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Title: Runoff and interrill erosion in sodic soils treated with dry PAM and phosphogypsum

Author
item TANG, Z - CHINA AGRIC UNIV
item LEI, T - CHINA AGRIC UNIV
item YU, J - CHINA INST OF WATER RES
item SHAINBERG, I - AGRIC RES ORG, ISRAEL
item Iliasson, Amrax
item BEN-HUR, M - AGRIC RES ORG, ISRAEL
item LEVY, G - AGRIC RES ORG, ISRAEL

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/22/2005
Publication Date: 2/27/2006
Citation: Tang, Z., Lei, T., Yu, J., Shainberg, I., Mamedov, A.I., Ben-Hur, M., Levy, G. 2006. Runoff and interrill erosion in sodic soils treated with dry PAM and phosphogypsum. Soil Science Society of America Journal 70:679.690.

Interpretive Summary: It is well known that an increase in soil sodicity in arid and semi-arid zones seriously increases soil vulnerability to sealing, runoff, and erosion. Most studies found that surface application of a soil amendment such as polyacrylamide (PAM) and/or gypsum (PG) was effective in stabilizing soil aggregates, and decreasing seal formation, runoff and erosion. PAM can be directly applied through the irrigation water or by spraying a PAM solution. Neither practice is suitable for rain-fed agriculture because water for spraying the PAM solution is not available and because it is difficult to dissolve PAM in water. For instance to apply 20 kg ha–1 of PAM, the volume of PAM solution to be sprayed is 20 m3 ha–1 because solutions of > 1000 g m–3 are too viscous for practical use. Spreading dry PAM at the soil surface has the advantages of low shipping cost, long shelf life, elimination of the difficult dissolution of dry PAM in irrigation water and elimination of the handling of the viscous PAM solution. We investigated the effects of surface application of dry granular PAM and PG combinations on the infiltration rate (IR), runoff, and wash erosion from semi arid soils under simulated rainstorms. We used four semi-arid smectitic soils varying in texture (loamy sand, loam, sandy clay and clay). Each soil had four sodicity levels (non, low, medium and high, e.g exchangeable sodium percentage from 2 to 20). Increasing soil sodicity increases the intensity of clay dispersion and its importance in the processes of seal formation and erosion. Thus in untreated soils increasing sodicity from non sodic to high sodicity, decreased steady state or final IR more than up to 6 times and increased runoff and wash erosion up to 3 times. Spreading PG alone or PAM mixed with PG on the soil surface significantly increased the final IR (up to 6-15 times) and decreased runoff and soil loss (up to 5 times) compared with the control/untreated samples. The trend of the effects was similar yet it depended on soil texture. Spreading the mixture of dry PAM with PG resulted, in all cases, in higher relative final IR values, over the entire sodicity range studied, compared with those obtained for spreading just PG. When PG is added to the soil surface it dissolves during the rainstorm and releases electrolytes to the soil solution and thus prevents clay dispersion. Application of PAM mixed with PG decreased runoff and soil loss by the same mechanisms identified for PG and also by binding particles at the soil surface by the polymer chains. Cementing the soil particles stabilized them against detachment and increased their deposition rate. Spreading of dry granular PAM mixed with PG could potentially be considered as a management tool for reducing soil susceptibility to crust formation in rainfed agriculture, where physical and physico-chemical destabilization of the surface aggregates are the dominant mechanisms in erosion.

Technical Abstract: Seal formation at the soil surface during rainstorms reduces rain infiltration and leads to runoff and erosion. An increase in soil sodicity increases soil susceptibility to crusting, runoff, and erosion. Surface application of dissolved polyacrylamide (PAM) mixed with gypsum was found to be very effective in decreasing seal formation, runoff, and erosion. The objective of this study was to investigate the effects of surface application of dry granular PAM (20 kg ha21) mixed with phosphogypsum (PG) (2 and 4 Mg ha21) and that of PG alone on the infiltration rate (IR), runoff, and wash erosion from four smectitic soil types (ranging in clay content between 10 and 62% and sodicity level between exchangeable sodium percentage [ESP] 2 and 20) exposed to simulated distilled water rainstorms. Increasing ESP from 5 to 20 in the loamy sand decreased final IR from 14 to 2 mm h21 and increased runoff and wash erosion in the control; similar trends but of different magnitude were noted in the other soil types. Spreading PAM mixed with PG or PG alone was effective in maintaining final IR . 12 mm h21, low runoff, and wash erosion levels compared with their control. Use of PAM mixed with PG resulted in higher final IR and lower runoff levels than PG alone in all four soils studied. Conversely, with respect to soil erosion, PAM mixed with PG was more effective than PG alone in reducing wash erosion from the loamy sand and clay and had comparable effects on soil loss in the loam. It was concluded that for rain-fed agriculture, spreading of dry granular PAM mixed with PG was more effective than PG alone in reducing runoff and erosion in soils varying in texture and sodic conditions.