Spatial and Temporal Interactions of Meloidogyne incognita and Soybean

The spatial and temporal dynamics of Meloidogyne incognita, relative to soybean shoot and root growth in field microplots, were determined at 11 sampling dates during a growing season. The population dynamics of M. incognita on soybean were dependent on initial population (Pi), soil moisture, and root spatial distribution. Final egg and juvenile population densities were greatest in plots with higher Pi. The population densities of juveniles and eggs were highest from mid- to late-season and were associated with increased soil moisture. Root spatial distributions and M. incognita numbers were closely related. Numbers of juveniles and eggs decreased with soil depth and distance from the center of the row. Greater numbers of juveniles and eggs were found in the upper 30 cm in the row center, and in the upper 15 cm at 10 and 20 cm from the center of the row. There were no consistent differences in root weights between nematode-infected and uninfected plants at any depth or distance from the center of the row. The optimum time for determining the relationship between Pi and soybean shoot growth was from late mid-season (September) to final harvest (14 November). The relationship between Pi and seed yield for the final harvest was best described by a quadratic model: yield (g) = 71.4 + 1.1(log[Pi + 1]) - 2.3(log[Pi + 1])(2), (R(2) = 0.99, P = 0.03).