How sustainable is organic management in cassava? Evidences from yield, soil quality, energetics and economics in the humid tropics of South India

Abstract Sustainable alternative agricultural practices like organic farming have evinced interests  due to public consciousness about food safety, environmental pollution, soil quality and human health. The study aimed to evaluate the productivity, soil quality, energetic and economic aspects under organic vs conventional management in cassava (Manihot esculenta Crantz). Field experiments were conducted over a three year period at ICAR-Central Tuber Crops Research Institute, Thiruvananthapuram, India in split plot design with three varieties of cassava, H-165, Sree Vijaya and Vellayani Hraswa, in main plots and five production systems, traditional, conventional, integrated and two types of organic (without and with microbial inoculants) in sub plots. Organic management (without microbial inoculants) (27.26 t ha−1) produced insignificant yield increase (+2.40%) over conventional system (26.62 t ha−1). The industrial (H-165) as well as domestic varieties (Sree Vijaya, Vellayani Hraswa) of cassava exhibited similar performance under the different production systems. At the end of the third crop,  soil chemical properties like pH and organic C were significantly enhanced by 1.15 unit and 22.58% under organic (with microbial inoculants) over conventional system, whereas the soil porosity, cation exchange capacity and exchangeable Ca were significantly higher by 9.36, 27.32 and 29.10% in the organic (without microbial inoculants) over conventional. Besides, biological improvement of the soil with higher counts of bacteria, fungi and actinomycetes and greater activity of soil enzymes like acid phosphatase and dehydrogenase were also observed under organic (with microbial inoculants) system. Both the organic practices (without and with microbial inoculants) scored higher soil quality index (SQI) over the rest, but similarly (0.98 and 0.94 respectively). The soil pH, exchangeable Ca, dehydrogenase enzyme activity and porosity were the decisive factors that governed SQI in the present study. Organic system (without microbial inoculants) proved to be the most energy efficient as evidenced from the highest energy output (152.63 × 103MJ ha−1), net energy (143.55 × 103MJ ha−1), energy use efficiency (16.80) and energy productivity (3.00 kg MJ−1). Organic system generated the highest net income (US $ 4977.57 ha−1) statistically similar to conventional (US $ 4833.10 ha−1) and organic with microbial inoculants (US $ 4720.69 ha−1). Hence organic practices can be recommended for sustainable cassava production.