*4.2. Energy Production*

Among the nutrient management options, gross and net energy output was affected significantly by the rate of N and P application, Zn fertilization and microbial inoculation. The rate of N and P application had the highest contribution to variation in energy production, while Zn fertilization had the lowest contribution to energy production. The highest gross energy in RDN + Zn was the outcome of highest yield, while the highest net energy production in 75% RDN + Zn + MC1 or MC2 was due to reduction in cost of cultivation on 25% of N and P fertilizer. The difference in energy input across CEMs had a higher contribution to the variation in net energy production than gross energy production. The variation in energy input across CEM was 6.53 <sup>×</sup> 103 to 15.47 <sup>×</sup> 103 MJ ha−<sup>1</sup> for rice, 3.95 to 12.19 MJ ha−<sup>1</sup> for wheat and 10.49 to 27.66 MJ ha−<sup>1</sup> for RWCS, while variation in gross energy production was 125.0–157.1, 125.7–153.1 and 250.9–309.2 MJ ha−<sup>1</sup> for rice, wheat and RWCS, respectively.

The nutrient application through chemical fertilizers is the single most important source of nutrients. Its importance has increased over the years due to increasing nutrient deficiency [55,56], response to fertilization and use of high-yielding nutrient responsive varieties. In terms of energy, fertilizer contributes 59–64% to total energy input in RWCS and the cost of chemical fertilizer is also going to increase in future on account of the increasing cost of fertilizer production, depletion in natural reserves and increasing demand. The rice and wheat together contribute 61% (17.67 million tonnes) to total fertilizer consumption in India. Considering this, complimentary options such as use of microbial inoculations with partial replacement of chemical fertilizers will help in making the RWCS more energy-efficient.
