Número de amostra para a estimativa da densidade populacional de fitonematoides na cultura de soja (Glycine max (L.) Merrill) e dinâmica populacional em plantas de cobertura

Abstract

Soybean (Glycine max (L.) Merrill) is a crop of great economic importance. Despite numerous advances, soybean cultivation is significantly affected by diseases and pests that cause reduced productivity in different Brazilian regions, especially fungi and nematodes. The sampling of nematodes has become increasingly important in modern agriculture, because through the information obtained from the surveys, an attempt is made to develop sampling plans that are representative, accurate and easy to carry out, and that help in the development of management programs. Among the management strategies, the cultivation of cover plants in the off-season has been an option in reducing the population density of nematodes in the soil. The objective of the work is to collect information on the population dynamics of phytonematodes in commercial soybean farming, determining the number of samples needed to quantify soil nematodes and to assessing the population variation of those micro-organisms in different cover plants. It will be demarcated a grid of 144 sampling points, spaced 10 x 10 m, represented in 1 hectare, in the month of September 2019 to March 2020, in the evaluation before the sowing and R7-R8 stage of the soybean crop. The samples will be collected with the aid of a cutting blade, at a depth of 0-20 cm. The extraction of nematodes in the soil will be performed by the flotation-centrifugation method in sucrose solution, using 100 cm³ of the soil. The extraction of nematodes in the roots will be performed by the blender technique, sieving and centrifugation in sucrose solution. In the suspension obtained, the number of nematodes (1 mL) under an optical microscope shall be estimated using a Peters slide. For sample number analysis, the data were submitted to resampling technique, and a total of 2000 resampling with replacement was calculated. After obtaining the data, it is concluded that nematodes have aggregate distribution and their population density interferes in the amount of samples to be collected. Considering the set of soil and root samples, at the R7-R8 stage, 58 sampling points are necessary to estimate the population density of nematodes, for an estimation error of 65% of the mean and with 95% confidence. Regarding cover plants, they present some divergences as to their effect in relation to nematodes, being able to be promising in relation to the management and to increase or decrease the population density of the species present in the area. The forage turnip, white oats and black oats presented themselves as multiplying plants of the species Helicotylenchus dihystera. For Meloidogyne javanica, the forage turnip crop increased population density, followed by black oats and white oats. For Pratylenchus brachyurus, both black oats and white oats and nabo forage kept the population denside between 20 and 40 specimens/100 cm³ of soil.