Soil fertility and soil quality index assessment in sugarcane-growing soils of Vellore District, Tamil Nadu

Soil fertility status with special reference to micronutrients and Sulphur in sugarcane-growing areas was assessed by analyzing 308 geo-referenced soil samples collected from 20 blocks of Vellore district, Tamil Nadu. Soil quality assessment of these samples revealed significant spatial variability in major soil properties and micronutrients. The results revealed that soil pH ranged from 6.35 to 8.65, electrical conductivity (EC) from 0.11 to 0.80 dS m^-1, organic carbon from 0.19 to 0.79 per cent. Soils were predominantly (96 percent) neutral to moderately alkaline with non-saline conditions and low (76 percent) to medium organic carbon. Free CaCO₃ content from 0.13 to 12.5 per cent. Nearly 100 per cent were non-saline in nature and 88.6 per cent were non-calcareous. Calcium carbonate and sulphur showed extreme heterogeneity. With respect to micronutrient availability, iron and copper were generally sufficient and the percentage of samples falling under the deficient category for DTPA-extractable Zn and Mn and hot water-soluble boron were 16, 12 and 38 per cent, respectively. Among which available zinc exhibited strong spatial variability with widespread deficiency-prone zones. Available boron showed moderate non-normal distributions. Highly variable CaCO₃, available sulphur, Zn and Cu were key factors controlling soil quality index variation. The computed Soil Quality Index (SQI) value of 0.45 for sugarcane-growing soils indicated that the soils of the study area are of medium quality. The study demonstrates that SQI serves as a reliable indicator for assessing soil suitability for sugarcane cultivation and provides a cost-effective and time-saving approach for soil quality evaluation. The results underscore the need for site-specific nutrient management to enhance soil fertility and agricultural sustainability.