Evaluating the effectiveness of a hydrophobic polymer for conserving waterand reducing weed infection in a sandy loam soil

In this work we tested the influence of different solutions of a hydrophobi c polymer named Guilspare (R), applied to the soil surface to reduce soil e vaporation, on the soil water status, soil temperature, crop performance an d weed emergence. Two tests were carried out on a farm of the Guadalquivir river valley, southwest Spain, one with a maize crop and the other with bar e soil. In the test with maize, we evaluated the effect of applying a solut ion of 2% v/v of Guilspare (R) in water, at the rate of 31 m(-2), on the cr op performance and weed emergence. On both the treated and the untreated co ntrol plots, three rates of irrigation were applied, namely 100, 75 and 50% of the locally determined optimal irrigation depth to cover the crop needs for an optimum development and yield. For the case of 50% of the irrigatio n dose, the performance of the crop treated with the polymer (T50) was much better than that of the untreated control plot (C50). The crop height and green leaf area index for T50 were nearly as good as for the C100 control p lants receiving 100% of the irrigation dose. The T50 crop was 73% of the yi eld of the treated and fully irrigated T100 crop, while the C50 yield was o nly 38% of the C100 yield. The treated crop reached the different phenologi cal stages quicker than the untreated crop. The polymer was effective in re ducing weed emergence. In the test with bare soil, 0.8% v/v of Guilspare (R ) in water, at the rate of I I m-2, kept levels of water content in the soi l as high as other solutions with greater amounts both of polymer and water . The average soil water content during the irrigation period in this lower treatment was 34 and 53% higher at depths of 0.15 and 0.25 m, respectively , than in the untreated plots. No influence of the polymer on soil temperat ure was observed. Results from additional measurements on weed emergence an d hydraulic conductivity of the soil surface showed that the polymer was st ill effective 7 months after application, In fact, the hydraulic conductivi ty in the range near saturation was 44% greater in the treated plots than i n the untreated ones, and the number of weeds was 27% lower. (C) 2001 Elsev ier Science B.V. All rights reserved.