Monday, November 5, 2007

Mulch and Polyacrylamide Interactions on Steep Slopes.

Deanna Babcock and Richard McLaughlin. Department of Soil Science, North Carolina State University, Raleigh, NC 27695

The application of mulch products to bare soil is frequently used to decrease soil erosion. The addition of polyacrylamide (PAM) has been demonstrated to reduce erosion even further. We conducted tests in a rainfall simulator on two types of hydromulches and straw in combination with PAM (37 kg ha-1) to determine the relative improvements in erosion control achieved by adding the PAM. We also compared applications of dry (granular; 37 kg ha-1 and 74 kg ha-1) and aqueous (37 kg ha-1) PAM with straw. The tests were done on 2 m x 1 m soil boxes tilted to an 18 slope. Both cotton-based and wood fiber mulches decreased turbidity and total suspended solids (TSS) relative to similar rates of straw mulch. Cotton was more effective at reducing rates of erosion compared to wood fiber and straw. Total sediment loss for cotton mulch was on the order of 76 kg ha-1, while both wood fiber and straw were above 200 kg ha-1. Increasing cotton or wood fiber mulch rates from 2000 kg ha-1 to 3000 kg ha-1 tended to improve runoff quality and reduce erosion rates by 18-57%. Additionally, aqueous PAM application, regardless of mulch type, was found to reduce total suspended solids (TSS), turbidity, and erosion rates up to 90% compared to straw alone. Granular PAM application was similarly effective in turbidity reduction regardless of application rate, but the low rate actually increased TSS and total sediment loss relative to straw without PAM. Total sediment loss was reduced only at the higher dry PAM rate. Low rates of granular PAM, though aiding in the formation of soil floccules, may be insufficient at preventing floccule transport, increasing soil loss.