Center Pivot Sprinkler Irrigation Infiltration, Runoff and Erosion Control with Polyacrylamide

Abstract

Polyacrylamide (PAM) applied to furrow irrigated fields at rates of about 1 kg per hectare has been reported to enhance infiltration and control irrigation-induced erosion (Santos and Serralheiro, 2000). Under furrow irrigation PAM dissolved in the furrow stream contacts the soil surface and stabilizes soil structure against shear-induced detachment by enhancing particle cohesion, thereby preventing transport in runoff. Based on the success of PAM with furrow irrigation, many irrigators are interested in using PAM with sprinkler irrigation. Differently from furrow irrigation, water drop impact energy and splash break down soil aggregates and crust soil surface, leading to surface sealing of sprinkled soil surface, and the subsequent runoff and erosion-induced sediment loss. We applied i) 1 kg PAM per hectare to two Fluvisols prior to irrigation and ii) 1 kg ha -1 PAM in the pumped irrigation water to a Luvisol, to identify the effectiveness of PAM in controlling infiltration, runoff and soil erosion of these soils when irrigated with a center pivot system. Field results indicate that significant, and long lasting, infiltration enhancement and runoff and erosion control can be achieved in all studied soils with a single application of 1 kg PAM ha -1 . In the silty-loam Fluvisol PAM treatment reduced erosion approximately 64 and 76% in fallow and crop growing plots, and enhanced infiltration in 34 and 18%, respectively, when compared to control. In the sandy-loam Fluvisol the results, when compared to control, were more dramatic with PAM application reducing soil erosion 98 and 96% in the fallow and crop growing plots and enhancing infiltration in 47 and 45 %, respectively. Concerning the Luvisol, PAM treatment reduced erosion in 46% and enhanced infiltration in 15% in the fallow plots, when compared to control. No significant differences were observed between fallow and crop growing treatments. The field results with PAM applied to Luvisols were significant but less conspicuous than with Fluvisols, due probably to their lesser amount of silt and clay in the soil surface, which not lead to considerable erosion, crusting and surface soil sealing to induce runoff and prevent soil infiltration. Preliminary laboratory tests used to scrutiny PAM effects on soil aggregate stability and infiltration enhancement were important but not sufficiently consistent in all cases to lead to predictions of PAM sediment loss and infiltration control when applied to the fields through center pivot main line.