Hydrogel amendment to sandy soil reduces irrigation frequency and improves the biomass of Agrostis stolonifera

doi:10.4236/as.2011.24071

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Vol.2, No.4, 544-550 (2011)

doi:10.4236/as.2011.24071

Agricultural Scienc es

Hydrogel amendment to sandy soil reduces irrigation

frequency and improves the biomass of Agrostis

stolonifera

Hillary Agaba1*, Lawrence J. B. Orikiriza2, Joseph Obua3, John. D. Kabasa4, Martin Worbes5,

Aloys Hüttermann6

1National Forestry Resources Research Institute, Kampala, Uganda; *Corresponding Author: [email protected]

2Department of Forestry, Biodiversity and Tourism, School of Forestry, Environmental and Geographical Sciences, Makerere Uni-

versity, Kampala, Uganda;

3Interuniversity Council of East Africa, Kampala, Uganda;

4School of Veterinary Medicine Makerere University, Kampala, Uganda;

5Department for Crop Sciences, Tropical Agriculture Universität, Göttingen, Germany;

6Institute of Forest Botany, University of Goettingen, Goettingen, Germany.

Received 8 September 2011; revised 15 October 2011; accepted 26 October 2011.

ABSTRACT

Soil water potential indicates the w at e r status of

the soil and the need for irrigation. The effect of

hydrogel amendment to the upper sand soil layer

on water infiltration into the lower un-amended

sand layer, irrigation frequency, water use effi-

ciency and biomass production of Agrostis stolo-

nifera was investigated. The upper 25 cm sand

layer in three identical buckets was amended at

0.4%, 0.2% and a control (no hydrogel) while the

lower 25 cm sand layer separated from the up-

per layer by a wire mesh in the same buckets

was un-amended. Agrostis stolonifera seeds

were sown in each bucket and adequately irri-

gated using a hand sprayer. Potential meter

electrodes were inserted at three random posi-

tions in each of the buckets and subsequent

irrigations were done when a pressure of 600

bars was recorded in any of the three t reatments.

Data were collected on irrigation frequency, water

content in the lower layer, water use efficiency

and biomass production of Agrostis stolonifera.

The mean water potential in the lower 25 cm

layer un-amended sand was significantly more

negative in the 0.4% hydrogel than in the control.

More water content (10%) was recorded in the

lower layer under the control bucket than in ei-

ther the 0.2% and 0.4% hydrogel amended buck-

ets. The frequency of irrigation was three-fold in

the control compared to the 0.4% hydrogel

amended sand. The h ydrogel amende d sand sig-

nificantly increased the shoot and root biomass

of Agrostis stolonifera by 2.2 and 4 times re-

spectively compared to the control. The 0.4%

hydrogel amendment in sand increased the

water use efficiency of grass eight fold with re-

spect to the control. The hydrogel stimulated

development of a dense root network and root

aggregation that increased contact of the roots

with moisture thus improving water use effi-

ciency of hydrogel amended soil. The results

suggest that hydrogels can improve sandy soil

properties for plant growth by absorbing and

keeping water longer in the soil matrix thus re-

ducing watering frequency.

Keywords: Sand; Water Use Efficiency; Hydrogel;

Irrigation; Biomass; Agrostis Stolonifera

1. INTRODUCTION

Moisture retention in the soil is fundamental in plan-

tation forest establishment [1-3]. Soil water affects plant

growth directly because it influences aeration, tempera-

ture, nutrient transport, uptake and transformation [4].

Large pore spaces in sandy soils prevent water retention,

make water dry out easily and escalates leaching of pre-

cious nutrients past plant roots [1], thus hindering plant

growth. There have been claims though, that addition of

crosslinked polyacrylamide hydrogels to sandy soils

reduces the rate of water percolation while increasing the

water availability to plants [5].

The amount of soil water is usually measured in terms

of percentage by volume or mass [6] or as soil water

potential. Water content does not necessarily imply the

H. Agaba et al. / Agricultural Sciences 2 (2011) 544-550

545545

availability of water to plants, nor does it indicate how

the water moves within the soil profile but rather, it is

the relative amount of water in soil. Soil water potential,

which is the energy required to remove water from the

soil, does not show the amount of water present in the

root zone [4]. Therefore, soil water content and soil wa-

ter potential should be considered when planning irriga-

tion and taking measures to improve plant growth [4].

Hydrophilic polymers potentially influence infiltration

rates, density, soil structure, compaction, soil texture,

aggregate stability, crust hardness [7], and evaporation

rates [8]. They increase the plant available water in the

soil which prolongs plant survival under water stress

[2,9,10]. While irrigation is critical in overcoming water

stress, the timing (which includes measurement of soil

water, estimation of loss by evapo-transpiration, and

measurement of plant water status) is important [4,11,

12]. The low water holding capacity of sand soil causes

rapid infiltration and deep percolation below the root

zone. The use of gel-forming hydrophilic polymers (hy-

drogels) has been tested for some years and found to

increase the water holding capacity of sandy soils [13,

14].

High water infiltration in sandy soils has been ob-

served to lead to deep percolation and inefficient fertil-

izer and water use thus posing a significant problem in

arid and semi arid regions [1]. Super Absorbent Poly-

mers (SAPs) can store water in the upper horizons of the

soil where plant roots are found. Significant reductions

in irrigation requirements of many plants due to an in-

crease in water holding capacity by hydrogel-amended

soils have been reported [13]. Soil water potential shows

the water status of soil and the need for irrigation. At

both high (360 L/m2) and low (36 L/m2) irrigation

speeds, [2] demonstrated that soil moisture was higher in

the upper than lower horizons of soils amended with

hydrogels after two weeks. Conventional irrigation usu-

ally experiences the problem of losing a significant por-

tion of the water to the aquifer [15,16]. As noted above,

super absorbent hydrogels increase water storage of soils

in the upper horizons of the soil thereby saving water

and labor requirements in irrigation due to reduced irri-

gation frequencies. The overall objective of this study

was to examine the effect of hydrogel amendment to the

upper sand soil layer on water uptake by that layer, irri-

gation frequency and water availability for the growth of

Agrostis stolonifera, a grass species commonly used in

golf courses. The specific objectives were to 1) deter-

mine the influence of hydrogel amendment on biomass

development of Agrostis stolonifera under water poten-

tial controlled irrigation timing and 2) determine the

effect of hydrogel amendment to the upper sandy soil

layer on water infiltration into the lower un-amended

sand layer. The following hypotheses were tested: 1)

Hydrogel amendment to sand has no effect on the bio-

mass of Agrostis stolonifera, 2) Hydrogel amendment to

the upper sand layer does not reduce water infiltration

into the lower un-amended layer and 3) Hydrogel amend-

ment does not affect irrigation frequency and saves no

water during growth of Agrostis stolonifera. Agrostis

stolonifera (bent grass) was traditionally confined almost

entirely to golf greens. Now many homeowners prefer

bentgrass lawns because of their beautiful carpet like

turf.

2. MATERIALS AND METHODS

2.1. Materials

The materials used in this experiment were Grass

seeds (Agrostis stolonifera) luquasorb hydrogel, three

identical plastic buckets measuring 51 and 41.3 cm top

and lower diameters respectively, and 50 cm in height

(Volume 83,595 cm3) and a potential meter (DMG 900)

for measuring water potential in cm bars. The sand was

obtained from a sand pit in Schoningen in the Solling

mountains close to Goettingen. Luquasorb hydrogel

manufactured by the BASF SE Chemical Company,

Ludwigshafen, Germany was used as the soil amend-

ment at the following concentrations: 0 (as control),

0.2% and 0.4%. The 0.2% and 0.4% hydrogel concentra-

tions were made by mixing 2 and 4 kg of hydrogel pow-

der respectively with 1000 kg of soil in a concrete mixer

(Mini Concrete Mixer, Model: CM 180 - MZ2; Mixing

capacity 180 L). The control had no hydrogel added. The

amount of hydrogel used and the mixing procedures

were according to [6,17]

2.2. Methods

The experiment was conducted in a glass house set up

at a temperature range of 25˚C - 32˚C and relative hu-

midity of 50% - 95%. The three identical buckets were

weighed and filled with sand to the 25 cm mark from the

bottom of each bucket, and a wire mesh placed on top of

this sand layer. The remaining top 25 cm layer in each

bucket was then filled with sand amended with 0 (Con-

trol—no hydrogel), 0.2% and 0.4% hydrogel and labeled

accordingly. Using a water sprayer (Trigger sprayer, ca-

pacity 1.5 litres—Spray flow: 240 ml/min), the buckets

were irrigated until full saturation. Any water collecting

on the surface was allowed to fully infiltrate. The

weights of the fully irrigated buckets were recorded on a

Sartorius scale. About 200 g of Agrostis stolonifera grass

seeds were then sown in each bucket containing the

various hydrogel treatments (control, 0.2% and 0.4%) by

uniformly sprinkling them on the surface of each bucket

H. Agaba et al. / Agricultural Sciences 2 (2011) 544-550

546

and covering with a thin layer of sand. Water potential

meter electrodes were then inserted at three random po-

sitions into the top sand layer in each bucket. The water

potential was monitored and recorded daily using a po-

tential meter (DMG 900) and whenever it recorded –600

cm bars, the bucket and its contents were weighed to

determine how much water had transpired, and subse-

quently irrigated until the pressure as recorded by the

potential meter dropped to 0 cm bars. The added water

was recorded, and monitoring of the rise in pressure

continued for 10 weeks till the grass had fully grown.

After the Agrostis stolonifera grass had fully grown

(10 weeks), the buckets were divided into 4 quarters to

make four replicates for each bucket. From each quarter,

the grass together with the sand mass containing the

roots was scooped up to the 25 cm depth using a small

hand shovel. The roots were then washed gently under

tap water and then separated from the grass shoots by

gently cutting with a pair of scissors. Fresh weight of

shoots and roots samples from each quarter was recorded

using an electronic Sartorius weighing scale (Model ED

8201—CW). The root and shoot samples from each

quarter in respective buckets were first sun dried and

later oven dried at 65˚C until a constant weight was at-

tained.

Water use Efficiency was calculated from the ratio of

total dry mass (shoot and root) of the grass and the amount

of water transpired during the experiment. Transpired

water was estimated from the difference in weight of the

buckets after complete infiltration was attained at plant-

ing time and the weight at subsequent irrigations till the

time of harvesting the grass. This measurement was ac-

cording to [18].

One-way analysis of variance (ANOVA) of SPSS 11.5

software (SPSS Inc., 2002) was used to analyze the ef-

fect of hydrogel levels on water uptake by the upper soil

layer, water content in the lower sand layer and root and

shoot biomass production of Agrostis stolonifera. Dif-

ferences between means of shoot and root biomass were

confirmed by Tukey HSD test, and mean differences

were regarded significant at p ≤ 0.05.

3. RESULTS

3.1. Water Potential and Water Content

The results of water potential and water content in the

lower layer of sand un amended with hydrogel in the

three experimental buckets are presented in Figures 1

and 2. The mean water potential in the lower 25 cm layer

un amended with hydrogel was significantly more nega-

tive (F(2,9) = 11, p = 0.003) in the 0.4% hydrogel

amendment than in the control implying that less water

had infiltrated into this layer (Figure 1). Similarly, water

content in the lower 25 cm sand layer for the control was

double that in the 0.4% hydrogel amendment (Figure 2).

3.2. Irrigation Frequency and Water Use

Efficiency

The watering/irrigation frequency (Table 1) and water

use efficiency (Ta bl e 2) of the grass lawn show that the

0.4% hydrogel amendment required watering only once

during the 69 days of growth compared to the control

that was irrigated three times in the same period. Less

water (9 litres) was applied in the 0.4% hydrogel amended

soil and produced more grass biomass (both shoot and

root than the control which was irrigated three times

(Ta b l e 1 ) with more water (Ta ble 2) and produced less

biomass (Figure 3).

Hydrogel concentration

Bars (cm)

–10

–20

–30

–40

–50

–60

–70

–80

–90

Figure 1. Water potential in the lower un amended 25 cm

depth of sand immediately after harvesting the grass in

the buckets.

Hydrogel concentration

% Water content

Control 0.2% 0.4%

Figure 2. Water content in the lower unamended 25 cm

layer of sand in the three buckets with top 25 cm sand

layer amended at 0%, 0.2% and 0.4% hydrogel grown

with Agrostis stolonifera grass.

H. Agaba et al. / Agricultural Sciences 2 (2011) 544-550

547547

Table 1. Frequency of irrigation, weight of bucket for the various treatments at planting till harvesting of the Agrostis

stolonifera grass and estimated transpired water during 69 days of growth. Subsequent irrigations in each treatment were

initiated after attainment of –600 cm Bars measured by the Potential meter.

Bucket weight (kg)

Point of measurement Control 0.2% hydrogel 0.4% hydrogel

Before 1st irrigation 85.4 86.2 85.8

After 1st irrigation 91.4 95.2 94.8

Before 2nd irrigation 85.9 87.1 -

After 2nd irrigation 94.9 96.1 -

Before 3rd irrigation 87.9 - -

After 3rd irrigation 96.9 - -

At harvest of the grass 95.1 95.8 94.2

Transpired water (Litres) 24.0 18.0 8.4

Ta ble 2 . Amount of water used, shoot and root biomass produced and calculated water use efficiency of Agrostis stolo-

nifera grass in sand soil amended with hydrogel.

Treatment Water used in 69 days (L) Shoot and root biomass (g) Water Use efficiency (g/L)

Control 24 37.8 1.56

0.2% hydrogel 18 49.5 2.75

0.4% hydrogel 8.4 125.7 13.7

4. DISCUSSION 3.3. Effect of Hydrogel Amendment on

Grass Shoot and Root Biomass

Production In this study the water use efficiency of the Agrostis

stolonifera grass increased by about 8 times compared to

the control (Figure 3). The grass grew for 69 days and

depended on the 9 litres that was applied at the start of

the experiment unlike the control and 0.2% hydrogel

amended soil that were irrigated more than once with 24

and 18 litres of water respectively during the same pe-

riod (Table 1). The ability of the hydrogel to retain water

and release it slowly could be the reason for improved

water use efficiency. As shown in Fiugre 4 root aggre-

gation of the grass around fragments of the gel avails

water to the roots for a long time thereby contributing to

adequate water needs for photosynthesis. These findings

are consistent with those of [3] who observed that appli-

cation of superabsorbent polymer at the rate of 0.6% in

loamy-sandy soil and 0.2% in sandy clay loam resulted

in the highest aerial and root biomass for corn. At these

polymer rates (0.6% in the loamy sand and 0.2% in the

sandy clay loam), the amounts of aerial and root biomass

for corn were 2.3 and 2.0 times greater than those of the

control in loamy-sand and 1.6 and 1.7 times that of the

untreated sandy clay loam soil, respectively. A greater

water use efficiency and dry matter production following

application of polymers in the growth media has been

reported by [19]. It is common knowledge that water

stress is one of the fundamental constraints to productive

use of land in the arid and semi-arid areas that perennially

Hydrogel application at 0.4% level significantly in-

creased the shoot (F(2,9) = 37.0, p < 0.001) and root bio-

mass (F(2,9) = 24.3, p < 0.001) of the grass by 4 and 2.2

times respectively compared to the control (Figure 3).

No significant increase in both root (p = 0.482) and

shoot biomass (p = 0.695) was observed in the 0.2%

hydrogel amendment compared to the control. The hy-

drogel further resulted in growth of a thick root network

(Figure 4).

Shoot

Root

w/w

rams

120.0

100.0

80.0

60.0

40.0

20.0

0.0

Control 0.2% hydrogel 0.4% hydrogel

Figure 3. Effect of hydrogel amendment on root and shoot

biomass of Agrostis stolonifera grown in sandy soil.

Openly accessible at

H. Agaba et al. / Agricultural Sciences 2 (2011) 544-550

548

Figure 4. Root biomass development of Agrostis stolonifera in both the control and 0.4% hy-

drogel amended soil.

experience low rainfall. Plant growth is impaired by lit-

tle or insufficient soil moisture [20]. According to [21]

one of the major economic consequences of insufficient

water in agricultural systems is yield reduction. De-

creased photosynthesis reduces biomass production and

results in decreased yields [21-26]. In addition, drought-

stress reduces carbon dioxide assimilation, stomatal con-

ductance and transpiration [21-26]. The above was re-

versed in this study due to adequate supply of water by

the gel to the grass roots especially in the 0.4% hydrogel

amendment.

4.1. Effect of Hydrogel Amendment on

Irrigation Frequency, Root Biomass

and Water Use Efficiency of Agrostis

Stolonifera

Amendment with 0.4% hydrogel limited irrigation to

only once up to the time of harvesting the Agrostis

stolonifera grass (Ta b l e 1 ), implying that enough water

was retained by the hydrogel and was available for

growth of the grass over the 69 days growth period.

Elsewhere, studies have shown that SAP amendments

can reduce soil penetration resistance [27], increase soil-

water holding capacity [6,10] and soil aggregation while

aiding the protection of soil organic matter [28,29].

Studies by [30] showed that hydrophilic polymer addi-

tion reduced irrigation frequencies without affecting the

growth of Photiniafraseri. Reduced water needs when

growing ornamental plants were also reported by [13,

31]. According to Sharma [32], plants growing in hy-

drogel-amended soil have more water available (re-

flected in higher stomatal conductance and higher leaf

water potential) for longer period of time than control

plants thus the frequency of irrigation may be reduced.

Increase in plant growth may also be due to increased

nutrient retention in hydrogel-amended substrate [33].

The 0.4% hydrogel amendment led to the develop-

ment of a dense root network (Figure 4) forming some

kind of root aggregation with gel fragments that soaked

the roots. Root aggregation allows good contact of roots

with the moisture source in the polymer and plays a ma-

jor part in improving water use efficiency of poly-

mer-treated growing systems. Root dipping with poly-

mer gels increases survival of transplants in drying soil

[6,34], and inevitably leads to good shoot development

as a result of adequate nutrient extraction. It is probable

that root dipping and root aggregation around fragments

of the gel have similar beneficial effects as both allow

better water use efficiency through increased root con-

tact with a source of water that is available to plants.

4.2. Implications in View of Plantation

Forestry

The implication of this study as far as plantation for-

H. Agaba et al. / Agricultural Sciences 2 (2011) 544-550

549549

estry is concerned is that even a thin soil layer contain-

ing a small amount of dry SAP can be able to pick up

virtually all rain falling down whereby enough water

will be retained and aid tree seedlings establishment in

arid areas. In Uganda, the first ever hydrogel application

for afforestation of degraded lands in Africa was con-

ducted in four sites namely Nakasongola, Kiruhura,

Mpigi and Mubende. Hydrogel was applied at a level of

20 and 40 g per planting hole, as well as a control. A

comparison of the survival of E. grandis across the four

sites showed significantly higher survival in the hy-

drogel amended plots than the control in three sites. Data

from field experiments in Uganda also indicate that SAP

amendments (either 40 or 20 g per plant hole) signifi-

cantly improved the growth and above ground biomass

of nine tree species (Eucalyptus grandis, Pinus caribaea,

Grevillea robusta, Eucalyptus camaldulensis, Maesopsis

eminii, Terminalia superba, Araucaria cunninghamii,

Azadirachta indica and Melia volkensii) planted in four

sites compared to the control (Orikiriza pers. comm.

2011).

Elsewhere in China, The most comprehensive field

experiments using hydrogels have been conducted by

[35] in the eroded areas of the drainage basin of the up-

per Jangtze River in Yunnan, which are barren hillsides,

heavily washed out by monsoon rains. Their studies

showed that the survival of trees was dependent on the

time span after planting and that almost 70% of the trees

growing on soils with the highest hydrogel amendment

survived after 19 months, whereas more than 80% of the

trees growing on the control soil died during that time.

The prolongation of survival of various plants (trees and

crops) in higher hydrogel amendment compared to con-

trol has been reported by some other authors [6,10,19].

The results have shown that the 0.4% hydrogel

amendment is effective in retaining water in the upper

sand layer in the buckets compared to either the 0.2% or

control. Irrigation frequency was reduced in the 0.4%

hydrogel leading to significant amounts of water saved

compared to the control. More biomass production of

Agrostis stolonifera was achieved with less water in the

0.4% hydrogel amendment, implying a high water use

efficiency of about 8 fold that of the control. This study

was conducted under controlled conditions, limited to

bucket sizes; and as such the outcomes under field con-

ditions may be completely different. It is recommended

that field applications in Uganda’s desert like areas be

conducted to explore the potential of hydrogels under

field conditions.

5. ACKNOWLEDGEMENTS

The financial and in-kind support provided for this study is grate-

fully acknowledged. Specifically, the support from KAAD (Katholischer

Akademicher Auslander Dienst) in Bonn (Germany) and the BASF-SE

Chemical Company in Ludwigshafen, (Germany) is highly appreci-

ated.

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