International Conference on
WATER MANAGEMENT IN ARID AND SEMI-ARID LAND, 2017
19-23 March 2017, Irbid, Jordan.
Control of soil erosion of Agricultural Land in Jordan with polyacrylamide
Majed Abu-Zreig1*
1Professor of Water and Environmental Engineering, Jordan University of Science and Technology
Irbid, Jordan
Email: ;
Abstract
Field experiments were conducted to test the effect of two types of polyacrylamide on soil erosion and runoff of agricultural land in Jordan. A commercially named PAM as A836 and A870, have different molecular weight ranging qualitatively from high to low and surface charge from 20% to 70%, respectively were used. PAMS were applied on field plots with 2 m wide by 10 m long having a slope of 11%. The runoff and sediment loss from each plot was collected for each natural storm using a collection barrel installed at the downstream end of plots. The PAMs were applied at 2 application rates of 10 and 30 kg/ha. Experimental results showed that both types of PAM caused large reduction in soil loss with an average value of 22% compared to control and 70% compared to compacted plots. Application of A836 reduced runoff and sediment loss by 23% and 35%, respectively compared to control. The corresponding average decreases in runoff and soil loss for A870 were lower at 16% and 8%, respectively. Differences in runoff among PAM treated plots at 10 and 30 kg/ha were negligible but soil loss was slightly lower in the 30 kg/ha PAM treated plots.
Keywords: PAM, Field plots, Soil loss
1. Introduction
The decline in rainfall and soil moisture in arid climate causes serious desertification problems to agricultural soil. During the last twenty years, desertification due to decline in rainfall and climate change have received increasing attention globally. Efforts to combat desertification from cropland were first aimed at reducing soil erosion and increasing soil moisture within fields. Means for reducing runoff and soil erosion such as using organic polymers were considered.
Wide varieties of organic polymers have been explored in the past at varying degree of success (Marsh & Groenevelt, 1992). Recent studies showed that small rate of polyacrylamide can improve soil structure and aggregate stability, increase infiltration thus reducing runoff and soil erosion (Flanagan et al., 2002; Peterson et al., 2002; Bjorneberg and Aase, 2000). Polyacrylamide is a water-soluble high molecular weight of synthetic organic polymer that interacts with the clay fraction of soils (Seybold, 1994).
Most of studies involving PAM application have been conducted using laboratory or small field plot under simulated rain. The effectiveness of PAM has been found to vary under those conditions (Flanagan et al., 2002). Recently, Abu-Zreig (2006) found that high molecular weight nonionic PAM with 20 to 30% surface charge had the highest influence on soil erosion. But he also found that low molecular weight PAM with 70% surface charge was also quit effective in reducing runoff and soil loss. There is a need to confirm these results using large field plots under natural rainfall conditions.
2. Materials and Method
Fourteen plots of 2 m by 10 m were constructed in the field, at the campus of Jordan University of Science and Technology at Northern Jordan, and bordered by 200mm high stone border. Barrels of 130 L capacity each were installed at the end of each plot for runoff collection. The prevailed soil type is silt loam with average sand, silt and clay ratios of 20, 45 and 35%, respectively. The bulk density of soil was 1100 kg/m3.
Experimental plots were smoothed with hand tools to create a uniform slope that varied with the original land slope (11%). The experimental design was complete block design in which plots were randomly divided in to 7 groups of two plots each with seven treatment; plastic mulch, compaction, PAM 836 at 10 and 30 Kg/ha, PAM 870 at 10 and 30 kg/ha and control. The PAMs used in the study were obtained from Cytec Company under the name of Superfluc A-836 and superfluc A-870. PAM solutions were prepared at 0.1% concentration and 20 L of a diluted solution was spryed on soil within 24 hours of preparation using hand-held sprayer to obtain the specified application rate.
Runoff volume and sediment concentration were measured in the barrels after each storm for the fourteen plots. Sediment concentrations were measured by method of drying.
3. Results and Discussion
Twenty storms were recorded for the entire season, 2004/2005, with rainfall depth ranging from 2 mm to 35 mm per day and total rainfall depth of 206 mm. Thirteen storms with rainfall depth greater than 5 mm produced runoff whereas no runoff was observed for the other six storms.
3.1 Runoff and Infiltration
Application of PAM significantly decreased runoff at both treatment levels compared to control and compacted plots. Figure 1 shows runoff reduction in PAM treated plots compared to control.
Figure 1. The runoff reduction caused by PAM treatment
The average runoff depth in the control and compacted plots were 53 mm and 72 mm, respectively compared to 45 mm for A870 (13.5% reduction) and 40 mm for A836 (23.5% reduction). However, runoff differences between the 10 and 30 kg/ha application rate were small and insignificant (only 1 mm) and therefore only average values were reported in Table 1.
Further analysis was performed to test the longevity of PAM during the winter season. The relative runoff coefficient of PAM treated plots seemed to remain constant or slightly decreased with time in the case of A870 suggesting PAM persistence along the season.
3.2 Effect of polyacrylamide on soil loss
The influence of PAM on soil loss is summarized in Figure 2 .
Figure 2. Soil loss reduction (%)
Soil loss from PAM treated plots was significantly lower than those in the control plots for each storm for both application rate (P<0.05). The total soil loss from control plots were 2672 kg/ha and decreased by an average of 36% for PAM treated plots. PAM A836 had significantly higher soil loss reduction (48% compared to control) compared to A870 with 25% reduction. PAM A836 concentration had significant effect on soil loss causing a 41% and 54% reduction at 10 and 30 kg/ha, respectively (Figure 2). The corresponding soil loss decrease in the case of A-870 was lower at 25% and 26%. Unlike its influence on runoff PAM seemed to reduce sediment loss at higher degree. These results were in agreement with erosion studies involving PAM application found in literature.
The effectiveness of PAM under simulated rainfall condition seemed to be higher than that under natural rainfall conditions. Flanagan et al. (2002) found that PAM application under simulated rain reduced runoff and sediment yield by 52 and 91%, compared to about 30 and 49%, respectively under natural rainfall. In a previous study, Abu-Zreig (2006) found that application of PAM A836 and A870 at 10kg/ha reduced soil loss by an average of 46% compared to 33% in the present study. This is because soil erosion under natural rainfall is dominated by interill erosion at which PAM is less effective while simulated rain caused more rill erosion at which PAM is more effective (Flanagan, 2002; Peterson et al., 2002). In addition differences in the ionic composition between natural and simulated rainfall may contribute to these differences in soil loss (Smith et al. 1990; Sheinberg et al., 1990).
4. Conclusion
Results obtained from field experiments in the arid land of Jordan showed that application of small rate of polyacryamide (PAM) decreased runoff and soil loss significantly by an average of 19% and 36%, respectively. Application of the high molecular weight PAM A836 resulted in significant runoff and soil loss reduction at 23% and 48%, respectively. The corresponding reductions for the A870 characterized as low molecular weight and high surface charge were 14% and 25%, respectively. The longevity of PAM seemed to continue for the whole year.
References
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