DETERMINING THE EFFECTS OF SOIL CONDITIONERS
ON WATER EROSION IN SOILS WITH DIFFERENT
TEXTURES BY USING RAINFALL SIMULATOR
Mucahit Karaoglu1,*, Ferdi Acar21Igdir University, Agricultural Faculty, Soil Science and Plant Nutrition Deparment, Igdir, Turkey 2Agricultural engineer, Turkey
ABSTRACT
The water erosion, which can be observed in every region where high intensity precipitation and sloping lands are present, is a type of erosion that erodes the soils at most. In this study, simulated rainfalls having the intensity of 100 (± 3) mm.h-1 were applied for one hour on three different eroded soil samples (Clay loam, Sandy loam and Loam) through three different methods involving Control, PAM (7.5 kg.ha-1) and PG (7.5 ton.ha-1) in three repetitions. While PAM applications increased final infiltration values at the rate of 70% and total infiltration values at the rate of 39-48%, they decreased runoff values at the rate of 19-41%, runoff erosion at the rate of 200-300% and amount of soil replaced with side splash at the rate of 250-300%. PG applications increased final infiltration values at the rate of 54-57% and total infiltration values at the rate of 28-38% whereas they decreased runoff values at the rate of 20%, runoff erosion at the rate of 190-260% and amount of soil replaced with side splash at the rate of 200-260%. PAM applications enhanced more positive effect of 0-50% for all erosion processes. According to results of analysis of variance, positive effects of PAM and PG on erosion processes were found to be significant at P<0.05 and P<0.01.
KEYWORDS:
Rainfall simulator, PAM, PG, infiltration, runoff, erosion
INTRODUCTION
Accelerated water erosion can be reduced since it is human-induced and amounts of soil loss can be decreased to the tolerance limits. Soil protection activities are not only limited with correct cultural operations, but also benefit from the positive contributions of soil conditioners. Most common of these are polyacrylamide (PAM) hy-drophilic, and high molecular and polyvinyl alcohol (PVA). Some research has been conducted with these polymers, and different results have been
yielded [1]. In previous studies, it was reported that the effects of PG and PAM applications were per-manent whereas effects of surface covering and tillage were temporary [2].
Impact energy of raindrops may lead to the formation of seal on the soil surface. This causes serious problems in agricultural areas in arid and semi-arid regions. The application of PG on soil surface leads to stability in the amount of electrolytes [3], ensures the release of electrolytes in water entering soil and transferring to runoff, acts as mulch, prevents subsidence of soil particles on the surface [4], keeps electrolyte level at a high level, reduces the formation of seal by ensuring aggregation of clays, increases infiltration, decreases the amount of sediment washed away from surface [5], and restricts the soil loss increasing with the increase of slope [6].
The effects of consecutive (7-day interval) simulated rainfall (intensity of 45 mm.h-1 and 1-hour), slope (2, 6, 15, 24 and 30%) and PG (0, 5 t.ha-1, 10 t.ha-1) on runoff and erosion were investi-gated on two soil samples (clayey and silty loam), and positive effects of PG were observed on all results as statistically significant (P<0.01) [7]. A similar study was conducted so as to determine the effects of consecutive simulated rainfall, slope and PG on seal formation and infiltration rates, and thinner seal occurred and the increase in infiltration rates were found as statistically significant (P<0.01) in PG treatments [8].
PAM application increases cohesion strength between soil particles, can meliorate soil micro structure and aggregate stability against water [9, 10, 11, 12], maintains soil structure, enhances re-sistance of soil to erosion, reduces soil erosion susceptibility factor (K), increases infiltration, de-creases amount of runoff [13, 14, 15] and as a result it reduces seal formation and soil loss [16, 17, 18, 19, 20].
In laboratory conditions, at parcels with slope of 20%, PAM was sprayed on soil texture of clay (Typic Hapludult) in rates of 0, 20, 80 and 120 kg.ha-1 and simulated rainfalls (70 mm.h-1) were applied 1, 2, 8, 30 and 60 days after. As a result of this research, PAM dozes of 80 and 120 kg.ha-1 significantly decreased the runoff and the amount
of sediment. It is reported that seal layer on soil surface was hard in the waiting period after PAM applications. As a result, when runoff amounts increased, soil losses decreased [21].
In another study, PAM was applied to two soil samples (clay and sandy) with irrigation water as 10 mg.L-1 in order to determine the effect of PAM on infiltration capacity, water holding capacity, and aggregate stability. The differences of Control-PAM were found statistically significant (P<0.01) for initial infiltration rate, indifferent for final infil-tration rate, significant (P<0.05) for aggregate sta-bility, and indifferent for water holding capacity [22].
PVA and PAM were sprayed as solution at the density of 1000 mg.L-1 (667 gr. da-1) and 100 mg.L-1 (66.7 gr.da-1) on three sandy-loamy textured soil samples and after 24 hours, simulated rainfalls were applied at a density of 65 mm.h-1 and 1-hour period to parcels. As a result of this study, polymers applications were found more effective on the soil sample with higher aggregate stability, and it was determined that this effect changed according to the type and dose of polymer, and that PVA signifi-cantly reduced the amount of runoff and soil loss [23].
In an investigation, PAM and PVA were sprayed as 6.70 and 33.50 kg.ha-1 on soil samples (sandy clayey loam and sandy loam), and simulated rainfalls were applied at the density of 65 mm.ha-1 for 1-hour period. The decrease in runoff and the resistance of seal layer due to polymer applications for soil samples of sandy loam [24] was found statistically significant (P<0.05).
Gel of hydrophilic PAM was sprayed as 0.2% w/w on soil surface with sandy clayey loam texture and high amount of calcareous. After the soil sur-face dried, hydrophobic of polyvinyl acetate (PVAc) was sprayed as 0.5 and 1.0% w/w. Accord-ing to the results of this study, it was determined that polymers reduced seal formation at a signifi-cant level [25].
PAM (20 kg.ha-1) and polysaccharide (PS) (40 kg.ha-1) were applied on vertisols with silty loam and clay texture, and parcels were subjected to simulated rainfall with the intensity of 100 mm.h-1. In this study, the runoff was found 39-53% of the rainfall; PAM and PS applications reduced runoff and soil loss at significant level, however, seal formation increased the runoff amount [26].
According to results of another study, where different rates of PAM and PS were sprayed on soil samples (Typic Chromomert and Typic Haploxe-ralf), and simulated rainfall of 60 mm.h-1 intensity was applied for five times, it was observed that PAM increased permeability and decreased the soil loss [27].
In a study, where silty loam soils (Calcic Hap-loxeralf) in containers with 120 mm diameter and 78 mm height were subjected to spray PAM and
PS, and simulated rainfall of 40 mm.h-1 intensity was applied. The containers were placed in a drying cabinet at 40°C. Resistances of seal occurring on soil surface were measured with hand penetrometer. It was determined that the resistances of seal at the parcels where PS and PAM were sprayed were lower than control parcels [28].
The effects of PAM and PG on tillage (surface tillage breaks seal layer) and the effects of surface cover on runoff and soil loss were investigated on soils having sandy loam texture (clayey Typic Kanhapludult) in natural rainfall conditions. As a result, PG and PAM applications reduced runoff and soil loss 67 and 44%; and 16 and 19% accord-ing to control treatments, respectively. The positive effects of PAM and PG on decreasing runoff were higher than those decreasing of soil loss [2].
In different research, PAM+PG mixtures and simulated rainfalls of 3 mm drop diameter from different heights (0.4, 1.0 and 1.6 m) were applied on soils (Typical Chromoxerert, Typical Rhodox-eralf and Calcic HaploxRhodox-eralf). It was reported that the infiltration rates reduced and soil loss amount increased when the height of rainfall increased. In addition, PAM+PG applications increased infiltra-tion rates and decreased the amount of soil loss compared to control and PG parcels [29].
In this study, the effects of PG and PAM on infiltration, runoff and erosion under high intensity rainfall (100 mm.h-1) generated by rainfall simulator and critical slope (6%); the difference between them; and the statistical significance of this difference were investigated on three different soil samples that were susceptible to erosion.
MATERIALS AND METHODS
3 soil samples used in this study were eroded soils which were taken from (0-20 cm) sloping lands (6%) in the Tuzluca district of Igdir province, located in Eastern Turkey. Air-dried soil samples were sieved from a 2-mm sieve for physical and chemical analyses. Soil texture [30], organic matter [31], hydraulic conductivity [32], aggregate stability [33] and soil structure (manual exami-nation) were determined. Soil samples used in experimets of rainfall simulation were sieved from a 8-mm sieve [24, 23].
Tuzluca district which has a continental climate, is an arid region. The average annual precipitation is 273.0 mm. According to the long term meteorological data, although it has the lowest precipitation amount of Turkey, there are 25 thunderstormy or rain showery days there [34].
PAM used in this research has a relative densi-ty of 0.750 gr.cm-3 and molecular weight of 16 Mg.mol-1. When molecular weight of PAM increas-es, the length of the polymer chain and viscosity of the PAM solution increase [35]. PAM with high
molecular weight is more effective in clay aggrega-tion, and its effect on infiltration is more than PAM with low molecular weight [36, 35]. The second soil conditioner PG is waste matter of fertilizer factories used phosphorite, and has 97% CaSO4, 1% MgSO4, 0.6% P2O5, 1.4% fluorapatit and SiO2 in dry composition of it [7, 8].
A laboratory-type rainfall simulator generated a 0.5 cm drop diameter [37], the metal pans had the dimensions of 50x22 cm while the splash plates used to measure the sediment amount carried via side splashes had a height of 1.5 m, and tap water for simulated rainfall [24] with the pH value of 7.29 and an electrical conductivity of 27.3 mS.m-1 were used in this study.
100±3 mm precipitation was applied during 81 one-hour rainfall processes. Coarse filter paper and 3-cm deep soil samples onto of it were placed in pans, and a slope of 6% was given to the pans. Soil samples were subjected to rainfall simulation in air-dried condition without being saturated. 1-hour rainfall period was started for each sample when infiltration started.
82.5 gr PG (7.5 ton.ha-1) was mixed in the upper 1-cm layer of the soil samples in the pans. 82.5 mg PAM (7.5 kg ha-1) on infiltration, runoff, splashing and the amount of soil lost by runoff at the slope of 6%; PAM was dissolved in 1 liter of distilled water [38, 39, 24] at the temperature of 65°C for 25 minutes and was sprayed on the soil samples in pans [24, 23] and after the soil samples were kept for 1 hour [47].
After the soil sample reached saturation, the infiltration was measured 6 times with 10-minute interval. Infiltration values in soil continue decreasing during precipitation and remain stable after reaching a certain value [4, 6, 3, 8]. This value is called as final infiltration and generally soil conditioners contribute to the increasing of total and final infiltration values.
Splash plates were placed 6 cm away from pans placed in the rainfall simulator [41, 7]. Soil particles collected from plates were washed with a washing bottle in every 15 minutes, and were taken to the containers placed in the discharge outlet of the collecting canal with an approximate slope of 15% in the lower parts of plates. The collected material was assessed as the amount of soil that splashed sideways and replaced.
In order to determine the amount of washed sediment and runoff that may occur in pans with
slope of 6%, collection containers were placed on the outlet of slopped apron at the tips of pans when rills were formed. A glass cover was placed on the apron in order to prevent the raindrops falling on pans’ apron from mixing into runoff [41, 7]. Runoff measurements were conducted with 15-minute interval.
The jars collecting runoff and sediments were kept for sedimentation for a while and when the runoff water became clear, amount of runoff water was measured through siphoning. However, since a certain amount of runoff water left with sediment, measuring containers were weighed right after the siphoning process and kept on 60˚C hot-plate for drying. After the drying process, they were weighed again and the difference between wet and dry sediment amounts was added to the runoff amount [41, 7].
Analysis of variance was conducted in order to determine whether or not the differences between final infiltration, total infiltration, runoff, side splash, and the amount of soil lost by runoff measured in control, PAM and PG soil samples used in the study were significant, or in other words to determine whether or not PAM and PG had any positive effect or not.
RESULTS
Table 1 shows the results of physical analysis applied to soil samples. According to the results of the texture analysis, the soils had clay loam, sandy loam, and loam soil textures. Since aggregate stability values also increased with increasing amount of organic matter in soils [42]. Aggregate stability values of soil samples with low organic matter amounts (0.5-1%) were also measured as low (40-55%). Hydraulic conductivity values varied between 60-66 mm h-1. According to these values, soil samples had moderate permeability. Soils with high hydraulic conductivity had low susceptibility to water erosion [43]. Soil structure determination was performed visually and all three soil samples were found to be very thin granular. Soil erosion susceptibility factor (K) values were respectively 0.24, 0.28, and 0.33 for the soil samples. Accordingly, all soil samples were involved in the class of substantially erodible soils.
TABLE 1
Results of physical analysis
Soils Sand % Silt % Clay % A.S. % O.M. % H.C. (mm h-1) C.C. S.S. K
CL 37.2 25.6 37.2 53.76 0.73 62.1 3 1 0,24
SL 66.8 18.0 15.2 40.95 1.07 65.7 3 1 0,28
L 52.7 28.5 18.8 43.71 0.59 63.9 3 1 0,33
CL: Clay Loam; SL: Sany Loam; L: Loam; Aggregate stability; O.M: Organic matter; H.C: Hydraulic conductivity; C.C: Conductivity class; S.S: Soil structure;
TABLE 2
Infiltration values (mm.m-2.h-1)
Clay Loam 1 2 3 4 5 6 Total
C 10.0 8.6 8.0 6.0 4.7 4.5 41.8
PAM 14.0 12.6 10.1 9.3 7.8 7.8 61.6
PG 13.4 11.9 9.9 8.6 7.0 7.0 57.8
Sandy Loam 1 2 3 4 5 6 Total
C 11.2 9.6 8.5 6.8 5.2 4.8 46.1 PAM 14.7 13.1 10.8 9.1 8.1 8.1 63.9 PG 13.7 12.4 9.9 8.8 7.4 7.4 59.6 Loam 1 2 3 4 5 6 Total C 10.5 9.0 8.2 7.3 5.1 4.4 44.5 PAM 14.0 12.6 11.2 9.6 7.5 7.5 62.4 PG 13.7 11.9 10.2 8.0 6.9 6.9 57.6
C: Control, PAM: Polyacrylamide, PG: Phosphogypsum. Table 2 illustrates Control, PAM and PG
infiltration values of soil samples used in the study. Total infiltration values of control trials were lower than hydraulic conductivity values given in Table 1 for every soil sample. Its most significant cause was that aggregates degraded due to the erosive effect of raindrops and small soil particles filled the holes on the surface to create a seal [6].
Applications of PAM increased final infiltration and total infiltration values. The increases in total infiltration values were 1.5 times for the sample 1, 1.4 times for the sample 2, and 1.4 times for the sample 3. The increase in the final infiltration values was 1.7 for all three soil samples. In other words, compared to control trials, the positive effect of PAM application was 39-48% greater for total infiltration values and 70% greater for final infiltration values. Applications of PG also increased final infiltration and total infiltration values. The increases in total infiltration values were 1.4 times for the sample 1, 1.3 times for the sample 2, and 1.3 times for the sample 3. The increases in the final infiltration values were 1.6 times for the sample 1, 1.5 times for the sample 2, and 1.6 times for the sample 3. In other words, compared to control trials, the positive effect of PG application was 28-38% greater for total infiltration values and 54-57% greater for final infiltration values. The rate of positive effect between PAM and PG for all three soil samples and total and final infiltration values was 1.1 times or PAM was 10% more effective.
Rills were observed due to the impact effect of raindrops in the control trials [45] and the kinetic energy of raindrops (KE) dispersed soil aggregates as separate particles. Clays led to seal formation [6] and increase of runoff by clogging pores, which exist in the surface and beneath the surface. Low-amount PAM applications carried out under simulated rainfalls performed with high-density tap water were observed to reduce runoff compared to control values [40].
Table 3 shows control, PAM and PG-applied runoff values of soil samples as mm.m-2.h-1. Applications of PAM decreased runoff values [13,
14, 15]. This decrease was 1.4 times for the sample 1, 1.2 times for the sample 2, and 1.3 times for the sample 3. In other words, the effect of PAM application reducing runoff was 19-41% for runoff values compared to control trials. PG applications also decreased runoff values in the study [4, 6, 3, 7]. This decrease was 1.2 times or 20% for all three soil samples. The rate of positive effect between PAM and PG for three soil samples and runoff amounts were 1.2, 1.0, 1.1 times respectively or PAM was 20-0-10% more effective.
TABLE 3 Runoff amounts (mm.m-2.h-1) CL 1 2 3 4 Total C 0.4 1.1 5.3 7.9 14.7 PAM 0.2 0.6 2.7 6.9 10.4 PG 0.2 0.6 4.3 7.2 12.3 SL 1 2 3 4 Total C 0.3 1.0 4.7 7.8 13.8 PAM 0.1 0.8 3.6 7.1 11.6 PG 0.1 1.0 3.9 7.0 12.0 L 1 2 3 4 Total C 0.2 0.9 5.0 7.9 14.0 PAM 0.1 0.5 3.9 6.3 10.8 PG 0.1 0.5 4.2 6.9 11.7 PG [4, 6, 3], PAM [15, 46, 47, 48, 49] and PG+PAM [50] made a decreasing effect on physi-cal disintegration of aggregates caused by kinetic energy of raindrop. As PG increases the electrolyte concentrations in runoff and leaking water, aggregate distribution is prevented and bigger aggregates are carried away in smaller quantities. Thus, erosion caused by runoff is reduced [2]. PG also decreases the sediment concentration in runoff volume [51]. Amount of sediment removed by runoff depends on aggregat stability against raindrop impact [52], and as aggregate sizes in-crease, their transportation via runoff are difficult [53, 54, 6].
Table 4 shows amounts of soils that were carried away with runoff or were exposed to water erosion and replaced by side splash as g.m-2. Positive effects of PAM and PG were seen also in
soil loss. Control values of runoff erosion decreased 3.3 times for the sample 1, 2.8 times for the sample 2 and 2.3 times for the sample 3 in PAM application, or PAM application decreased the erosion caused by runoff at the rate of 200-300%; the values decreased 2.6 times for the sample 1, 2.2 times for the sample 2 and 1.9 times for the sample 3 in PG application, or PG application decreased the erosion caused by runoff at the rate of 190-260%. PAM decreased the amounts of soils replaced by side splash 2.9 times for the sample 1, 2.5 times for the sample 2 and 3.0 times for the
sample 3 or at the rate of 250-300%; whereas, PG decreased the amounts of soils replaced by side splash 22.6 times for the sample 1, 2.0 times for the sample 2 and 2.0 times for the sample 3 or at the rate of 200-260%. The rate of positive effect between PAM and PG for three soil samples and total erosion were 1.3, 1.3, 1.2 times respectively or PAM was 30-30-20% more effective. The rate of positive effect between PAM and PG for three soil samples and total side splash were 1.1, 1.3, 1.5 times respectively or PAM was 10-30-50% more effective.
TABLE 4
Erosion and side splash (g.m-2)
Trials Erosion Side splash
CL 1 2 3 4 Total 1 2 Total
C 19.11 50.05 269.36 691.60 1030,12 1840.33 1928.41 3768,74 PAM 9.10 20.02 90.30 223.02 313,32 690.42 626.62 1317,04 PG 12.20 21.56 128.80 238.21 400,77 770.45 665.05 1435,50
Erosion Side splash
SL 1 2 3 4 Total 1 2 Total
C 20.99 58.51 270.40 782.19 1132,09 2065.21 2246.46 4311,67 PAM 12.00 24.22 99.75 266.25 402,22 831.01 910.90 1741,91 PG 13.85 33.24 128.80 328.98 504,87 1060.44 1120.19 2180,63
Erosion Side splash
L 1 2 3 4 Total 1 2 Total C 23.11 72.05 303.40 801.10 1199,66 2330.96 2480.08 4811,04 PAM 15.10 30.92 102.37 366.25 514,64 786.40 816.19 1602,59 PG 17.20 43.62 178.58 382.09 621,49 1155.90 1240.80 2396,70 TABLE 5 Variance analysis. Dependent Variables Statistic Variance sources
Soils Soil conditioners
CL SL L C PAM PG Final Infiltration N 3 3 3 3 3 3 Mean 6,43 6,76 6,26 4,56 7,80 7,10 S. Error 0,038 0,038 0,038 0,038 0,038 0,038 LSD b** a** c** c a** b** Total Infiltration N 3 3 3 3 3 3 Mean 53,73 56,53 54,83 44,13 62,63 58,33 S. Error 0,47 0,47 0,47 0,47 0,47 0,47
LSD a** b** ab** c a** b**
Runoff N 3 3 3 3 3 3 Mean 12.46 12.46 12.46 14,16 10,93 10,93 S. Error 0,31 0,31 0,31 0,31 0,31 0,31 LSD - - - a b** b** Erosion N 3 3 3 3 3 3 Mean 581,40 679,72 778,59 1120,62 410,06 509,04 S. Error 9,05 9,05 9,05 9,05 9,05 9,05 LSD c** b** a** a c** b** Splash Erosion N 3 3 3 3 3 3 Mean 2173,76 2744,74 2936,78 4297,15 1553,85 2004,28 S. Error 129,37 129,37 129,37 129,37 129,37 129,37 LSD c* b* a* a c** b** *P<0.05; **P<0.01
Table 5 illustrates variance analysis results of total and final infiltration, runoff, erosion and side splash values obtained under 6% slope and rainfall simulation with 100 mm.h-1 intensity performed with different soil conditioners and different soil samples used in the study. Effects of soil samples and soil conditioners on final infiltration values were significant (P<0.01); effects of soil samples on total infiltration values were significant at the level of P<0.05; effects of soil conditioners were significant at the level of P<0.01; effects of soil samples on runoff values were insignificant, effects of soil conditioners were significant at the level of P<0.01; effects of soil samples and soil conditioners on erosion values were significant (P<0.01); effects of soil samples on side splash were significant at the level of P<0.05 and the effects of soil conditioners were significant at the level of P<0.01.
DISCUSSION
A well-developed and verified laboratory-type rainfall simulator gives reliable results and provides important savings in term of money and time. However, rainfall simulators used in the studies are not in a certain standard and therefore, different results can be obtained in the studies.
Soil conditioners, which are among the protection precautions taken to pull down accelerated erosion to tolerance values, should be cost-effective and easy to obtain. High expenses in the agricultural sector can prevent soil loss via water erosion which is hidden danger.
Although PAM showed a better protection effect than PG in this study, it is not yet produced in Turkey and it is expensive since it is imported. In this case, usage of PG comes into prominence in the control of water erosion for Turkey. However, the costs of shipping and labor in application phase should also be taken into account for PG.
CONCLUSION
In countries such as Turkey where a great majority of agricultural lands have critical and high slopes (≥6%), water erosion is a serious problem. The main well-known protection method against water erosion is to cultivate the soil correctly and not to leave it bare. However, fallowing and stubble burning are still serious problems in Turkey.
Doubtlessly, commonly known cheapest ideal method is the continuity of the vegetation cover. Since last two decades, residue cover and no-tillage have been primary applications in soil conservation. Soil loss except for natural erosion has the highest cost for humanity because its recovery is impossible in the short term.
ACKNOWLEDGEMENTS
We are grateful for the financial support from the Unit of Scientific Research Projects (2013-FBE-L11) of Igdir University-Igdir, Turkey.
The authors have declared no conflict of interest.
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Tarım Topraklarında Yapay Yağmurlayıcı Yardımıyla Taşlar, Bitki Artıkları ve Polyvinil Alkol’ün (PVA) Toprak Özellikleri ile Birlikte Erozyona etkileri Üzerinde Araştırmalar. E.Ü.Z.F. Yayın No: 474.
Received: 01.05.2017 Accepted: 26.05.2018 CORRESPONDING AUTHOR Mucahit Karaoglu Igdir University, Agricultural Faculty,
Soil Science and Plant Nutrition Department, Igdir – Turkey
