Thursday, January 11, 2007 - 3:45 PM

Geostatistical Analysis of the Spatial Variability of Cotton-parasitic Nematodes and the Factors Favoring Its Occurrence

B. V. Ortiz1, Dana Sullivan2, Calvin Perry3, George Vellidis3, and Robert Kemerait4. (1) Auburn University, Agronomy and Soil Department, 204 Extension Hall, Auburn, AL 36849-5417, (2) TurfScout® LLC, 2316 RAINWATER ROAD, Tifton, GA 31794, (3) University of Georgia - Tifton Campus, Biological & Agricultural Engineering Department, 2329 Rainwater Rd, Tifton, GA 31794, (4) University of Georgia, 160 Plant Science Building, Tifton, GA 31794

Delineation of management zones for a site-specific management of cotton-parasitic nematodes requires the study of their spatial and temporal variability. If field-scale distributions of nematodes spatially correlate with specific biotic or abiotic conditions present in the field, those conditions can be used as surrogate data to identify risk areas of cotton yield reduction due to nematode infection. A systematic sampling design with square grids of 0.20 ha in size was applied on 10 cotton fields in South Georgia in 2005 and 2006. The study involved the analysis of the spatial variability of the southern root knot nematode (Melodogyne incognita) sampled three times during every growing season, distributions and its relationship with soil texture, soil electrical conductivity, elevation, slope, and canopy spectral reflectance from multispectral images collected every month during the growing season. The study of the spatial variability based on geostatistical analyses involved the calculation of semivariograms, identification of the degree of spatial structure, kriging interpolations, and the validation of the kriging estimations using a random selection of a subset of data points from every variable under study. Areas having a high probability of nematode populations greater than established threshold populations will be identified via indicator and disjunctive kriging.

Recorded presentation