Mapping of Macronutrients in Soils of Amritsar District (Punjab) – A GIS Approach

Spatial distribution of nitrogen (N), phosphorus (P), potassium (K) and sulphur (S) was studied at flag leaf stage of wheat (Triticum aestivum L) by collecting random geo-referenced surface (0–0.15 m) soil samples from 645 sites representing different soils using global positioning system (GPS) and mapped on 1:50,000 scale in Amritsar district of north-west Punjab. The plant (flag leaves) samples were also collected simultaneously from every 4^th soil sampling site. These soil samples were analyzed for N, P, K and S and plant samples for P, K and S and categorized as low, medium and high as per criteria followed in the soil testing laboratories. The content of available N varied from 63 to 170 kg ha⁻¹, available P from 9.4 to 84.9 kg ha⁻¹, available K from 84 to 700 kg ha⁻¹ and available S from 24.6 to 60.0 kg ha⁻¹. The contents of total P in plants varied from 0.09 to 0.23%, total K from 0.84 to 3.10% and total S from 0.14 to 0.29%. Soil nutrient maps showing the spatial distribution were prepared in Arc Info GIS. The maps of various nutrient elements clearly indicated the specific locales, where deficiency of nutrients constrained crop production. Multi-nutrient (NPK) map suggested that the combined NPK deficiency at a single place was negligible. Based upon the linear coefficient of correlation between macronutrients and soil properties, a significant positive correlation occurred between organic carbon and N, K and S. The available nutrients showed a negative correlation with CaCO₃.