Bi-cropping of castor bean and nutri-millets optimizes system productivity, energy efficiency, and carbon footprint in rainfed alfisols of semi-arid tropics

Intercropping enhances diversity, productivity, resilience, and soil health. To achieve these benefits of the intercropping system, drilling patterns and species mixture play a key role. Therefore, to optimize the productivity, profitability, energetics, and carbon footprint of the castor-based millet intercropping system, a field experiment was conducted for two consecutive kharif seasons (2020 - 2021 and 2021 - 2022) at the University of Agricultural Sciences, Bangalore, Karnataka (India). The results revealed that all the crops under monoculture outperformed their intercropping system for seed and stalk/stover yield. Among the different cropping systems, castor + finger millet (2:4) showed highest castor equivalent yield (CEY; 1911 kg ha-1) due to excellent land utilization efficiency (LUE; 106%), land equivalent ratio (LER; 1.13), land equivalent co-efficient (LEC; 0.32) compared to other cropping systems. Castor + finger millet (2:4) was even found superior in terms of monetary returns. Finger millet monoculture showed the highest energy consumption (10,770 MJ ha-1), energy output (96,507 MJ ha-1), and also net energy gain (85,737 MJ ha-1) compared to other cropping systems. However, it was comparable with castor + finger millet (2:4) despite its modest energy consumption (10,530 MJ ha-1). Castor monoculture showed the highest carbon (C) emission (2045 kg CO2-eq. ha-1) and also C output (1760 kg CE ha-1). While, net C gain (1210 kg CE ha-1), C efficiency (3.39 kg kg-1 CE), and C stability index (2.39) were highest in the castor + finger millet intercropping system. Consequently, the adoption of a castor + finger millet (2:4) intercropping system will be a viable alternative for achieving enhanced system productivity, and energy efficiency with lower C-footprints under semi-arid regions.