ROTATIONAL COVER CROPS IN SANDY SOILS: EFFECT ON ROOT-KNOT NEMATODE POPULATION DENSITIES AND SOYBEAN YIELD

Abstract

Soybean cultivation has increased in the sandy soils of Brazil but improvements in yields have not been realized due to soil degradation and plant-parasitic nematodes. The objective of this study was to analyze the effects of crop rotation on the population dynamics of Meloidogyne incognita and soybean yield. Additionally, the host reaction of sorghum cv. AGRI 002E to M. incognita and M. javanica was evaluated under greenhouse conditions. The field study was conducted in São Pedro do Turvo, SP, in a sandy soil with high M. incognita population densities. Treatments were soybean-maize and soybean-sorghum in rotation with the biological fertilizers Microgeo and Supergan and one additional treatment of Crotalaria spectabilis-maize rotation. Soil and root samples were collected prior to planting and 60 days after establishment of treatments to quantify nematodes. The productivity of soybean was estimated, and costs were quantified. In the greenhouse, sorghum plants were inoculated with 1,000 eggs of M. incognita and M. javanica and, after 60 days, nematodes were extracted to obtain the reproduction factor (RF = final density/initial density). Results showed that higher productivity, as well as a significant reduction in nematode population densities was observed in the plots where C. spectabilis was cropped. With the replacement of soybean by C. spectabilis, the reduction in M. incognita population densities was greater, which allowed for an increase in yield. The biological fertilizers Supergan and Microgeo did not increase soybean yields and did not reduce M. incognita population densities when used once. Sorghum AGRI 002E was susceptible to M. incognita and M. javanica with RF values of 15.1 and 9.5, respectively, and cultivation of this crop must be avoided in areas infested with root-knot nematodes.