Productivity and nutrient budgeting of rice-wheat cropping systems: Insights from 25 years of long-term fertilization in a Vertisol of subtropical India

The present study aimed to evaluate the nutrient budget, apparent nutrient balance and quantify nutrient depletion and build-up resulting from 25 years of long term fertilization in a Vertisol of Subtropical India. The 150 % NPK recorded maximum positive apparent nitrogen (N) (3038 kg ha-1) and phosphorus (P) (1182 kg ha-1) balance, while minimum was recorded with absolute control (-1604 kg ha-1). The inclusion of green manure (GM) with 50 % NPK registered positive apparent N balance. The apparent P balance was positive with inclusion of P in fertilizer scheduling even under 50 % NPK and 50 % NPK + Blue green algae (BGA) treatments, indicating that 50 % P application fulfilled the crop P demand. The negative apparent K balance was recorded across almost all treatments with the average rate of -181 kg ha-1 yr-1 indicating luxury consumption of K by crops than its supplementation. The soil available N was depleted in all the treatments, however, depletion was minimum under 150 % NPK (10 kg ha-1) and 100 % NPK+FYM (13 kg ha-1). There was build-up of soil available P over initial status in all the imposed treatments (from 5 to 18 kg ha-1) even under sub-optimal dose of NPK, except in absolute control and 100 % N. However, a net negative soil available K was observed in almost all the treatments due to mining of soil K reserves to meet out crop demand. The findings underscore the critical necessity for strategic N and K fertilization in Vertisol under rice-wheat cropping system to sustain optimal nutrient equilibrium, managing soil fertility and maximize agronomic productivity.