Spatial variability of some soil properties for site specific farming in northern Iran

Evaluating agricultural land management practices requires knowledge of soil spatial variability and understanding their relationships. Spatial distributions for fourteen soil physical and chemical properties were examined in a wheat field in Sorkhankalateh district, in Golestan province, Iran. 101 soil samples at the distances of 5m, 10m and 20m as nested grid were collected at the depth of 0-30cm in early December 2004 just after planting the winter wheat in a plot (1.8 ha area). Data were analyzed both statistically and geostatistically on the basis of the semivariogram. Frequency distribution of all data was normal. The spatial distribution and spatial dependence level varied within location. The range of spatial dependence was found to vary within soil parameters. Nitrate had the shortest range of spatial dependence (23.99m) and K had the longest (93.92m). Eight parameters including pH, EC, sand, silt, clay, P, CaCO3 and organic matter (OM) were moderately spatially dependent whereas saturation percentage (SP), bulk density (Db), K, N, cation exchange capacity (CEC) and exchangeable sodium percentage (ESP) were strongly spatially dependent. The results demonstrate that within the same field, spatial patterns may vary among several soil parameters. Soil nutrients were found to be affected by farmer management. Variography and kriging can be useful tools for designing effective soil sampling strategies and variable rate application of inputs for use in site-specific management.