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.

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Site-specific (precision) management (SSM) has potential for application in managing nematodes and soil conditions in environmentally meaningful ways. Successful application of SSM, however, may be dependent on how agronomically, biologically, and ecologically integrated the plan in question is. Otherwise, SSM risks falling into the ''Tried but did not last'' category. With this background and in addition to describing the concepts and principles of SSM, this presentation discusses the following interrelated points: (1) Case studies of spatio-temporal analysis of soybean cyst nematode (Heterodera glycines) infestations, soil conditions and crop yield in managed ecosystems. Among the critical factors to an accurate and sustained application of SSM are understanding (i) the temporal structure and (ii) the spatial structure of the attribute in question, and (iii) establishing cause-and-effect relationships in the prevailing conditions. New approaches to temporal structure analysis when balancing the purpose of SSM application and nematode biology (as it relates to life stages), population density in soil and root tissue (to determine threshold), and damage functions (physiological stress of the plant during the growing season) are outlined. (2) Application of the concept of fertiliser use efficiency (FUE) to identify soil conditions when managing soil fertility. Defined as increase in host productivity and/or decrease in plant-parasitic nematode population density in response to a given fertiliser treatment, the FUE model recognizes variable responses and identifies four categories of interactions necessary for integrated management decision-making options that account for agronomic, economic, ecological and environmental and pest management issues. (3) Approaches to changing soil conditions in agro-biologically integrated ways. By incorporating nematode community structure (an excellent indicator of soil bio-ecological changes), soil nutrient amendments and crop yield, we have described a modification of the FUE model to identify and monitor changes in soil conditions, thereby creating the necessary bridges to disciplinary and cross-disciplinary gaps and interactions.

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The only well-characterized gene controlling soybean aphid (SBA) resistance is Mi-1.2, a tomato gene that also confers resistance to root-knot nematodes (RKN). Based on similarities between Mi-1.2 and Rag1, which produces a strong antibiosis-type resistance, the authors hypothesized that Rag1 could also provide resistance to nematodes. They evaluated two soybean lines, one carrying the Rag1 gene, and one with no resistance gene, for susceptibility or resistance to soybean cyst nematode (SCN) and RKN. Accepted for publication 4 March 2009. Published 1 April 2009.