Continuous application of phosphatic fertilizers in association with its low recovery results in the insoluble legacy P buildup in agricultural soils. In this study, a field experiment was conducted with maize hybrid COH(M) 6 to know the effect of different P activators (Farmyard Manure, Humic acid, Phosphorus Solubilising Bacteria, and Phytase) on increasing the legacy phosphorus (P) availability. The P activators were combined and applied along with the different doses of P fertilizer (100%, 75%, and 50% soil test dose of P fertilizer). The results showed that the application of Farmyard manure (FYM) and Humic acid (HA) significantly (p < 0.05) increased the soil available P (18.54 kg ha-1) and notably reduced the calcium P fraction (93.08 mg kg-1). The application of FYM and HA with 100% soil test dose of P showed a similar grain (9.98 kg ha-1) and stover P uptake (12.67 kg ha-1) response as that of FYM and HA with 75% soil test dose of P. The study suggested that FYM and HA application has activated the fixed calcium phosphorus in soil and increased its availability for crop utilization. The findings have illustrated that even the reduced dose of P fertilizer application can support the nutrient uptake if they are applied along with P- activators such as FYM and HA. This could promote soil health by reducing the P overload and further P loss in soil.

Sulphur and micronutrients play a vital in the growth and development of plants due to their catalytic effect on many metabolic processes. A field experiment was conducted to explore the changes in various biochemical constituents and antioxidants enzyme activities in response to coated multi-nutrient fertilization. The experiment consisted of five organic acids (citric acid, humic acid, fulvic acid, salicylic acid) and amino acid (glycine) coated multi-nutrient fertilizer sources applied at five different levels (0, 5, 10, 12.5 and 15 kg ha-1). Groundnut leaf samples were collected and analyzed for biochemical constituents such as proline, soluble protein and antioxidant enzymes viz., superoxide dismutase, catalase, peroxidase and carbonic anhydrase activities at harvest stages. The results revealed that, application of fulvic acid coated multi-nutrient fertilizer at 15 kg ha-1 registered lesser proline (5.93 µmoles g-1) and higher soluble protein (22.2 mg g-1) content, superoxide dismutase (8.93 EU mg-1), catalase (18.2 µg H2O2 min-1 g˗1), peroxidase (6.11 µg min-1 mg˗1) and carbonic anhydrase (14.8 EU mg-1) activities at harvest stage followed by 12.5 kg humic acid coated multi-nutrient fertilizer. The lesser response was noted with NPK control in influencing the biochemical constituents and antioxidant enzymes. It was concluded that fulvic coated multi-nutrient fertilizer at 15 kg ha-1 was the better source for improving the biochemical constituents and antioxidant enzymes of groundnut in calcareous soils.