Optimization of citrus tree sampling pattern for estimating population of citrus nematode in the soil of infested orchards in Fars province, southern Iran.

Number of cores per citrus tree (sample size) needed to estimate the citrus nematode count (second-stage juveniles and males) in the soil was investigated. Coefficient of variation of mean (CV) was used as a measure of reliability and Taylor's power law model was used as a descriptor of nematode spatial distribution. The study was replicated twice during early winters 2018 and 2019 in two citrus orchards of Fars province, southern Iran. For each of the six selected trees, 10 cores (10–15 cm in diameter × 30 cm in depth) were systematically sampled from beneath each tree canopy; six and four cores from the outer and inner parts of irrigation dripline, respectively. Second-stage juveniles (J2s) and males of the nematode in soil were extracted using a Bearman tray method for 48 h. Besides 10 single samples from each core, the sampling patterns were designated in two forms of real and virtual compositions. Real compositions included of an average of two or three composite samples from outer and/or inner part of irrigation dripline. The virtual compositions corresponded to the real compositions and were formed by combining nematode count data rather than soil samples. Parameters of Taylor's power law model were estimated by fitting the model to the data and used for sample size calculations for this nematode. The results of the two trials revealed that in terms of reliability, and cost an average of two composite samples from the outer (six cores) and inner (four cores) areas of the irrigation dripline could be recommended as the best sampling plan for estimating the nematode population in infested orchards. • Different sampling patterns for citrus nematode were evaluated to find the best one. • Taylor power law model was used to describe variability of nematode count in soil. • Sample size was optimized using CV of the mean as a measure of precision. • Cost of sampling is the second criteria to choose the best sampling pattern. • To achieve higher reliability, larger sample sizes with higher costs are required. [ABSTRACT FROM AUTHOR]