Spatial variability of extractable potassium in sandy-paddy soils in Northeast of Thailand: study of optimal distance between the sampling points

Abstract

Information on spatial variability of potassium (K) extracted in soil is an important for rice cultivated on sandy soil. To be able to manage the soil correctly, appropriately and precisely, so the distance of sampling points is an important factor. The objective of this study was to describe spatial variability of the concentration of K in sandy soil and to assess the appropriate distance for soil collection using geostatistics. The study was conducted in Phra Yuen District, Khon Kaen Province. There were 5 study areas, included the rice planting area for less than 5 years (N1 and N2) and the planting area for more than 30 years (L1, L2 and L3). Each site, 100 of soil samples were collected according to the stratified systematic unaligned sampling method in 5x5 m grid size in the area of 2,500 m² (50x50 m). The results showed that the variation of K concentrations in both areas were moderate to high, with an average value of 167 ± 57, 201 ± 71, 134 ± 27, 107 ± 38 and 103 ± 40 mg/kg for N1, N2, L1, L2 and L3, respectively. The semivariogram shows that the spatial dependence of K concentrations were high in N1, L1, L2 and L3, while N2 had a moderately level. The results indicated that the optimal distance for soil sampling were 8 - 90 m and 3 - 44 m for the rice planting area for less than 5 years and the planting area over than 30 years, respectively.