CONTROLLING SOIL EROSION AND RUNOFF WITH POLYACRYLAMIDE AND PHOSPHOGYPSUM ON SUBTROPICAL SOIL
Sandy soil, prone to intense soil erosion, is used for agriculture in the subtropics of Brazil. This study was con- ducted to determine whether soil amendments are effective for conserving topsoil by preventing water−induced erosion on a Brazilian sandy Alfisol soil (coarse−loamy, mixed, thermic Typic Paleudalf). A programmable rainfall simulator was used at the experimental station of the Federal University of Santa Maria, in a newly harvested black oat (Avena estrigosa L.) field that was moldboard plowed and disked twice. Plots were on bare tilled soil with 8% to 12% slopes. The soil treatments consisted of a single 5 Mg ha−1 surface application of byproduct phosphogypsum (PG), a single 20 kg ha−1 surface application of anionic polyacrylamide (PAM), a combined amendment (PAM+PG) with the same rates as above, and an unamended soil (control). Simulated rainfall average intensity was 25 mm h−1 with a 2 h duration. Sediment and runoff samples were collected at intervals during the experiment, and soil surface samples inside the plot were taken after the rain for surface crusting analysis. Total soil loss was significantly lower for the treatments than for the control and averaged 197, 278, 217, and 2181 kg ha−1, respectively for PG, PAM, PAM+PG, and control treatments. PAM and PAM+PG had steady−state runoff rates significantly less than that of the control. All of the amendments reduced soil sediment erosion (average 90% reduction) more than final runoff (average 35% reduction). Using amendments to reduce precipitation−induced erosion is a possible alternative conservation practice in this region of the world.