*4.1. Energy Input and Type of Energy*

The study of energy input is important in rice and wheat at the individual crop level as well as system level due to significant variations in cultivation practices which include CEMs, nutrient management and soil hydrological regimes across a region. The faster adoption of CEMs such as ZTW [41], which is reported to reduce the energy expenditure on tillage, promotion of consortia-based microbial inoculations for nutrient endowments in crops [42,43], thereby reducing the total nutrient applied and increasing the use of micronutrients due to crop response [44,45], was evaluated for biological parameters and economic scale, while their evaluation in terms of energy requirement carries significant importance considering their share in total energy consumption in the crop production process (Figure 1).

In our study, CEMs, rate of N and P application, Zn fertilization and microbial inoculation significantly affected the energetics of RWCS. The higher energy requirement in rice than wheat was contributed by the field preparation, nursery and higher number of irrigations [5,17]. The variation in energy inputs across CEMs in rice was governed by nursery, puddling, seed and sowing and number of irrigations, while in wheat tillage, seed rate and weeding operation contributed to the variation in energy input, with highest contribution coming from tillage. The highest share of fertilization to total energy consumption [18,46] was due to the energy equivalent for N (60.6 MJ kg−1), P2O5 (11.1 MJ kg−1) and K2O (6.7 MJ kg−1) and the higher quantity (90–120 kg N, 44.67–59.1 kg P2O5 and 60 kg K2O) applied, while higher energy equivalents for tractor-operated machinery and diesel increased the share of field preparation in total energy input. As the share of fertilizer in energy consumption is higher in wheat, the increase in energy efficiency by using microbial consortia will be more profitable for wheat. The variation in energy requirement due to irrigation was contributed by rice alone as the irrigation requirement of all CEMs in wheat remained the same. The saving in energy by changing CEM from PTR to ARS was 563.7 MJ ha−<sup>1</sup> (2%). At the same time, this contribution was less if calculated based on monetary terms at the farmer field level which might be due to the subsidized rate of electricity and very low irrigation charges. At the system level, the share of irrigation in total energy input remained the same (6%) even though the difference in energy consumption in irrigation among CEMs is 326.6 MJ ha<sup>−</sup>1. The reduction in energy requirement by changing CEM was reported by [17,47].

The ARS and ZTW were found to be better as they use higher renewable energy than PTR and CDW. The use of higher seed rate and absence of puddling and tillage in ARS and ZTW were the important reasons for higher renewable energy consumption. At the same time, total energy input was also lower in ARS and ZTW which makes them energy-efficient. Both methods were also recommended on the issue of water shortage [48,49] and timely planting along with energy efficiency [7]. Among nutrient management treatments, the use of microbial inoculations reduces the share of non-renewable energy; therefore, treatment with 75% RDN + MC1 or MC2 increases the share of renewable energy in crop production.

The variation in gross energy production arose due to yield superiority of PTR [50] and SRI [51] over ARS in rice and ZTW [52] over CDW and SWI in wheat. The higher gross energy than ARS and lower energy input than PTR make SRI significantly superior in net energy production. The variation across CEMs in energy input and net energy production [53,54] was also reported. We found that in rice and wheat, the variations in energy input and gross energy production contribute equally towards the variation in net energy production among CEMs, while at the system level, the variation in input has the highest contribution to the increase in net energy production.
