Agricultural Water Management, 23 (1993) 303-313 303 © 1993 Elsevier Science Publishers B.V. All fights reserved. 0378-3774/93/$06.00

Use of an hydrophilic polymer to improve water storage and availability to crops grown

in sand dunes I. Corn irrigated by trickling

M. Silberbush a, E. A d a r b and Y. De Malach c aBen-Gurion University of the Negev, Jacob Blaustein Institute for Desert Research, Desert

Agrobiology Center, Sede Boker Campus, Israel ~Ben-Gurion University of the Negev, Department of Geology and Water Resources Research Center,

Jacob Blaustein Institute for Desert Research, Sede Boker Campus, Israel CRamat Negev Agricultural Experiment Station, M.P. Haluza, Israel

(Accepted 29 December 1992)

ABSTRACT

The polyacrylamid (PAM) hydrophilic gel Agrosoak ® was tested as a soil conditioner for improv- ing water availability to crops grown on sand dunes. Corn (Zea mays L.) was grown in the field, in a factorial design array using four rates of Agrosoak (0.00, 0.15, 0.30, 0.45% by weight in the upper 25 crn of the soil), three water amounts (70, 85 and 100% of the recommended Class A evaporation pan ratio ), and two water salinity levels ( 1.2 and 6.5 dS. m- ~ ). Irrigation and fertilization were provided by trickling. The water storage capacity of the soil increased with the rate of Agrosoak but the applied water was accumulated and stored in the vicinity of the emitters leaving relatively dry sections be- tween the drippers. This caused a reduction in the density of the plants. Even so, yield components, except shoot dry weight per meter (cob yield per plant and per meter, and shoot dry weight per plant) increased with the Agrosoak application rate. Concentrations of nitrogen and sodium in the leaves increased, but phosphate and potassium were unaffected by the Agrosoak application rate with the use of fresh water or brackish water. The use of Agrosoak did not avoid salinity damage to the plants. The results show that the use of trickle irrigation with PAM soil conditioner require a reevaluation of the method of irrigation.

INTRODUCTION

Sand dunes are characterized with a low water storage capacity especially when cultivated under arid conditions. All agricultural crops should be sub- jetted to frequent irrigation using expensive irrigation systems such as sprin- kling or trickling, or the irrigation may be inadequate. Even by use of these means, plants might suffer from a temporary shortage of water due to fast percolation of water deep below the root zone. The use of gel-forming hydro-

Correspondence to: M. Silberbush, Ben-Gurion University of the Negev, Jacob Blaustein Insti- tute for Desert Research, Desert Agrobiology Center, Sede Boker Campus 84993, Israel.

304 M. SILBERBUSH ET AL.

philic polymers to increase water holding capacity of sandy soils has been tested for many years. The polyacrylamid (PAM) is one of the most investi- gated groups (Azzam, 1980). These materials appear to be the most efficient water absorbents that prevent short-term wilting of plants. Their biodegra- dation in the soil is rather slow (Johnson, 1984, Baasiri et al., 1986). The limiting factor for wider use of these materials is their high cost. Under cer- tain conditions and by use of agrotechniques, their use may, however, become economical (Azzam, 1980).

In a series of tests, we studied the PAM "Agrosoak" (Agrosoak ® is manu- factured by Agropharm Ltd., Buckingham House, Church Road, Penn, High Wycombe, Bucks, HP10 8LN England, UK) as a potential soil conditioner for use on sand dunes. Unlike many other soil conditioners which are applied as emulsions, Agrosoak is produced in pellet form and does not coat the soil particles and aggregates. The present paper presents a field study for deter- mining the optimal amount of Agrosoak to be used in the soil and the com- bined effect of Agrosoak and the water salinity on the growth of corn irrigated by trickling. An extension of this study that includes another crop using a different irrigation method is reported in Part II.

MATERIALS AND METHODS

Field experiments were conducted on a desert sand dune soil (Typic Tor- ripssament) at the Ramat-Negev Experiment Station, Israel (30°57'N, 34 ° 38'E). The soil.texture was fine sand with:about a 7% lime content and about 2% eolian dust-originated sili. The experiment was designed as a fac, torial array using four amounts of Agrosoak (0.00, 0. t5~ 0.30 and 0.45% by weight in the upper 25 cm of the soil), three amounts of water (70, 85 and 100% of the recommended Class A evaporation pan coefficient), and two water salinity levels ( 1.2 and 6.5 dS-m- l ), in four randomized blocks. Each block was divided into six main plots in which combinations of water salinity and quantity were applied. The main plots were further randomly divided into four secondary plots, in which the Agrosoak treatments were applied. The set-up of the plots, with respect to Agrosoak treatments and water quan- tity and quality, is illustrated in Fig. 1. The dimension of the main plots were 4 x 20 m, each irrigated with four trickling lines with drippers spaced 0.5 m along the line with a capacity of 2 1- h - ~. Each main plot was further divided into four subplots, each consisting of 4 × 5 m, where the Agrosoak was evenly applied by hand and mixed into the upper 25 cm of the soil by use of a rotary plough. In addition, 16 plots were treated with 0.3% Agrosoak, of which eight were randomly selected and a 10 cm layer of sand was placed on top of the Agrosoak-treated layer. The remainder were left uncovered. Four plots of either the "covered" or "uncovered" treatment were irrigated with fresh water and four with brackish water.

USE OF HYDROPH1LIC POLYMER 1. CORN IRRIGATED BY TRICKLING 305

IlL _J 1 4 24 $0/W3 $O/WI SI/W3 81/1tl2 $0/W2 $1/WI

I [ I I ~ .J . . .~BLOCK 4

I ,I_I I l

T I II''''' ' I I I l_J---- BLOCK3 ',',::',', r, ® @ @

---~IIIII'III 86 @@@@@@

- " ® e e e e e

= = o w _ _ . 1 4 1

Fig. 1. Layout and setup of the experimental field with detailed arrangement of Block 1 as an example. So and St represent water with electrical conductivity of 1.2 and 6.5 dS-m- t , respec- tively; Ao, At, A2, A3 represent 0.00, 0.15, 0.30, 0.45% Agrosoak content in soil, respectively; W i, W2; W3 refer to 70, 85, 100% of the recommended irrigation water amount, respectively. The 16 plots on the left are the A2 treatments, covered/uncovered with untreated sand. For more details see text.

Cbrn (Zea~mays L cv. "i~azeraH,713" ) seedswere sown on J u l y | 0 , 1988, six plants per,m in fourrows along each pJot and 1 m between the rows. Each row was trickle-irrigated by a dripping line. Fresh water was applied by daily sprinkling to promote germination and amended with 60 kg- ha-~ ammo- nium sulfate. After the first initial 10-day period, irrigation by trickling was applied every 4 days. A complete liquid fertilizer (4.3% ammonium-N, 3.0% nitrate-N, 1.4% K, 0.87% P+micro-elements) was applied to the irrigation water. Iron (0.4 g Fe-EDDHA ha -I ) was applied once a week. The amount of water and nitrogen applied during the growth period is presented in Table 1. The other nutrients were applied according to their proportion to.N in the liquid fertilizer. In addition, 1000 kg.ha-1 super phosphate was mixed into the upper soil layer prior to the experiment.

Plant height, plant stand density, and leaf water potential measured by the pressure cell method (Scholander et al., 1965) were taken during the growth season. Soil moisture profdes were measured with a neutron probe moisture detector around the emitter and plants. Soil samples were taken before and after experimentation to-determine effect of the treatments on soil salinity. Some rows were severely damaged by porcupines during the early stages of the experiment. This problem was satisfactorily solved by installation of an

306 M . S I L B E R B U S H E T A L .

TABLE 1

Class A evaporating pan coefficient and nitrogen fertilization rate which were applied to corn throughout the growth season (based on recommendations of the Israeli Extension Service for the Ramat-Negev region, Israel

Days from Average daily Recommended Nitrogen sowing evaporation Class A Pan fertilization

( m m - d - l ) coefficient ( k g . h a - l . d - i )

11-22 9.5 0.6 1.0-2.5 22-31 10.0 0.9 2.5 32-41 8.8 0.9 5.0 42-52 8.3 0.9 5.0 53-63 7.8 1.2 7.0 64-71 8.1 1.2 7.0 72-83 8.7 0.9 2.0 84-91 7.3 0.9 2.0

50.

40.

3 0 .

2 0 .

10'

0 ~

A L E G E N D

t:l Dunng imgatlon • 48 hrs

+ 24 hrs ~ 7 2 hrs

• , | T • | ) m 15 25 35 45 55 65 75 85 95

D e p t h (cm)

5O

20"It ~ J

10"

0 15 25 35 45 55 65 75 85 95

D e p t h (cm)

Fig. 2. Water content distribution below a dripper on a trickle-irrigated sandy soil 0, 1, 2 and 3 days after irrigation. (A) untreated soil, and (B) mixed with 0.45% Agrosoak (symbols as in Fig. l ).

USE OF HYDROPHILIC POLYMER I. CORN IRRIGATED BY TRICKLING 307

electric fence operated by a lead buttery which was recharged by solar cells. On September 15, the fully-expanded youngest leaves were sampled and ana- lyzed for P, N, Ca and Mg after digestion with H2SO4+H202, K, Na and C1 were determined in hot water extracts.

The experimental crop was harvested on October 18, 1988. Corn cobs and shoots were cut along a 2-6 m length (depending on the extent of damage caused by porcupines) from the two middle rows of each plot. Fresh weight and dry weight (60 ° C ) for the shoots and cobs were measured. Soil cores ( 8 cm in diameter) in a vertical increments of 10 cm were taken 0, 15 and 30 cm from an emitter to a depth of 50 cm. The sand was washed from the roots using a 0.5 m m screen and their length and density were measured by the line- intersect method (Tennant, 1975 ).

RESULTS

Water content distribution in the soil below a dripper is presented in Fig. 2 for untreated (A) and 0.45% Agrosoak (B), respectively, on the first, second and fourth days after irrigation. Agrosoak increased water storage in the soil, but most of the water remained in the vicinity of the emitter and did not overlap the commonly-practiced 50 cm distance between the drippers as shown in Fig. 3. Figure 4 shows that the root length density distribution (RLD) followed the pattern of the water distribution. Without Agrosoak the

~/¢ mtusture (w/w) '7~ moisture (w/w) 3-D Moisture Profile ~ 0.,.8., .16 0.,. ,8., .1.6.. 74., 32

(},.8 ..16. 0.,.8,.,,16

Xx, X ~ X X X X ~ ~ ![ CISampling location i[ -25 :6 Emitter i~-20 -- Dripping line

l:50 ',,['-5 A O BI~ l.Om

°

Fig. 3. Moisture distribution in sand treated with 0.45% Agrosoak 2 days after irrigation.

308 M. SILBERBUSH ET AL

ROOT DENSIT'I / ZORN TRAEATEMENT AO

DISTANCE ( c m ; _ 'Z, 4 8 ~ lh 12 15 20 24 28 52 36 40 44 48

, ~.., w , . ; -4 . , \ t , , . t ' , l v , . i / l t , / , i , l , , ~ i~ . . . . . A . ~ . ~ - -. . ~ 1 / ' ,, ,,,, /

i i I I 1~----. ~ 16 ~ "

_J

z" -

ROOT DENSIT"¢ / CORN TREATEMENT A2

DISTANCE ( c m )

o'i,,v\~jy),>, "0 ~)//i I' i'~' ':' 7 ' '" \ ~'---._~,o144..r-----__m~%ti,I ~ ~ \

o

-2o (

/ / -25 i-- .../"

I i "

-30 ~/

-35 i ~ ~ ,0L/"

J . / \ \ \ \

Fig. 4. Distribution of root length density (cm-cm -3 of soil) in the soil irrigated by a dripper in (A) untreated and (B) with 0.30% Agrosoak. Closed circles indicate the position of emitters.

USE OF HYDROPHILIC POLYMER I. CORN IRRIGATED BY TRICKLING 309

TABLE 2

Effect o f the Agrosoak content in the soil on plant densi ty and corn yield. Means with different letters are significantly different (p < 0.05) according to the Least Significant Difference Test (LSD)

Agrosoak Plant densi ty Shoot dry weight Cob dry weight (%) (p lan t s -m - t )

(kg .m - I ) (g-plato - l ) ( g .m - I ) (g .p lant - I )

0.00 5.85" 1.02" 175 ¢ 617 b 79.8 ¢ 0.15 5.89" 1.07" 181 ¢ 638 b 821 b,¢ 0.30 5.02 b 0.90 b 192 b 652 "b 91.6 b 0.45 4.09 ~ 0.83 ~ 207" 731" 102.0"

TABLE 3

Different yield indices for corn as affected by different water amount and salinity; average results for all Agrosoak t rea tments (wi th in each column, means with different letters are significantly different ( p < 0 . 0 5 ) according to LSD)

R e c o m m e n d e d EC Shoot dry weight Cob dry weight irrigation (%) ( d S - m - t )

( k g . m - l ) (g-plant - l ) (g -m -2 ) (g .p lant - t )

70 1.2 1.07 b 201b'c 708 c 92.3 b 6.5 0.63 d 130 e 4 5 8 f 54.6 d

85 1.2 1.23 a 212 b 750 b 105 b 6.5 0.73 c'a 149 d'e 526 c 68.6 ~d

100 1.2 1.23" 259 ~ 914 ~ 132.0- 6.5 0.81 ~ 171 ¢.d 605 d 85.9b,c

TABLE 4

Mineral content in corn leaves grown with different water salinities in response to Agrosoak content (wi thin each column, means with different letters are significantly different ( p < 0 . 0 5 ) according to LSD

EC Agrosoak N K Na C1 ( d S - m - l ) (%)

(retool- k g - l dry weight )

1.2

6.5

0.00 1529 ¢ 481 ¢ 31 e 255 ¢ 0.15 1675 b'c 503 b'c 53 d'e 230 c 0.30 1742 b 512 b'¢ 53 a'~ 249 ¢ 0.45 1824 "b 513 b 60 d 250 ¢

0.00 1601 b.e 558" 113 ¢ 396 a'b 0.15 1646 b'~ 51 I b'c 167 b 362 b 0.30 1857 ~'b 498 b'¢ 208" 393 "b 0.45 1955" 503 b'¢ 224" 421 a

310 M . S 1 L B E R B U S H E T A L .

3 0 0

2 0 0

1 0 0 -

O

0 O

o o/j-

Y = 5 2 4 5 X + 4 4 9 4

r = O 8 6 5

, , , , , J . i , i , i , r , i , J • i , , , , , i , i , i , 0 0 1 5 0 3 0 0 4 5

A P P L I E D A G R O S O A K ( % )

Fig. 5. Concentrations of Na on a 1 : 1 ratio for the soil-water extract with different contents of Agrosoak in the soil.

RLD was higher and more extensively distributed. With Agrosoak roots ac- cumulated mainly in the treated soil layer with smaller RLD values.

The analysis of variance for the different indices of the corn yield resulted in a very significant effect for most of the indices measured. Agrosoak had a negative effect on plant density (Table 2) probably due to water accumula- tion at the vicinity of the dripper, while the space between the emitters re- mained relatively dry. This also caused death to some of the plants. This ef- fect was also reflected in shoot dry weight per meter of plants. However, when expressed in gram per plant, the effect of Agrosoak was reversed: the higher the Agrosoak mixing ratio the larger the plants (Table 2). Cob yield was pos- itively correlated with the Agrosoak amount, either when expressed as gram per meter row or per plant. The compensation in cob yield, as an adjustment to varied plant density, is familiar in corn growth (Tetio-Kagho and Gardner, 1988). Average effects of water amount and salinity over all Agrosoak treatments on different indices of yield are presented in Table 3. A positive effect for water amount and a negative effect for water salinity on plant yield were obtained from all the yield indices.

Concentration of mineral elements in the leaves just before tasselling is pre- sented in Table 4. No differences were obtained from treatments in the P, Ca and Mg concentrations in the leaves according to the analysis of variance and no significant effect of water amount on leaf mineral concentration was de- tected. Compared to fresh water, the leaf Na concentration doubled in plants grown with brackish water. Furthermore, in either water qualities leaf Na was correlated with the percentage of Agrosoak in the soil. However, the leaf CI

USE OF HYDROPHILIC POLYMER I. CORN IRRIGATED BY TRICKLING 311

concentration was affected only by the water salinity and not by the Agrosoak treatment. The nitrogen concentration increased with the treatment of Agro- soak as did the K content, but only in fresh water. The cause for the Na in- crease in the leaves with the Agrosoak percentage may be seen in Fig. 5. The Na concentration in the 1:1 soil-water extract was correlated with the Agro- soak percentage in the soil, which indicated that Na originated not only from the saline water but from the Agrosoak as well.

DISCUSSION AND CONCLUSIONS

The agricultural benefits of Agrosoak were tested for: ( 1 ) to increase the water holding capacity of sand dunes; (2) to increase the water available to the crop; and (3) to reduce water losses by deep drainage. From these points of view, the use of Agrosoak was successful. The irrigation cycle lasted twice as long as usually practised in this region for sand dunes. However, the use of trickle irrigation should be reconsidered for this scheme. With spaces of 50 cm between the drippers (which is common practice in sandy soils), water accumulated in the Agrosoak gel in the vicinity of the emitters (Fig. 3), and the plants between the drippers died due to insufficient supply of water. The plants located next to the drippers, however, grew well and their yield was well correlated with the rate of Agrosoak in the soil. Furthermore, the rela- tively low density of plants was compensated by a higher cob yield. There is, however, no guarantee that such compensation would occur with other crops. The effect of Agrosoak should be considered as a limitation for such irrigation system. Drippers placed close together or a "sweating" pipe may provide a better means for irrigation. Alternatively, when Agrosoak is evenly distrib- uted, the moisture absorbing capacity of the soil should increase to an extent which may enable the use of the common sprinkler irrigation with a reasona- ble efficiency. This approach was later tested in the same experimental field with cabbage in the growing winter season. Description of the experiment and the discussion of results are presented in Silberbush et al., this issue).

Corn plots which were irrigated with saline water (6.5 dS-m -~ ) were poorly developed, especially when irrigated with reduced water amounts. It was ob- served, however, that low water amounts with high Agrosoak concentration helped the corn plants to grow better and to produce a relatively higher yield per plant (Table 3). On the other hand, plots irrigated with fresh water ( 1.2 dS.m -~ ) exhibited retarded growth rates with increased Agrosoak applica- tion rates during the early growth stages. This suppression was more pro- nounced in the reduced water amount (70%). The picture completely changed, however, towards the final growth stage when a higher Agrosoak percentage compensated for the shortage of irrigation water while an increased supply of water was needed. It was also observed that Agrosoak water absorbence ca-

312 M. SILBERBUSH ET AL.

pacity, as with all polymers of this type, is decreased with increasing of water salinity.

Plant root systems were condensed in the Agrosoak-treated soil. This pro- vided a better water supply to the plants and, consequently, a better growth and higher yields. Apparently the best results were obtained by the combina- tion of the recommended amount of water and 0.2% Agrosoak in the upper 25 cm soil profile.

Leaf analysis revealed that the major problem with Agrosoak as an agricul- tural soil conditioner is the release of Na into the soil solution. This particular material was not developed for agricultural purposes, but was originally cre- ated as a moisture absorbing agent in various products. However, neutrali- zation by a strong base (NaOH), after the acidic polymerization, loaded the polymer pellets with Na. Agrosoak, having a high water absorbing capacity but without the contamination of Na, may serve as the most effective condi- tioner for irrigated sand dune soils under arid conditions. Related to the in- sufficient soil water distribution with trickle irrigation we assumed that the negative effect of sodium was enhanced by stress of water between drippers. Therefore, the same field was tested with sprinkling irrigation with variable quantity and quality of water application. Results are described in Silberbush et al., this issue).

ACKNOWLEDGEMENTS

The project was supported by the National Council for Research and De- velopment; Ministry of Science and Technology and the Water Commission, Israel. The contribution of Agrosoak ® made by Derech Ltd., Tel Aviv, Hard- ene Ltd., London, and Agropharm Ltd., England, is most appreciated.

REFERENCES

Azzam, R.A.I., 1980. Agricultural polymers: Polyacrylamide preparation, application and pros- pects in soil conditioning. Commun. Soil Sci. Plant Anal., 1 l: 767-834.

Baasiri, M., Ryan, J., Mucheik, M. and Harik, S.N., 1986. Soil application of a hydrophilic conditioner in relation to moisture, irrigation frequency and crop growth. Commun. Soil Sci. Plant Anal., 17- 573-589.

Johnson, M.S., 1984. The effect of gel-forming polyacrylamides on moisture storage in sandy soils. J. Sci. Food Agric., 35:1196-1200.

McGuire, E., Carrow, R.N. and Troll, J., 1978. Chemical soil conditioner effects on sand soils and turfgrass growth. Agron. J., 70:317-32 I.

Scholander, P.F., Hammel, H.T., Brandstreet, E.D. and Hemingsen, E.A., 1965. Sap pressure in vascular plants. Science, 148:339-346.

Silberbush, M., Adar, E.M. and De Malach, Y., 1992. Use of hydrophilic polymer to improve water storage and availability to crops grown on sand dunes. II. Cabbage irrigated by sprin- kling with different water qualities. Agric. Water Manage. (this issue).

USE OF HYDROPHILIC POLYMER L CORN IRRIGATED BY TRICKLING 313

Stewart, B.A. (Editor), 1975. Soil conditioners. SSSA Spec. Publ. No. 7. American Society of Agronomy, Madison, WI, USA.

Tennant, D., 1975. A test of a modified line intersect method of estimating root length. J. Ecol., 63: 995-1001.

Tetio-Kagho, F. and Gardner, F.P., 1988. Responses of maize to plant population density. II. Reproductive development, yield, and yield adjustments. Agron. J., 80: 935-940.