspiration is the maximum amount of water that could be lost through this process under a given set of atmospheric conditions,

assuming that the crop covers the entire soil sur- face and that the amount of water present in the soil does not limit the process.

Potential evapotranspiration is controlled by atmospheric conditions and is higher during the day. Plants must extract water from the soil that is

next to the roots. As the zone around the root begins to dry, water must move through the

soil toward the root (Figure 7). Daytime wilting occurs because PET is high and the plant takes up water faster than the water can be replaced.

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Gambar.

Kalau tanaman menyerap air, tanah di

sekitar perakaran menjadi mengering .

If the rate of water movement from moist zones is less than the

PET, the plant temporarily wilts.

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Pada malam hari, pada saat PET menurun hingga mendekati nol , air tanah bergerak dari tanah yang lebih basah memasuki zone tanah yang lebih kering di sekitar

akar tanaman.

The plant recovers turgor and wilting ceases (Figure 8).

This process of wilting during the day and recovering at night is referred to as temporary wilting.

Proper irrigation scheduling reduces the length of time a crop is temporarily wilted.

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Gambar .

At night when the PET is low, the plant

recovers from wilting as water

moves from moist zones (dark areas) to eliminate the dry zones around the

roots.

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Hubungan antara distribusi air dalam tanah dan konsep jadwal irigasi ketika 50 percent air tersedia telah habis

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FAKTOR TANAMAN

Three plant factors must be considered in developing a sound irrigation schedule: the crop's effective root depth, its moisture use rate, and its sensitivity to drought stress (that

is, the amount that crop yield or quality is reduced by drought stress).

KEDALAMAN EFEKTIF AKAR

Rooting depth is the depth of the soil reservoir that the plant can reach to get PAW. Crop roots do not extract water

uniformly from the entire root zone. Thus,the effective root depth is that portion of the root zone where the crop extracts the majority of its water. Effective root depth is determined by

both crop and soil properties.

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PENGARUH TANAMAN thd KEDALAMAN EFEKTIF AKAR

Different species of plants have different potential rooting depths.

The potential rooting depth is the maximum rooting depth of a crop when grown in a moist soil with no barriers or restrictions that inhibit root elongation.

Potential rooting depths of most agricultural crops important in North Carolina range from about 2 to 5 feet. For example, the potential rooting depth of corn is

about 4 feet.Water uptake by a specific crop is closely related to its root distribution in the soil.

About 70 percent of a plant's roots are found in the upper half of the crop's maximum rooting depth. Deeper roots can extract moisture to keep the plant alive, but they do not extract suffficient water to maintain optimum growth.

When adequate moisture is present, water uptake by the crop is about the same as its root distribution. Thus, about 70 percent of the water used by the crop comes

from the upper half of the root zone (Figure 10). This zone is the effective root depth.

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JUMLAH AIR YANG DAPAT DISERAP TANAMAN DIPENGARUHI OLEH DISTRIBUSI AKAR DLAMA TANAH

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PENGARUH TANAH thd KEDALAMAN EFEKTIF AKAR.

The maximum rooting depth of crops in North Carolina is usually less than their potential rooting depth and is restricted by soil chemical or physical

barriers.

North Carolina subsoils have a pH of about 4.5 to 5.0, which presents a chemical barrier to root growth, as shown in Figure 11.

Liming practices rarely improve soil pH below the 2-foot depth. Shallow soils (Carolina slate belt soils) or soils with compacted tillage pans (coastal

plain soils) are examples of soils with physical barriers that restrict root penetration below the plow depth (usually less than 12 inches unless

subsoiling is practiced).

Thus, for example, while corn has a potential rooting depth of 4 feet, when grown under North Carolina conditions, its maximum rooting depth is about

2 feet. Maximum rooting depths for several crops under North Carolina conditions are given in Table 2.

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CIRI-CIRI TANAH YANG MEMPENGARUHI KEDALAMAN PERAKARAN TANAMAN

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The effective root depth is the depth that should be used to compute the volume of PAW in the soil reservoir.

The effective root depth for a mature root zone is estimated to be one-half the maximum rooting depth listed in Table 2.

For example, under North Carolina conditions corn has a maximum rooting depth of 2 feet; thus, the maximum effective root depth is

estimated to be 1 foot.

Effective root depth is further influenced by the stage of crop development. Effective root depths for most aops inaease as top

growth inaeases until the reproductive stage is reached. After this time, effective root depth remains fairly constant.

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Kedalaman perakaran tanaman jagung pada berbagai umur pertumbuhannya. Jadwal irigasi harus didasarkan pada kedalaman efektif

akar dan bukan pada kedamalan maksimum perakaran .

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LAJU PENGGUNAAN AIR TANAMAN

Often, irrigation scheduling requires an estimate of the rate at which PAW is being extracted. A "checkbook" approach is often used to keep a daily

accounting of water additions and removal. Traveling irrigation systems usually require several days to complete one

irrigation cycle. Soil-water measurements should be used to schedule irrigation for these systems, but continued PAW extraction during the irrigation cycle must also be estimated so that the last part of the field

does not get too dry.

In the above situations, the crop's water use rate must be estimated. Estimates of the water use rate for most crops are available from county Extension Service or Soil Conservation Service offices. As with rooting

depth, water use rate is a function of the crop's stage of development, as shown in Figure 13.

For example, corn uses water three times as fast during the pollination period (65 to 75 days after planting, 0.25 inch per day) as during the knee-

high stage (35 to 40 days after planting, 0.08 inch per day).

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Penggunaan air harian tanaman jagung dipengaruhi oleh fase pertumbuhan tanaman . Jadwal irigasi harus disesuaikan dengan

perubahan konsumsi air tanaman selama musim pertumbuhannya

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KEPEKAAN TANAMAN TERHADAP KEKERINGAN

The reduction in crop yield or quality resulting from drought stress depends on the stage of crop development. For example, corn is most susceptible to stresses caused by dry conditions at the siLicing stage

(Figure 14).

For a given level of stress, the yield reduction for corn would be four times greater at the silking stage than at the knee-high stage. From the yield

standpoint, applying irrigation water at silking would be worth four times more than if the same amount of water was applied during the knee-high

stage. Knowledge of this relationship is most useful when the irrigation capacity or water supply is limited. When water is in short supply, irrigation should be delayed or cancelled during the least susceptible crop growth stages.

This water can then be reserved for use during more sensitive growth stages.

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119

Kepekaan tanaman jagung terhadap kekeringan dipengaruhi oleh fase pertumbuhannya. Semakin besar tingkat kepekaannya, maka

pengaruh kekeringan terhadap hasil semakin besar.

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Kepakaan tanaman jagung terhadap kekeringan dipengaruhi oleh umur tanaman.

This relationship is typical for most agricultural crops irfigated. The most critical irrigation period typically begins just before the reproductive stage and lasts about 30 to 40 days to the end of the fruit enlargement or grain development stage. Because the root

system is fully developed by the beginning of the reproductive period, irrigation amounts should be computed to replace the depleted PAW

within the effective root zone (12 inches). Exceptions include tobacco and other transplanted crops where irrigation is often scheduled immediately after transplanting to

ensure stand establishment.

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When if rigation is scheduled before the crop root system is fully developed, the amount of irrigation to apply should be based on the depleted PAW within the actual effective root depth at the time of

irrigation. For example, irrigation scheduled when corn is at the knee-high stage (35 to 40 days after planting) should apply only about two-

thirds as much water as an irrigation scheduled during the tasseling stage (65 days after planting) because the effective rooting depth at the knee-high stage is only two-thirds as deep (8 inches compared to

12 inches).

For soils that have an abrupt textural change within the effective root depth, such as a loamy sand surface texture overlying a sandy

clay loam, a correction may be necessary to account for the different amounts of PAW within each soil texture.

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123

Jumlah air tanah tersedia dalam berbagai tipe tanah

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124

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125

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126

Bagaimana mycorrhiza dapat membantu penyerapan air dari dalam tanah? Uraian 250 kata

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127

Jelaskan mengapa

air bergerak dari akar menuju

daun tanaman ?

250 kata

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128

Jelaskan klasifikasi biologis air tanah, dengan 250 kata

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129

Pengaruh Potensial Air tanah thd konduktivitas hidraulik tanah

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130Pengaruh ketersediaan air terhadap pertumbuhan tanaman

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131

Pola penyerapan air oleh tanaman yang tumbuh pada profil tanah yang tidak mempunyai lapisan penghambat dan suplai air tersedia

cukup di seluruh zone perakaran tanaman

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Sistem Perakaran Serabut dan Perakaran Tunggang pada Tanaman umur dua bulan

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Penyerapan air BAWANG PUTIH (Allium cepa)

Tanaman mempunyai sistem perakaran yang dangkal dan akar-akar terkonsentrasi pada tanah klapisan atas sedalam 0.3

m.

Pada umumnya 100% penyerapan air terjadi dari lapisan tanah atas sedalam 0.3-0.5 m (D=0.3-0.5 m ).

Untuk memenuhi sekuruh kebu tuhan air tanaman (ETm) tanah harus dijaga tetap lembab; pada laju evapotranspirasi 5-6

mm/hari ternyata laju penyerapan air mulai menurun kalau sekitar 25% dari total air tanah tersedia telah habis (p = 0.25).

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Penyerapan air tanaman LOMBOK (Capsicum annum dan Capsicum frutescens)

Tanaman lombok mempunyai akar utama yang patah pada saat trans planting dan kemudian menumbuhkan banyak akar-akar lateral.

Kedalaman akar dapat meluas hingga 1 m tetapi pada kondisi irigasi ternyata akar terkonsentrasi pada lapisan tanah atas seda lam 0.3 m.

Pada kondisi evapoytranspirasi maksimum 5-6 mm/hari, 25-30% total air tersedia dapat dihabiskan sebelum terjadi reduksi penyerapan air (p=0.25-

0.30).Biasanya 100% penyerapan air terjadi dalam keda;laman lapisan tanah

0.5 - 1.0 m (D = 0.5-1.0 m).

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Penyerapan air tanaman jeruk

Tanaman jeruk menumbuhkan satu akar tunggang utama. Akar-akar cabang membentuk semacam jaring horisontal yang dilengkapi dengan bulku-bulu akar. Perkembangan akar snagat tergantung pada tipe

batang bawah yang digunakan dan karakteristik profil tanah. Kedalaman perakaran beragam antara 1.20 dan 2.0 m. Pada umumnya

60% akar berada pada lapisan tanah atas 0.5 m, 30% dalam lapisan tanah 0.5 m ke dua, dan 10% pada lapisan tanah di bawah 1 meter.

Kalau persediaan air irigasi mencukupi, biasanya 100% air diekstraks dari lapisan tanah atas 1.2 - 1.6 m (D = 1.2-1.6 m) tetapi pada kondisi kering

ternyata kedalaman ek straksi air lebih dalam lagi.

Selama periode defisit air yang panjang, air dalam tanah yang kedalaman efektifnya tebal dan drainasenya bagus dapat digunakan oleh tanaman

hingga kedalaman 2 atau 3 meter.

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136

Pergerakan air dari lapisan tanah basah ke lapisan tanah kering dengan bantuan sistem perakaran tanaman

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BAGAIMANA TANAMAN MENGAMBIL AIR?

Apa kebutuhan tanaman?

Plants need water. We all know that. Why do they need water? For the following reasons:

Firstly, they need water in order to stand up. Some will eventually make woody tissue to help this process, but basically plants are full of pressurised water which makes them turgid. The leaves offer themselves to the sun....their stomata (pores)

open....and moisture evaporates. Water is drawn upward from the roots and through the stems to replace this lost water. This process is called

"evapotranspiration". The more sun, the greater the pressure to take up water. This process takes energy from the plant, and obviously requires a healthy root system and the presence of AVAILABLE water in the root zone (I'll explain the

"availability" shortly). If it's not there, the plant will wilt. In cases of root disease and diseases like Fusarium, you will see whole crops crash down.

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Secondly, they need water to carry nutrients into themselves which are dissolved in the soil water. They can't munch on dry fertiliser.

No water.....or I should say, "no passage of water into the plant"...... and no nutrient uptake.

If the plant can't take up water, it will become starved of nutrients. It's not so uncommon to see high nutrient soils and pale, nutrient-starved crops because of an inability of the plant to take up water.

Thirdly, plants need water to photosynthesize. To summarise a fairly complex process, photosynthesis is the

synthesis of sugar (energy) from light, carbon dioxide and water, with oxygen as a by-product.

Take away any of those factors, and the plant won't grow. It has no energy.

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Apa lagi kebutuhan tanaman ?

They need oxygen, and they need it in the root zone. Like all aerobic organisms (including us), they need to respire as part of the process of utilising the sugars they created in photosynthesis,

and this requires oxygen. No oxygen, and no respiration. No respiration, and no functionality.

The roots can't grow....and can't take up water....and can't supply the plant with the nutrients and water that it needs.

This is why we talk about a plant needing DRAINAGE. The problem in a waterlogged situation is not too much water......it's

too little oxygen!

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AIR DALAM TANAH

Soil is made up of soil particles in crumb-form (peds), and pore spaces around the soil crumbs.

In a well-structured soil, these crumbs are nice and stable....but in a poorly structured soil, the crumbs are unstable which often limits

pore-space.

The pore-spaces are necessary for holding water, and for the free gaseous exchange of oxygen and carbon dioxide between the plant

roots and the soil surface (respiration process).

There are three types of soil water (ie. water in the soil).                                                                                                           

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AIR GRAVITASI

This is the water which is susceptible to the forces of gravity. It exists after significant rainfall, and after substantial irrigation. This is the water which fills

all the pore-space, and leaves no room for oxygen and gaseous exchange. In "light" soils, this tends to drain away quickly. In heavy soils, this can take time.

AIR KAPILER

This is the water which is held with the force of SURFACE TENSION by the soil particles, and is resistent to the forces of gravity. This is the water which is

present after the gravitational water has drained away, leaving spaces free for gaseous exchange. When the soil is holding it's MAXIMUM capillary water

(after the gravitational water has drained), this is called FIELD CAPACITY. At this point, the plant is able to take up water easily, and has the oxygen that it

needs in the root zone.

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AIR HIGROSKOPIS

This is the water which is held so tightly (by surface tension) to the soil particles that the plant roots can't

take it up.

It's there.......but it's unavailable.

At this stage there's generally sufficient oxygen, but there just isn't enough available water.

The plant wilts, and will eventually die if it doesn't get water.

When the plant wilts and is unable to recover, this is called the TITIK LAYU PERMANEN

Titik layu permanen

merupakan sifat tanah yang

penting bagi pertumbuhan

tanaman.

Mengapa demikian?

Jelaskan

dengan 250 kata

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143

TITIK LAYU PERMANEN

The closer to the soil particle the water is held, the tighter it's held. And the further from the particle, the looser it's held. It takes little energy for the plant roots to take up the water that's far from the particle and is present at the field

capacity point. By contrast, as the water is used up (or evaporates), it takes more and more energy for the plant to take up water.

                                                                                                                        I often use the analogy of drinking through a straw. A short straw, ie. when a

cup is 15 cm away from you, is easy to use. A one-metre long straw takes a lot of energy to suck up a drink. A twenty-metre straw is impossible to use. It works much the same with plants. The more the soil dries out, the more energy the

plant needs to output in order to get a decent drink. The effect of increased soil salinity (due to high soil salinity, high soil-water

salinity, or both) has basically the same effect as a soil drying out. Salt in the soil has as osmotic effect, and causes the water to be held more tightly around the soil particles. The higher the salinity level, the harder it is for a plant to take a

drink, despite apparently sufficient moisture present.

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144

Jelaskan pendapat Saudara

mengenai pentingnya sirkulasi air

dalam sistem Tanah-Tanaman

250 kata

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145

Bibit tanaman tomat yang baru

ditanam ini memerlukan cukup

banyak air dari dalam tanah.

Mengapa demikian?

Jelaskan

dengan 250 kata

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146

Struktur Sistem Tanah-

Tanaman.

Jelaskan bagaimana air

dari tanah memasuki

sistem tanah-tanaman.

250 kata

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147

Bagaimana peranan

tumbuhan dalam siklus air di alam?

Jelaskan pendapat Saudara

250 kata

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Representasi ketersediaan air dalam tanah bagi pertumbuhan tanaman

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AIR TERSEDIA BAGI TANAMAN

In other words, Plant Available Water (PAW) is the amount of water held in a soil between the limits of Field Capacity and

Permanent Wilting Point.

However, only the water near to Field Capacity may be Readily Available Water (RAW).

This is particularly so for fine textured, clayey soils because a high proportion of PAW is held in small pores and as thin

films and plants need to 'do more work' to extract this fraction of water from soils.

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RAW - Readily Available Water(Air Mudah Tersedia)

Not all PAW is equally available to plants.

As soils dry out and PAW approaches PWP, plants will come under water-stress and wilt. It is the objective of irrigators to avoid this

situation.

They prefer to irrigate when the soil water content is about 50% of FC or about 100kPa.

These limits, however, are set by the irrigator to suit the business enterprise. For example, if growth rates are to be restricted then the

trigger for an irrigation event may be 300kPa.

As the name suggests, Readily Available Water or RAW is the amount and availability of water in soils that is readily available to plants.

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PAW - Plant Available Water

Following rainfall, or irrigation, all the pores in soil will be filled with water; this is the Saturation Water Content (SWC). With time the water in the

largest pores will drain to depth due to gravitational forces.

In coarser textured, sandy and loamy soils this drainage will take place in less than a day and will, therefore, be unavailable to plants.

Fine-textured, clayey soils, however, may be somewhat poorly drained and all pores may remain filled with water for several days.

In these cases some of the SWC may be available for EvapoTranspiration and would need to be considered in calculations of soil water balances and

irrigation scheduling. Poorly drained soils, however, are less suitable for irrigation.

They are difficult to manage and may be waterlogged for times that can cause damage to plants for reasons of anaerobic root environments.

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152

Jelaskan bagaimana

hubungan antara Evapotranspirasi

dan Irrigasi

Dengan 250 kata

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153

Evapotranspirasi dan Irrigasi

Evapotranspiration (ET) is the combined process of plant transpiration and soil evaporation .

Plant transpiration is the movement of moisture from the plant to the air through tiny pores in the leaves known as stomates.

The water enters the plants through the roots in a liquid form and leaves the plants through the

stomates in a gaseous form.

Soil evaporation is the direct evaporation of water from the surface of the soil into the atmosphere.

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154

Hubungan antara profil tanah dengan

air tanah.

Jelaskan pendapat Saudara

tentang hal ini

250 kata

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155

Hubungan antara kadar

air tanah dnegan nilai pF, pada tiga

macam tekstur tanah.

Jelaskan pendapat Saudara

tentang hal ini

250 kata

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156

Transport air dalam tanaman

Plants need raw materials like CO2, water and minerals for photosynthesis and for various other purposes such as making of

proteins. For plants soil is the richest source of water and minerals.

Roots absorb these substances and transport to the various parts of the plant.

The water and minerals dissolved in it move through special tissue present in plants called xylem.

Xylem consists of two kinds of elements called tracheids and vessels.

Vessels and tracheids of the roots, stems and leaves are interconnected to form a continuous system of water conducting channels reaching all

parts of the plant.

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157

Page 158: Air Tanah Dan Tanaman

158Struktur jaringan pembuluh tanaman

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159

Struktur jaringan pembuluh tanaman

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PERGERAKAN AIR TANAH

During long-continued heavy rains, infiltration of soil water continues under the force of gravity, carrying the water down to successively greater depths. Soil pores become filled with water, with only a small amount of free air remaining entrapped

in bubbles. The soil may, for a time, become almost completely saturated with water.

Downward percolation continues beyond the soil water belt into the intermediate belt, a zone too deep to be reached by plat roots. Water may ultimately reach the

ground-water zone below .

After the rain has ceased, water continues to drain downward under the influence of gravity, but some remains held in the soil, clinging to the soil grains in thin films,

by the force of capillary tension. This is the same force that causes ink to be drawn upward in a piece of blotting

paper and which permits small water droplets to cling to the side of a vertical pane of glass. Films of capillary water in the soil remain held in place until gradually

dissipated by evaporation or drawn into root systems.

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PERGERAKAN AIR TANAH

After soil has been saturated by prolonged rains and then drains until no more water moves downward under the force of gravity, the soil is said to be holding its field capacity of water. Most excess water drains out in a day’s time; usually

not more that two or three days are required for gravity drainage to cease. Soil-moisture content can be stated in terms of the equivalent depth in inches of water in a given thickness of soil. At field capacity, soil-moisture content ranges

from 1 to 4 inches per foot of soil, depending upon soil texture .

Sandy soils have low field capacity, which is rapidly reached because of the ease with which the water penetrates the large openings (macro pores). Clay soils, on the other hand, have a high field capacity, but require much longer periods to attain it because of the slow rate of water penetration due to the much smaller

openings (micro pores).

A comparable, but lower value of soil moisture is the wilting point, below which foliage wilts because of the inability of the plants to extract the remaining

moisture .

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162

A few points to consider:

Only after heavy rainfall does the water “flow” through the soil. This is especially true in our area where evapotranspiration exceeds precipitation. During most of

the growing season the water can be said to be “pulled” through the soil by capillarity.

Field Capacity can be thought of as “all the water a soil can hold against the pull of gravity”.

When the field capacity of a particular soil is exceeded, water begins to flow downward. One last point to consider is that available water to the plant is only

the water held in the soil at tensions between field capacity and wilt point, or realistically, the water held at tensions less than wilt point.

The characteristic annual cycle of changes in soil moisture content deserves study because it leads to a better understanding of the principles of ground-water

movement, surface runoff, and various aspects of the sculpturing of the land by running water.

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Hubungan Air – Tanah – dan

Tanaman

Suatu sistem yang kontinum.

Jelaskan pendapat Saudara mengenai

hal ini

(sebanyak 250 kata)

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164

Air tanah pada berbagai kondisi kelengasan (kadar air)

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165

Struktur Tanaman

Tanaman menyerap air dari dalam tanah

melalui akar-akarnya, kemudian diangkut ke daun untuk fotosintesis

Jelaskan bagaimana akar tanaman

menyerap air dari dalam tanah?

dengan 250 kata

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166

AKAR TANAMAN

Often roots are overlooked, probably because they are less visible than the rest of the plant. However, it's important to understand

plant root systems because they have a pronounced effect on a plant's size and vigor, method of propagation, adaptation to soil

types, and response to cultural practices and irrigation.

Roots typically originate from the lower portion of a plant or cutting. They have a root cap, but lack nodes and never bear leaves

or flowers directly.

Their principal functions are to absorb nutrients and moisture, anchor the plant in the soil, support the stem, and store food. In some plants,

they can be used for propagation.

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167

Struktur akar tanaman

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168Penampang melintang akar tanaman

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169

Pengolahan tanah sawah memerlukan banyak air Pengolahan tanah

sawah untuk menanam padi memerlukan banyak air.

Mengapa demikian?

Jelaskan

dengan 250 kata

Page 170: Air Tanah Dan Tanaman

170Penanaman bibit padi juga memerlukan banyak air

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171

How Rice Is Grown

The two major types of rice, indica (long-grain) and japonica (medium- and short-grain) do well in different environments. Long-grain indica rices (basmati and jasmine, for example) do

well in hot, equatorial climates. Medium- and short-grain japonica rices grow well in temperate and mountainous

regions. Rice cultivation has traditionally been well-suited to countries

and regions with low labor costs and high rainfall. Without modern technology, rice is very labor-intensive to cultivate;

either way it requires plenty of water for irrigation.

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Kebutuhan air tanaman :

"kedalaman (jumlah) air yang diperlukan untuk memenuhi kehilangan air melalui evapotranspirasi (ETtanaman) tanaman yang sehat, tumbuh pada

sebidang lahan yang luas dengan kondisi tanah yang tidak mempun yai kendala (kendala lengas tanah dan

kesuburan tanah) dan mencapai potensi produksi penuh pada kondisi lingkungan tumbuh tertentu".

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AIR TANAMAN

Water is essential in the plant environment for a number of reasons. Water transports minerals through the soil to the roots where they are absorbed by the plant. Water is also the principal medium for the chemical and biochemical processes that support

plant metabolism. Under pressure within plant cells, water provides physical support for plants.

It also acts as a solvent for dissolved sugars and minerals transported throughout the plant. In addition, evaporation within intercellular spaces provides the cooling mechanism that allows

plants to maintain the favorable temperatures necessary for metabolic processes.

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HUBUNGAN TANAH-AIR

The role of soil in the soil-plant-atmosphere continuum is unique. It has been demonstrated that soil is not essential for plant growth

and indeed plants can be grown hydroponically (in a liquid culture).

However, usually plants are grown in the soil and soil properties directly affect the availability of water and nutrients to plants.

Soil water affects plant growth directly through its controlling effect on plant water status and indirectly through its effect on

aeration, temperature, and nutrient transport, uptake and transformation. The understanding of these properties is helpful in

good irrigation design and management.

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Komponen Neraca Air pada Suatu Lahan

Air Irigasi

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176

Hubungan antara Kadar Air Tanah dan Pertumbuhan Tanaman

Growth of most agricultural crops is

favored by a soil water content that is high enough to encourage crop growth and development, but not

so high that aeration becomes restrictive.

If soil water is plant-extracted to levels

approaching the PWP, water is held so tenaciously by the soil that plants can no longer obtain sufficient water to meet the potential

for transpiration. Transpiration is restricted and yield losses take place.

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IRRIGATIONA. Definition: Supplying water to plants in an artificial manner. (39% of all freshwater in the US is used to irrigate crops)

1. Ancient practice – first irrigation used ditches to divert rivers and streams.

2. California agriculture relies on irrigation.

a. Mediterranean climateb. Crop diversificationc. Economics

Page 178: Air Tanah Dan Tanaman

178

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Soil Water and Groundwater (1)