Geostatistical analysis of field spatial distribution patterns of soybean cyst nematode

Site-specific management of soybean cyst nematode [Heterodera glycines Ichinohe] (SCN) is plausible if its spatial and temporal dynamics are adequately known and structured. The hypothesis that variation in the spatial distribution of SCN is sufficient in magnitude and structure and sufficiently time invariant to support the use of site-specific management in SCN-infested fields was tested. A nested survey sampling design with distances reduced by geometric progression was applied on two fields in Michigan. Cysts were extracted from single-core soil samples collected before planting in 1999 and 2000, the number of eggs per cyst was estimated, and the number of eggs per sample was obtained by multiplying eggs per cyst by the number of cysts. The distribution of the three variables was characterized using geostatistical tools such as semivariograms, kriging, and cross-correlograms on log-transformed values of the original data. Mean cyst population density ranged from 6 to 33 cysts 100 cm(-3) soil in the two fields. Although the spatial structure of SCN population varied between fields and SCN population density varied between years, the location of areas of high or low cyst density could be identified repeatedly. The reasons why nematodes exhibited an aggregated distribution are not yet understood. The evaluation of factors associated with the determination of SCN spatial distribution is part of an ongoing project toward the development of SCN site-specific management.