CONTROLLING SOIL EROSION AND RUNOFF WITH POLYACRYLAMIDE AND PHOSPHOGYPSUM ON SUBTROPICAL SOIL

Abstract

Sandy soil, prone to intense soil erosion, is used for agriculture in the subtropics of Brazil. This study was conductedto determine whether soil amendments are effective for conserving topsoil by preventing water-induced erosion ona Brazilian sandy Alfisol soil (coarse-loamy, mixed, thermic Typic Paleudalf). A programmable rainfall simulator was usedat the experimental station of the Federal University of Santa Maria, in a newly harvested black oat (Avena estrigosa L.) fieldthat was moldboard plowed and disked twice. Plots were on bare tilled soil with 8% to 12% slopes. The soil treatmentsconsisted of a single 5 Mg ha-1 surface application of byproduct phosphogypsum (PG), a single 20 kg ha-1 surface applicationof 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 collectedat intervals during the experiment, and soil surface samples inside the plot were taken after the rain for surface crustinganalysis. Total soil loss was significantly lower for the treatments than for the control and averaged 197, 278, 217, and 2181 kgha-1, respectively for PG, PAM, PAM+PG, and control treatments. PAM and PAM+PG had steady-state runoff ratessignificantly less than that of the control. All of the amendments reduced soil sediment erosion (average 90% reduction) morethan final runoff (average 35% reduction). Using amendments to reduce precipitation-induced erosion is a possiblealternative conservation practice in this region of the world.