Assessing soil fertility and spatial variability is essential for site-specific fertilizer recommendations in heterogeneous soils. This study evaluated the fertility status of Bankanahalli micro-watershed, Mandya taluk in the southern dry-zone of Karnataka with an annual rainfall of 633.91 mm and LGP of 120 days. A total of 45 grid-based (320 × 320 m) surface soil samples were analyzed for key fertility parameters. Results showed that available nitrogen, phosphorus and potassium ranged from 119.17 to 567.62, 16.42–84.17 and 24.24–236.88 kg ha − 1 , respectively. Soils were low in organic carbon, slightly to moderately alkaline (pH 6.32–8.64) and non-saline (EC 0.01–0.46 dS m − 1 ). Spatial variability of nutrients was quantified using ordinary kriging in ArcGIS 10.5. Thematic maps were prepared using best-fit semivariogram models with lower RMSE values. The study’s key novelty was recalibrating conventional low, medium, high (L-M-H) fertility ratings to a five-tier system: very low, low, medium, high, and very high (VL-L-M-H-VH), enabling finer nutrient variability capture. Raster maps of fertility variability were reclassified and overlaid to generate combination fertility maps for both systems, followed by site-specific fertilizer recommendations. This classification revealed greater nitrogen and potassium needs, enhancing precision in identifying nutrient-deficient areas and improving nutrient use efficiency and productivity.
Girish et al. (Thu,) studied this question.
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