Submitted to: Managing Irrigation Induced Erosion and Infiltration with Polyacrylamide Co
Publication Type: Proceedings
Publication Acceptance Date: May 6, 1996
Publication Date: N/A
Interpretive Summary: The impact of raindrops or sprinkler drops on bare soil surfaces can cause soil aggregates, clusters of sand, silt, and clay bound by organic or inorganic constituents, to break apart and form a clay skin or seal on the soil surface. This seal, when it subsequently dries, becomes a crust on the soil surface that frequently hinders the emergence of seedlings, particularly sugarbeet. Polyacrylamide or PAM, an environmentally benign, long-chain, synthetic organic polymer with a slight negative charge, if sprayed on the soil surface, may strengthen soil aggregates so that they won't fracture easily. In a field experiment, we sprayed two economic rates of PAM on a soil with relatively weak aggregates and later irrigated the soil with a lateral- move irrigation system, modified to spray drops at a low and high droplet energy. Twenty-four days after planting, we counted the seedlings that had emerged. The PAM rates we studied did not increase sugarbeet emergence at either droplet energy. PAM, in some situations very effective as a soil stabilizer, did not prevent crust development either as we applied it, or where treated surfaces were struck by sprinkler drops. Reducing droplet energy by two-thirds, however, did increase beet emergence by 13%. Such an emergence increase in a nine- county area in southcentral ID would increase sugarbeet producers net income by more than $7M. Our results indicate that producers could increase emergence by reducing the droplet energy striking the soil surface after planting.
Technical Abstract: Drop impact and wetting can cause soil aggregates to slake and form a depositional seal or crust. The seal reduces infiltration which, in turn, increases runoff and soil erosion. Polyacrylamide (PAM) stabilizes surface soil under furrow irrigation and may also reduce aggregate slaking. Less aggregate breakdown would minimize crusting and increase sugarbeet (Beta vulgaris L.) emergence. We evaluated the effects of a moderate charge-density, anionic PAM and sprinkler droplet energy on sugarbeet emergence in the field. In 404 L/ha of solution, rates of 10 and 25 kg PAM/ha of treated surface were sprayed in 25-mm- wide bands onto newly planted rows in a Portneuf silt loam (Durixerollic Calciorthid) near Kimberly, ID, on 25 July 1995. A lateral-move irrigation system, delivering water to the soil surface at two droplet energies, 5 and 15 J/kg, irrigated the plots five times. The PAM applications we used did not increase sugarbeet emergence at either droplet energy. When averaged across droplet energies, emergence in tap water-treated and control(not treated) plots was 10% greater than in PAM-treated plots. PAM's effectiveness as a soil stabilizer is apparently reduced either as we applied it or where treated surfaces are subjected to droplet energy. When averaged across PAM treatments, a three-fold reduction in droplet energy increased emergence more than 13%, significant at P = 0.055. Such an emergence increase in a nine- county area in southcentral ID would increase sugarbeet producers' net income by more than $7M. Our results indicate that producers could increase emergence by reducing the droplet energy striking the soil surface after planting.