Spatial variability of soil micronutrients in the intensively cultivated Trans-Gangetic Plains of India

• The spatial variability of soil micronutrients in the Trans-Gangetic Plains of India was assessed.
• The nugget/sill ratio values were 0.60, 0.37, 0.34 and 0.19 for available Zn, Fe, Cu, and Mn, respectively.
• Semivariogram range values of Fe, Cu, Zn and Mn were 140, 61, 32 and 5 km, respectively.
• The distribution maps generated could be used as a guide for precise and site-specific micronutrient management in the study region.

Soil micronutrient deficiency adversely affects crop production in intensive agriculture. However, information on the spatial variability of key micronutrients in intensively cultivated regions of India is limited. Thus, the present study was carried out in the Trans-Gangetic Plains (TGP) region of India with the hypothesis that spatial variability of micronutrient availability is high due to small farms and varied management. The major objectives of the study were (i) to assess the spatial variability of plant available micronutrients, viz. extractable zinc (Zn), copper (Cu), manganese (Mn) and iron (Fe) at a regional scale through geostatistical methods, (ii) to develop distribution maps for soil micronutrients using ordinary kriging and (iii) to assess the relationships of micronutrient availability with several soil properties. A total of 5638 soil samples, representative of the surface (0–15 cm) horizon were collected (covering Inceptisols, Entisols, Alfisols and Aridisols) during April to June between 2011 and 2014 from farms in 21 districts of the TGP. For each micronutrient, semivariograms were calculated and their main parameters (nugget effect, sill and range) were obtained. Moderate spatial dependence for extractable Zn, Cu and Fe and strong spatial dependence for extractable Mn were recorded. The nugget/sill ratio values were 0.60, 0.37, 0.34 and 0.19 for extractable Zn, Fe, Cu and Mn, respectively. Available Fe, Zn, Mn and Cu deficiencies (including acute deficiencies) were observed in 28, 15, 14 and 13% of soil samples, respectively. Soil pH showed significant and negative correlations with the concentrations of extractable Zn, Cu, Mn and Fe; whereas the correlation was significant and positive with soil organic carbon (SOC) concentration. The distribution maps generated could be used as a guide for precise and site-specific micronutrient management in the study region.