Sampling optimization for root lesion nematodes in the irrigated wheat fields of Marvdasht region, Fars, Iran

Abstract

The sample size or the number of small fields to be sampled for root lesion nematodes was estimated using CV as a measure of reliability and Taylor’s power law model as a descriptor of nematode spatial distribution in the irrigated wheat fields of Marvdasht region, in autumn 2006. Fifty-six fields were sampled following eight different sampling patterns including: 1-2, sampling the first and the second diagonal transects (D1 and D2 transects, respectively), 3-4, sampling in a line along/across cultivation rows in the middle of field (D3/D4 transects), 5, taking a composite sample from D1 to D4 (Mixed transect), 6-8, the average of D1 to D4 transects (D1-4), D1 and D2 transects (D1-2) and D3 and D4 transects (D3-4), respectively. The number of samples for estimation of population densities of root lesion nematodes with 85% reliability (the most reasonable reliability level for management decisions) were greatest for D3 and D4 patterns (73 and 72 fields, respectively) and smallest for D1-4 pattern (15 fields). According to reliability and cost analysis, the optimum sampling pattern for root lesion nematodes was proved to be sampling on D1-2 transect (cores on two diagonal transects of fields). The data did not fit a negative binomial distribution, which is considered the best probability distribution for description of aggregated count data. The more robust Taylor power law was employed alternatively to verify the spatial pattern of the nematodes and estimate the optimum sample size using its estimated parameters (“a” and “b”). The approach used in the present study can be considered for sampling optimizations of root lesion or other nematodes in wheat or other row crops of regions with soils that are disturbed by heavy cultivation.