Vol.2, No.4, 544-550 (2011)
opyright © 2011 SciRes. Openly accessible at http://www.scirp.org/journal/AS/
Agricultural Scienc es
Hydrogel amendment to sandy soil reduces irrigation
frequency and improves the biomass of Agrostis
Hillary Agaba1*, Lawrence J. B. Orikiriza2, Joseph Obua3, John. D. Kabasa4, Martin Worbes5,
Aloys Hüttermann6
1National Forestry Resources Research Institute, Kampala, Uganda; *Corresponding Author: hiagaba@yahoo.com
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.
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
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
Copyright © 2011 SciRes. Openly accessible at http://www.scirp.org/journal/AS/
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,
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
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
Copyright © 2011 SciRes. Openly accessible at http://www.scirp.org/journal/AS/
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-
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.
3.1. 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
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)
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
Copyright © 2011 SciRes. http://www.scirp.org/journal/AS/
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).
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
Copyright © 2011 SciRes. Openly accessible at http://www.scirp.org/journal/AS/
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
4.1. Effect of Hydrogel Amendment on
Irrigation Frequency, Root Biomass
and Water Use Efficiency of Agrostis
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
The implication of this study as far as plantation for-
H. Agaba et al. / Agricultural Sciences 2 (2011) 544-550
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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.
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.
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-
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