Spatial variability of soil fertility parameters in agricultural lands using geostatistical techniques

Abstract:

If soil fertility were uniform across a farm, every patch would need the same fertilizer dose—but it isn't, and treating it as though it were wastes money and pollutes groundwater. This research mapped the spatial variability of six soil fertility parameters—pH, electrical conductivity (EC), organic carbon (OC), available nitrogen (N), available phosphorus (P), and exchangeable potassium (K)—across 480 hectares of agricultural land in the Warangal district of Telangana using geostatistical techniques. A total of 150 geo-referenced soil samples (0-20 cm depth) were collected on a 200 m grid from irrigated paddy-cotton rotation fields during rabi 2022-23 at Professor Jayashankar Telangana Agricultural University, Hyderabad. Semivariogram analysis fitted spherical models for OC (range: 680 m, nugget:sill ratio 0.32), available N (range: 740 m, ratio 0.28), and available P (range: 520 m, ratio 0.41). Ordinary kriging produced interpolated maps that revealed distinct fertility zones: 34.2 percent of the area was low in OC (<0.50%), 41.7 percent was medium in available N (240-280 kg ha⁻¹), and 52.3 percent was high in exchangeable K (>280 kg ha⁻¹). The nugget:sill ratios indicated moderate spatial dependence for most parameters, driven by management practices rather than inherent soil variation. These fertility maps enable site-specific nutrient management that could reduce blanket fertilizer application by 18 to 24 percent while maintaining crop yield targets.