Effects of NPK and Micronutrient Fertilization on Soil Enzyme Activities, Microbial Biomass, and Nutrient Availability

The combined effects of macronutrients (Nitrogen, Phosphorus, and Potassium-N, P, K) and micronutrient fertilization on turmeric yield, soil enzymatic activity, microbial biomass, and nutrient dynamics remains poorly understood, despite their significance for sustainable soil fertility management and optimizing crop productivity across diverse agroecosystems. To investigate, a net house experiment on sandy loam Haplic Chernozem was conducted to 03 fertilizer regimes, viz. N₇₅P₅₀K₅₀ kg ha⁻¹ (T-2), N₁₂₅P₁₀₀K₁₀₀ kg ha⁻¹ (T-3), and N₁₀₀P₇₅K₇₅ + B₃Zn₆Fe₆ kg ha⁻¹ (T-4). Furthermore, the influence of these treatments was systematically assessed on soil nutrient status (N, P, K), enzymatic activities (alkaline phosphomonoesterase, dehydrogenase, fluorescein diacetate hydrolysis), microbial biomass carbon (MBC) and soil organic carbon (SOC). Balanced fertilization significantly turmeric productivity and soil health. All three fertilizer treatments showed a clear yield increase compared to the unfertilized control. Compared to the control, N₇₅P₅₀K₅₀ kg/ha T-2 increased rhizome number and biomass per plant by 44.7% and 16.3%, respectively, while N₁₀₀P₇₅K₇₅ + B₃Zn₆Fe₆ kg/ha T-4 further enhanced them by 86.6% and 27.7%. T-3 produced the most significant yield response by increasing the rhizome biomass by 38.0% and rhizome number per plant by 100% compared to the control. The nutrient availability was also substantially improved. T-2 enhanced the soil nitrogen contents by 83.3% with maximum N levels observed in T-3 & T-4. Phosphorus increased by 61.5% in T-3 and 37.3% in T-4, while potassium was enhanced by 12.9% in T-3 relative to the control, respectively. Enzymatic activities were markedly enhanced as T-3 was recorded to improve alkaline phosphomonoesterase (APA), dehydrogenase (DHA) and fluorescein diacetate hydrolysis (FDA) by 50.6%, 37.4%, and 43.4%, where T-4 increased by 32.2%, 30.9%, and 35.9%, respectively compared to control. MBC and SOC also rose significantly, with SOC increased by 13.8% (T-2), 41.6% (T-3), and 47.2% (T-3) relative to control. The result of this study demonstrates that the integrated macro & micronutrient fertilization, particularly T-3 7 T-4 treatments, sustainably enhanced turmeric yield, soil nutrient availability, enzyme activity, microbial biomass, and organic carbon. These findings highlight the critical role of balanced nutrient management in sustaining soil fertility and crop productivity across agroecosystems.