Polyacrylamide, sediments, and interrupted flow effects on rill erosion and intake rate

The reduction in the intake rate (IR) during interrupted irrigation is diff icult to predict. Sediments in irrigation water decrease the effect of inte rrupted irrigation on IR. Polyacrylamide (PAM) reduces rill erosion, but it s effect on IR is controversial. The effects of water quality (tap water, t ap water containing sediments, and 10 g m(-3) PAM solution) and interrupted now on IR and rill erosion in an Alfisol (Calcic Haploxeralf) and a Vertis ol (Typic Chromoxerert) were studied using laboratory miniflumes. Pill eros ion in both soils was eliminated by the PAM treatment in both continuous an d interrupted flow. The PAM application reduced IR in the Alfisol and incre ased it in the Vertisol. In the Alfisol, interrupted now reduced IR of the PAM solution by 37% compared with only 18% for tap water. In the Vertisol, interrupted now reduced IR only slightly and the decrease was not affected by the polymer. When the water contained sediments, cumulative infiltration was reduced by 22% for the Vertisol and 59% for the Alfisol in comparison with tap water. These reductions were attributed to depositional seal forma tion. The IR of the Alfisol was more susceptible to depositional seal forma tion than the Vertisol. The presence of sediments in water was effective in reducing rill erosion. The effects of interrupted flow with PAM on reducin g IR were explained by partial blocking of the conducting pores leading to greater suction and compaction of the soil surface. For sediment-laden irri gation water, interrupted flow had no advantage over continuous now in redu cing IR because of depositional seal formation associated with the sediment s in the water.