الفهرس 
Materials and mithodsOnly 14 pages are availabe for public view
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Abstract
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5. SUMMARY
Sandy soils have their own problems which can be assembled
in their single grain structure. high water requirements.
susceptibility to erosion and drought and loss of both
irrigation water and plant nutrients. Of the techniques that
can be applied to modify hydrophysical properties of sandy
soils and consequently improving plant-soil-water-fertilizers
relations in such soils is the use at synthesized SOlI
conditioners. Among these conditioners are super absorbent
materials (hydrogel). The present work aims at studying the
effect of such type of soil conditioners on hydrophysical
properties of sandy soils. Some economical crops-either
vegetables (Cucumber) or summer forage crops (Guar and Cowpea)
were chosen in this study as the indicator plants to clarity
the conditioning effect of hydrogels on quantities of
irrigation watr needed tor crop production from one side and
plant grwoth. yield and water and fertilizers use efficiency by
such crops on the other side. Therefore. the work was divided
into two parts. the first was conducted in the laboratory and
the greenhouse. while the other was in the field.
1- Effect of incorporating hydrog.l, in sandy 80il on its
hidrOphysicol properties (LaboratorY studies):
A Virgin sandy soil: (Sand - 94.8%. O.M.- 0.1%. CaC03 - 1.4%.
pH - 7.9) from EI-Shabab area. West Sinai. and hydrogel
[propenamide polymer with hydrophilic groups (BulphonatesJ
chemically crosslinked with a divalent Vinyl monomer tK salt)
”Evergreen 500-AustrianJ were used. The soil was treated wit.h
the hydrogel at different rates (0.0. 0.1. 0.15 and 0.2% W!W of
dry soil). Different indices were taken to evaluate the
improving effect of the conditioner on certain hydrophysical
and mechanical properties of the soil.
Obtained r.sult. could be summarized a. folloWS:
1.0) Soil structure in the dry state was improved with
increasing the amounts of hydrogel applied. Since soil
with non-erodible structural units )0.64 mm exceeding 60%
were considered as soil resistant to wind erosion and
break down by tillage. the treated soil with hydrogel at
0.2% seems to be the most stable treatment. It shows the
highest values of total and the most stable strcutural
units )0.84 rom. the destructive mechanical action
expressed by the number of rotations (W J or the time ot
dry sieving in minutes (t ) needed to return the
conditioned soil to its original stable state i.e. the
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control and the lowest values of wind erosion parameter.
instability parameter (SP) and deaggregation rate tRD).
b) The strucutre of sandy soil treated with the hydrogel 15
stable in the wet state. The stability increases with
application rate of the hydrogel. Water stable structural
units >0.5 mm and MWD of the size distribution of water
stable structural units reached 82.3% and 3.471%,
respectively. Relevant values for the untreated soil were
7.2% and 0.071, in sequence.
c) The formed structure maintained three cycles of complete
destruction and re-formation without remarkable changes in
either water stable structural units ) 0.5 rom or the
erosion index.
2. Whereas. the hydrogel decresed soil bulk density at
saturation and atter drying as well as the macro porosity.
it increased void ratio. total porosity, the micro pores
relative to the total or to the macro pores. Moacro:Micro
porosity reached about 1:1 by applying the hydrogel to
sandy soil at 0.2%. Water holding pores (28.8-0.19 u) were
increased by 46.8, 90.0 and 157.2% on the expense ot the
drainable pores (> 28.8 u) which decreased by 9.9, 18.4
and 34.5% relative to that of the control by treating the
soil with 0.1. 0.15 and 0.2% hydrogel, respectively.
3. Retained moisture in sandy soils, at all suctions under
study (from 0 to 15 bars) were increased by soil
conditioning being higher with increasing the application
rate of the hydrogel. Because the increase in water
retained in the soil at field capacity (pF- 2.01) is far
beyond that at wilting percentage (pF- 4.19), the
available water in the treated soil with 0.2% hydrogel was
increased to be about three times that ot the control
treatment. The decrease in air filled porosity ot the
conditioned soil is not likely to become limiting to plant
growth since the air filled porosity did not reach 10%.
4. The loss ot water from sandy soil through evaporation is
reduced by soil conditioning. Under the conditions of the
conducted experiments. the time required for saturated
soils to reach their wilting percentages were 10.5, 19.1.
24.3 and 28.0 days with average evaporatIon rates ot
2.086, 1.482, 1.251 and 1.057 mm day-1 tor the untreated
soil and that treated with 0.1, 0.15 and 0.2% hydrogel,
respectively. Regarding the intermittent evaporation
columns experiment. and for all of the eight successive
wetting and drying cycles, the conditioning treatments
could be arranged according to their effect on reducing
adjusted evaporation (Eadj) as tollows:
hydrogel 0.2% > hydrogel 0.15% ) hydrogel 0.1% > control.
The minor changes in the values of Eadj over the eight
cycles of wetting and drying reveal the stability of the
formed structure due to the conditioning process and the
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very low biodegradability of the examined hydrogel.
5. Values ot infiltration rate reveal the relatively high
’int i1tration’ rate of the untreated sandy soi 1 (: 0.85 em
min-i.”). Incorporating 0.1. 0.15. 0.2% hydrogels in the
soil lowered its infiltration rate by 10.6. 20.0 and
29.4%. respectively.
6. Incorporating 0.2% hydrogel in sandy soil decreases its
.mean pore d,iameter by· 31.9% and in turn its hydrau 1ic
conductivity decreases by 61.4% relative to those ot the
untreated soi 1.
1. The increase in soil mechanical strength of air dry soil-
.expressed by ·the unconfined compressive strength.
penetration resitance and the modulus of rupture - is not
so high to limit the use of such hydrogel at a rate of
0.2% tor sandy soil conditioning.
I’I-’Pie-lc.l.~•ucUe. on tbe effect of hYdrogel used .1 ::~i(;;;;;; for .andy 80il •. on the growth r.apons. and
. ’ ·;;;rtertii,tHnlll.e.tfici.ncY by 801DteconomiCAl
crog,:
’Experiment 1f
A completely randomized field experiment with four
replications tor each treatment was conducted in a vlrlgn sandy
soil at West Sinai to study the effect of two hydrogels namely
Evergreen 500 Austrian (polyacrylamide K sulphonate gel) and
DWAL (DOW. Water Absorbent Laminates) • American’ on
germination. plant growth. nutrients uptake and both water and
fertilizers use efficiency by the plants. Cucumber was chosen
as the indicator plant. Either the crystals ot the hydrogel
(Evergreen 500) at the rate of 4 g/plant pit or the laminates
’.ot the hydrogel (DWAL> at the rate of 0.24 rna/plant pit were
incorporated in the soil at a depth ot 15 em from the 8011
surtace. Controlled surface irrigation was applied at the rate
of 100 ~/fed/irrigation Ex~ined irrigation intervals were
~(normol irrigation). 8 and 12 days. All other agricultural
practices inclUding mineral fertilization were the same.
’;,’ObtaiDld,’ ’re_It., COUld be •• ,..rized II follO’tfll:
1- Addition of hydrogel to sandy soil enhances the
genuination process. The time needed for 50% emergence
(Teo) was reduced by 2;1 and 1.3 days with the hydrogels
Evergreen 500 and DWAL~ respectively.
2- Significant increases in plant height. number and area of
’leaves and the dry weight of plants were obtained by sandy
soil conditioning. Increments in the dry weight of plants
were aJDOunted to 121 and 85% tor DWAL. and 154 and 107.
for evervreen 500 over that of the control treatment at
the two irrigation intervals 8 and 12 days. respectively.
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3- Postive effects on the uptake Of N. P and K by Cucumber
plants were -achieved. Increments in nutrients uptake by
plants over that of the control arrived to be 187 and 93*
-for N. 181-· -and 155% for P ’and 109% for K when watering
the soil every 8 and 12 days. respectively.
”4- Usinghydrogels-as- conditioners for -sandy soi I markedly
raises its productivity. The increase in the yield of
--,Cucumber di-ffered ’by -the- type -of .’added hydrogel and
irrigation regime. Obtained yield increased by 37 and 21%
.tor DWALtreatments and 57% and 29% for Evergreen 500
treatments when the soil was irrigated every 8 and 12
days. respectively.
5- Applied materials resulted in a considerable reduction in
the water consumption and therefore a significant
improvement in the water use effeciency by plants was
obtained.- Increments in the water use efficiency by plants
expressed ’as kg of the marketable yield obtained by each
’cubic meter of the irrigation water used. compared to the
control treatment were 105 and 264% for DWAL and 136 and
288% for Evergreen 500 at the two irrigtion intervals 8
and 12 days. respectively.
6- The marketable yield obained trom conditioned sandy SOlI
by each unit of added nutrients refer to the beneficial
etfect of hydrogels on increasing the fertilizers use
efficiency by plants that ranged between 1.2 and 1.6 times
that of the untreated soil.
Experiment 2:
A ,two successive years completely randomized field
experiment with tour replications tor each treatment was
conducted at Salhia to stUdy the effect of treating virgln
sandy soils with hydrogels on yield and both water and
fertilizers use efficiency by Guar and Cowpea as of the main
summer forage crops. The used hydrogel in this experiment was a
polyacrylamide K SUlphonate gel (Evergreen 000. Austrian) at
the rates of 0.0. 33.3. 66.6° and 100 g/m~ soil. Controlled
surface irrigation was applied at the rates ot luu
m3/fed/irrigation. Examined irrigation intervals were 4 (normal
irrigation). 8 and 12 days. All other agricultural practices
including mineral fertilization were the same. The follOWing
parameters were determined; a) tresh and dry weight of the
obtained yield bJ water use efficiency by plants. and c}
tetilizers use efficiency by plants.
Obtained result. COUld be .’PPMrized a. tollOWWI
1- a- Fresh
positively
irrigation
increasing
and dry weights of obtained plants were
affected by gel treatments. Under the same
regime both fresh and dry weights incresed by
the application rate of the hydrogel.
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b- Doublling the irrigation intervals for the plants grown
in the treated soil with hydrogels has increased both the
fresh weights and the dry weights ot plants to reach
maximum when 100 g of the examined hydrogel/m~ soil was
applied.
c- Reducing the applied irrigation water to the third
resulted in a little decrease in the tresh and dry weIght
yields. However. the production was stIll much higher than
that under the control. In this case when 100 9 of the
hydrogel were added to each m~ of the soil. the increase
compared to the control treatment were 1~5 and o4~ tor the
tresh weight yield and 121 and 65% tor the dry one ot Guar
and Cowpea crops. respectively
2- a- Produced yield by the unit of either irrigation water
or added fertilizers refer to the beneficial effect of the
hydrogel for raising the productivity of sandy sOlI.
reducing water consumption and increasing both water and
fertilizers use efficiency by plants.
b- The highest water use efficiency value lies at 100g
hydrogel/rnasoil when the soil was irrigated every 12
days. This was about 5.8 and 4.8 times that of the control
treatment for Guar and Cowpea in sequence.
c- Fertilizers use efficiency by Guar produced in sandy
soil treted with 100 g hydrogel/m3 soil and irrigated
every 8 days has reached 2.25 times that of the untreted
soil irrigated every 4 days. ReleVant value for cowpea was
2.0 times.
Obtained results may prove the importance of using
hydrogels for conserving irrigation water and increasing crops
production of the sandy soils under the severe conditions of
our deserts. i.e.• the limited water resources and the
inadequate water retention and low fertility of these soils.
When evaluating the use of such products as conditioners for
sandy soils. one has to take in consideration the improvement
of the hydrophysical properties and the nutritional status of
the soil. the increase in the yield and the saving costs of the
irrigation water and fertilizers on one side and the costs of
the product itself and costs of the conditioning process on the
other side.