Alternatives for handling rice (Oryza sativa L.) straw to favor its decomposition in direct sowing systems and their incidence on soil compaction

Abstract

Over 85% of the worldwide area planted with rice is irrigated, mainly by flooding, because this method increases yields. Irrigation by flooding provides this crop with particular characteristics, including at harvest, when it causes difficulties for machinery traffic due to the high soil water content. In addition to this, a large amount of green material is left on the soil, which if not burned, a practice which is prohibited or in the process thereof in many countries, impedes later work to the point where over 600 to 800kg/ha affects establishment of rice in the following season. The above is complicated by the use of direct sowing (DS), which achieves positive results, both in lowering costs and recovering soil, although there is no knowledge of how the planosol soils in Corrientes Province, Argentina, behave under these traffic conditions. The main objectives of this study were to: a) Find out how tools can be used best for improving decomposition of residue from harvesting rice grown under DS and their impact on soil compaction, and b) determine, for short periods, the amount of rice straws deposited on the surface and its decomposition time with various management techniques. A split plot with main factor arranged in a randomized complete block design with four replicates was performed. The use of harvester without spreader, harvester with rubber-flailed spreader, and harvester with metal-flailed spreader was assessed as the main factor. Additionally, three decomposition methods of rice straw were studied as split factor: passing a roller crimper over rice straw, control weed of rice straw with stubble chopper, and burning rice straw. The main results were: a) The harvester without spreader deposited more material in the center of the tail (21.680kg/ha) decreasing toward the sides, and b) distribution done by the harvester with metal-flailed spreader was somewhat similar to the harvester with rubber-flailed spreader but with slightly less uniform deposits. The main conclusions were: 1) When planosol soil was trafficked with loads of 152.5kN, the cone index increased in the subsoil, affecting next growing season, 2) management alternatives that left residue cover attenuated soil compaction caused by the harvester traffic, and 3) the use of a stubble chopper or roller crimper on the rice straw distributed by the harvesters with rubber-flailed or metal-flailed spreaders produced acceleration in decomposition.