Soil Sampling Spacing Based on Precision Agriculture Variable Rate Fertilization of Pomegranate Orchard

Variable rate fertilization is one of the core technologies of precision agriculture, and it is particularly important to develop a representative field sampling scheme with less workload. A grid sampling of 1 m × 1 m was conducted on a pomegranate garden of 414 m2 in Nanzhuang Town, Jianshui County, Honghe Hani and Yi Autonomous Prefecture, Yunnan Province, and set up 7 groups of sample point deletion schemes to study the reasonable sampling spacing of soil nutrients. Based on the grading standard of soil nutrients in plow layer, the distribution of soil nutrients was statistically analyzed by using classical statistical methods to reveal the spatial distribution variability of soil nutrients. We then utilized a geostatistical method to interpolate the soil nutrient to obtain the soil nutrient distribution map, and compared the soil nutrient distribution map of the deletion sampling scheme with the original sampling scheme A in shape and area. Results revealed that the deletion scheme E was the most consistent with the sampling results of the full coverage sampling scheme A, and the number of soil sampling could be reduced by half under the premise of meeting the requirements of precise fertilization. The field experiment showed that the variable rate fertilization could save 26%, 54% and 34% nitrogen, phosphorus and potassium fertilizer compared with the farmers' conventional fertilization, the total yield of soft seed pomegranate increased by 41.52%, and the sugar content, sugar–acid ratio and vitamin C content of pomegranate grain increased by 11.79%, 51.26% and 31.59%. The results also provide support to determine sampling spacing, spatial variability of soil nutrients and variable rate fertilization in precision farming.