Soil Nutrient Sources and NutrientUptake

Photosynthesis

Plants use light energy and chlorophyll to make sugars for plant growth from water and carbon dioxide.

6 CO2 + 12 H2O C6H12O6 + 6O2 + 6H2O

Light and Chlorophyll

Carbon dioxide Water Glucose Oxygen Water

Functions of Nutrients in Plants

• Carbon, Hydrogen and Oxygen make up 95% of the dry matter weight of plants.

– Carbon dioxide from air is converted in the plant to sugars, starches, proteins, enzymes, and a multitude of other organic compounds.

– Oxygen is a component of most organic compounds, must be present for plant roots to function.

– Hydrogen and oxygen form water which makes up most of the weight of living plants. Hydrogen is a constituent of most organic compounds and is involved in many of the chemical reactions in the plant.

17 Essential Plant NutrientsSource of Plant Nutrients

From AirCarbon (C)

Oxygen (O)

From WaterHydrogen (H)

Oxygen (O)From Soil

Nitrogen (N) Calcium (Ca) Boron (B)

Phosphorus (P) Magnesium (Mg) Chlorine (Cl)

Potassium (K) Sulfur (S) Copper (Cu)

Iron (Fe)

Manganese (Mn)

Molybdenum (Mo)

Zinc (Zn)

Nickel (Ni)

Partially decomposed residue of plants, animals, etc. Humus is the more stable residue 1-3%

decomposes annually

Soil Organic Matter -

• Improves soil structure, water holding capacity, etc.• Provides for good soil tilth• Provides CEC• Source of essential plant nutrients

90-98% of N abd S30-50% of P;Micronutrients

SOIL ORGANIC MATTER

Soil Microbes Mineralize and Immobilize Plant Nutrients.

Plant UnavailableForm

Plant AvailableForm

Organic nutrients Inorganic nutrientsMineralization

Immobilization

Factors Affecting Organic Matter Levels

TemperaturePrecipitationDrainageVegetationTillage

Erosion

Effect of Temp and Moisture on Soil Organic Matter

Soil Organic Matter Content Changes Since Cultivation

Estimated Residue Production by Various Crops ??

lb per bu yieldWheat 100Corn 60Sorghum 60Soybean 45Sunflower 36

NRCS – calculation factor

Crop Residue Decomposition Assumptions

Weight of Plow Layer (6-7”) of Soil Equals 2,000,000 lb/acreCrop Residues are about 43% Carbon (C) About 67% of residue carbon is lost as microbial CO2 If Adequate N Available. May be 75 - 80% loss if N is limiting.Assume SOM is 59% carbonAbout 1-3 % of SOM is decomposed each year

Increasing SOM Content

Assume 45 bu/a wheat provides 4,500 lbs residue4,500 lb residue x 43% C = 1,935 lbs Total C/A1,935 lbs C x 67% = 1,300 Lbs C Respired By Microbes1,935 - 1, 295 = 640 lbs Carbon Remaining

640 / 59% = 1,085 lbs SOM Formed

Assume A Soil With 2% SOM and 2% Is Mineralized Per Year = 800 lbs SOM Mineralized Per Year

Net SOM addition = 1,085 – 800 = 284 lbs SOM per year

Effect Of 20 Years Residue Management(KSU, Ottawa)

20 Year YieldResidue

TreatmentGrainBu/a

Residue Ton/a Soil pH

Organic Matter

Removed 1178 27.4 6.0 3.0Normal 1190 27.8 6.1 3.3Doubled 1175 27.7 6.2 3.7

Effect Of 20 Years Wheat Residue Management(KSU, Holcomb)

Residue Treatment Soil pH

Bray P (ppm)

Exch. K (ppm)

Org. Matter

Burned 8.0 28 515 1.8Removed 8.0 24 500 1.7Normal 7.9 26 540 1.8Double 7.9 20 570 2.0

LSD (0.05) 0.1 NS 20 0.1

Effect of N Rate and Tillage Method on Soil Organic Matter Content

_________________________________________________________Depth,N Soil Organic Matter

in. Rate No-Till Conventional _________________________________________

Lb/Acre % %

0-2” 0 3.70 2.1675 5.08 2.41

150 4.82 2.40

2-6” 0 1.88 2.3875 2.21 2.40

150 2.34 2.31 _________________________________________

2 in

Fonte: Juca Sá

No-till promotes fungal activity

Cation Exchange Capacity

CEC

Ions are Electrically Charged MoleculesCation: Positively Charged Ion +Anion: Negatively Charged Ion -

NutrientCations in Soil Anions in Soil Potassium NitrateAmmonium SulfateMagnesium PhosphateCalcium ChlorideManganese BorateZinc MolybdateHydrogen

NonnutrientsSodium HydroxylAluminum Bicarbonate

Carbonate

Microscopic View of Clay• Layered much like mica

or a deck of cards• Expand and contract with

moisture• Ions like K+ can be

trapped between the layers.

K+

WITH A MAGNET IN THE SOIL

Unlikes Attract Likes Repel Unlikes Attract Likes Repel

CLAY

CLAY

NO3 - NITRATE

PO 4-

PHOSPHATE

CLAY

CLAY

NH4+

AMMONIUM

Ca++ CALCIUM

Surface Charges of Soil Colloids

The Tremendous surface area of soil colloids has a net negative electrical charge.

Clay

NH4+

Ammonium

Unlikes attract Clay -

NONitrate

3-

Likes Repel

Cations Are Not ‘Stuck’ To CEC Sites –They ‘Exchange’ With Cations In Soil Solution

SO=4

Soil Colloid

Cl-

K+ Mg++Ca++ Ca++

NH+4

NO-3

H2PO-4

Na+ Na+

Soil Solution

CEC Sites

Effect of Soil-herbicide Bonding on Herbicide Performance

ClaySoil Solution or Vapor Phase

Herbicide

Organic Matter

Herbicide

Equilibrium reaction, not a permanent bonding to soil

• Cation exchange capacity is the result of permanent negatively charged sites on soil colloids - clays and soil organic matter

• Cations can attach to these sites and detach again in exchange for other cations

• CEC is expressed in mmol per 100 gm soil of soil

How Soil Retains Nutrients

Soil’s CEC indicates several properties

• CEC 15-40 (High)– High clay and humus– More lime needed to

correct pH– Greater capacity to

hold nutrients– High water-holding

capacity

• CEC 1-10 (Low)– High sand content– Less lime needed to

correct pH– Nitrogen and

potassium leaching more likely

– Low water-holding capacity

Cation Exchange Capacity

Soil Texture Type CEC meq./100g.Sands 2-5

Sandy Loam 5-12

Loams 10-18

Silt and Silty Clay Loams 15-30

Clay and Clay Loams 25-40

Soil Colloid Exchange Capacity(meq/100 grams soil)

Kaolinite 3 -15Illite 20 – 40

Montmorillonite 20 – 100Organic Matter 100 - 300

Cation Exchange Capacity

Cation Exchange Capacity (CEC)What Does Soil CEC Do? How Do We Use?

Indicates the soils ability to supply cations

Affects the amount of limestone needed to correct soil acidity

Provides an estimate of soil texture (% clay)

Mobile and Immobile Nutrients

Roots absorb nutrients from the water film

Immobile nutrients, such as P and K, do not move far

Water Film

Soil Colloid

(clay or humus)

Root Hair

Ca++

NH4+

K+

Mg++

NO3-

SO4=

H+

H+

K+

Zn++H+H+

K+

HPO4=

Ca-H2PO4

H+Ca++

H+NO3-

Cation Bonding StrengthCations with greater bonding strengths are held on exchange sites more tightly and are released into the soil water solution less easily than others.

Cation Bonding Strength1. Hydrogen Strongest

2. Aluminum

3. Calcium

4. Magnesium

5. Potassium

6. Ammonium

7. Sodium Weakest

The Concept of the Most Limiting Factor

“Just as the capacity of the wooden bucket to hold water is determined by the height of the shortest stave, crop yields are restricted by the nutrient in shortest supply!”

Corn Dry Matter Accumulation

Corn Nitrogen Uptake

Corn Phosphorus Uptake

Seed Root System

Plant depends on the energy reserves from

the seed until permanent roots are

developed

Corn Potassium Uptake

Grain Sorghum Nutrient and Dry Matter Accumulation

Relative N Uptake for Wheat

0

20

40

60

80

100

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32Weeks after Emergence

Perc

ent N

Upt

ake

JointingJointing

Tillering CompleteTillering Complete

FF MM AA MMJJDDNN

BootBoot

Mechanisms of Nutrient Uptake

Nutrients are absorbed by roots as ions from the soil water or solution.

• Diffusion - movement of ions from a zone of high concentration to a zone of lower concentration. – Short distances: Immobile nutrients

• Mass Flow - movement of ions in soil solution as water moves.– Longer distances: Mobile nutrients

• Root Interception - root grows to the nutrient – Unexplored soil zone

Relative Importance of Soil Supply Mechanisms*

Supply Mechanism, %Nutrient Interception Mass Flow Diffusion

Nitrogen 1 99 0

Phosphorus 3 6 94

Potassium 2 20 78

Calcium 171 429 0

Magnesium 38 250 0

Sulfur 5 95 0

* 150 bu/A corn crop Barber, 1995

Root Competition for Mobile Nutrients

• Roots compete for mobile nutrients with other plants

• Roots compete little for immobile nutrients with other plants.

• What is effect of plant population or weeds on competition for mobile and immobile nutrients?

Nutrient Mobility & Plant Competition

• Mobile nutrients:– Suited to surface

application.– Large root uptake

zone

• Immobile nutrients:– Incorporated.– Limited root uptake

zone

Root Patterns For Several Crops

Potato SugarBeet Soybean Corn Alfalfa

Depth

in

Feet

0

2

4

6

Small Grains

Crop Rooting Patterns

• Crops having deep roots can absorb water and mobile nutrients from the subsoil.

• Fertilization generally increases plant root growth.

• Nutrient mobility and crop rooting patterns affect fertilizer placement.

• Soil Sampling Recommendations:– Sample the surface 0 – 6” depth for immobile nutrients,

such as P and K.– Sample 0 – 24” deep for N, Cl and S since they are soluble,

mobile nutrients.

Soybean Roots (left)Corn Roots (right)

5’

Corn Root System Development

36 Days

8 Weeks

MatureSource: Weaver, 1926

Soil Nutrient Sources and NutrientUptake

Review Exercise1. Three essential elements involved in photosynthesis are carbon, oxygen, and hydrogen.

a. True. b. False.

2. Indicate which groups are primary nutrients __________, secondary nutrients __________, and which are micronutrients ____________________:

a. Boron, copper, iron.

b. Nitrogen, phosphorus, potassium.

c. Aluminum, sodium, fluorine.

d. Calcium, magnesium, sulfur.

3. Soil colloids (clay and organic matter) have __________ electrical charges on their surfaces. a. Positive. b. Negative. c. Neutral. d. No.

4 P i i l h d i ll d i hil h i h i h i

5. Which one of the following generally is the largest contributor to CEC in most soils?

a. Sand. b. Silt. c. Clay. d.Humus.

6. __________ is an important plant nutrient in cation form.

a. Potassium. b. Sodium. c. Nitrate. d. Phosphate.

7. CEC, an abbreviation for Cation Exchange Capacity, is an important measure of the amount of cations a soil can hold in an exchangeable form.

a. True. b. False.

88.oils with a relatively high cation exchange capacity of 15 to 40 meq/100 g can generally be expected to have 89.: High capacity to hold nutrients b High sand content

9. __________ and __________ are considered immobile nutrients in most soils while __________ and __________ are mobile nutrients, easily transported by soil water.

a. Na + b. H2 PO4- c. K + d. NO3

- e. SO4

10. Soil sampling of the surface 6-7” soil layer only is recommended for __________ nutrients while deeper sampling is recommended for __________ nutrients.

a. Mobile. b. All. c. Immobile. d. Organic.

111.he judicious use of fertilizer generally increases plant root growth and the ability of roots to forage for water and nutrients. a. True. b. False.

12. Immobile nutrients are taken up by plant roots primarily through:a. Diffusion of nutrient ions to the root

b. Mass flow of water to the root