Abstract
Organic matter management is key to sustain ecosystem services provided by soils. However, it is rarely considered in a holistic view, considering local resources, agro-environmental effects and harmonization with farmers' needs. Organic inputs, like compost and biochar, could represent a sustainable solution to massive current challenges associated to the intensification of agriculture, in particular for tropical regions. Here we assess the potential of agricultural residues as a resource for farmer communities in southwestern India to reduce their dependency on external inputs and sustain ecosystem services. We propose a novel joint evaluation of farmers' aspirations together with agro-environmental effects of organic inputs on soils. Our soil quality evaluation showed that biochar alone or with compost did not improve unilaterally soils in the tropics (Anthroposol, Ferralsol and Vertisol). Many organic inputs led to an initial decrease in water-holding capacities of control soils (-27.3%: coconut shell biochar with compost on Anthroposol). Responses to organic matter inputs for carbon were strongest for Ferralsols (+33.4% with rice husk biochar), and mostly positive for Anthroposols and Vertisols (+12.5% to +13.8% respectively). Soil pH responses were surprisingly negative for Ferralsols and only positive if biochar was applied alone (between -5.6% to +1.9%). For Anthroposols and Vertisols, highest increases were achieved with rice husk biochar + vermicomposts (+7.2% and +5.2% respectively). Our socio-economic evaluation showed that farmers with a stronger economical position showed greater interest towards technology like biochar (factor 1.3 to 1.6 higher for farmers cultivating Anthroposols and/or Vertisols compared to Ferralsols), while poorer farmers more skepticism, which may lead to an increased economical gap within rural communities if technologies are not implemented with long-term guidance. These results advocate for an interdisciplinary evaluation of agricultural technology prior to its implementation as a development tool in the field.
Highlights
Agricultural intensification over the last decades has contributed substantially to the decrease of ecosystem services provided by soils [1, 2]
In case of the Anthroposol, except for coconut shell biochar (B1 = 13.52 ± 0.54; p > 0.05), all organic matter (OM) inputs resulted in significant decreases in water-holding capacity (WHC), up to –27.29 ± 0.97% compared to the control (B2+C1 = 10.12 ± 0.14%; p < 0.05)
Despite low initial value (5.97 ± 0.24%—Table 1; characteristic of soils from the subhumid tropics [51, 67]), the WHC of the Ferralsol only tends to increase with coconut shell biochar alone (B1 = 6.07 ± 0.16%; p > 0.05) or the same biochar mixed with composts (B1+C1 = 6.57 ± 0.07%, B1+VC1 = 6.26 ± 0.31% and B1+VC2 = 6.12 ± 0.02%), but only the first two of the mixed OM inputs were significantly different from the control soil (Table 4; p < 0.05)
Summary
Agricultural intensification over the last decades has contributed substantially to the decrease of ecosystem services provided by soils [1, 2]. In India, the liberalization of agriculture during the green revolution in the 1960ies induced a trend towards cash crop production [5, 6] and contributed to major ecological as well as socio-economic crises [7]. The reduction of soil fertility, and decreasing crop yields, has led to significant farmers’ distress and indebtedness [5, 8], necessitating an urgent, yet possible [9] shift towards sustainable agricultural practices and simultaneous support to ecosystem services essential for food production and farmers livelihoods [10, 11]. The surplus OM (i.e. OM not used for any other domestic purposes) is between 25–72%, including major crops grown in the study area in Karnataka (sugarcane bagasse, wheat, coconut shell, rice straw, banana) [16, 17]
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