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Reducing tillage intensity and retaining residues are important components of conservation agriculture but in small holder systems in developing countries where crop residues have alternate uses such as fodder and fuelwood, recycling or external additions of organic matter may be a possible option. Information on impacts of long term reduced tillage on soil carbon, labile organic carbon fractions and their depth distribution is scant in drylands of semi arid regions. The effect of tillage intensity (CT—conventional tillage; RT—reduced tillage and MT—minimum tillage) and sources of nitrogen (100% OS: 100% of recommended N through organic source; 50% OS +50%IOS: 50% N through organic source and 50% N through inorganic source and 100% IOS: 100% N through inorganic source) on crop yields, soil organic carbon and C fractions in an Alfisol was assessed at the end of a 10 year long term experiment. Finger millet yields decreased significantly with reduction in tillage intensity (29%). Among N sources, highest yields were recorded with substitution of 50% of the N through organic source. After 10 years, the soil organic carbon (SOC) in 0–20 cm soil layer with MT was 11% higher than with CT. The labile fractions of carbon, viz. particulate organic carbon (POC), microbial biomass carbon (MBC) and permanganate oxidizable carbon (KMnO 4 -C) under MT were 47%, 16% and 43% higher, respectively, in comparison to CT in the 0–20 cm soil layer. The total carbon (TC) and total organic carbon (TOC) with MT were higher by 28% and 27% over CT and higher by 20% and 20% with 100%OS over 100% IOS. Labile carbon fractions revealed differential sensitivity and POC, MBC and KMnO 4 -C are sensitive indicators to detect short term management effects. Reducing tillage intensity and applying various N sources enhanced SOC marginally and the C sequestration rate varied from 62 to 186 kg ha −1 yr −1 . Based on the study it can be recommended for substitution of 50% of the recommended N with organic source as it increases crop yields and soil carbon and could be a potential alternative for residue retention for crops which have fodder value. Reducing the tillage intensity can enhance the SOC in semi arid rainfed systems but lower crop yields under MT is a concern which needs to be addressed in order to make these systems acceptable to the farming community. [ABSTRACT FROM AUTHOR]

Abstract: A long-term experiment was conducted with the objective of selecting the appropriate land management treatments and to identify the key indicators of soil quality for dryland semi-arid tropical Alfisols. The experiment was conducted using a strip split–split plot design on an Alfisol (Typic Haplustalf) in southern India under sorghum (Sorghum vulgare (L))-castor (Ricinus communis (L)) bean rotation. The strip constituted two tillage treatments: conventional tillage (CT) and minimum tillage (MT); main plots were three residues treatments: sorghum stover (SS), gliricidia loppings (GL), ‘no’ residue (NR) and sub plots were four nitrogen levels: 0 (N0), 30 (N30), 60 (N60), and 90kgha−1 (N90). Soil samples were collected after the sixth and seventh year of experimentation and were analyzed for physical, chemical and biological parameters. Sustainable yield index (SYI) based on long-term yield data and soil quality index (SQI) using principal component analysis (PCA) and linear scoring functions were calculated. Application of gliricidia loppings proved superior to sorghum stover and no residue treatments in maintaining higher SQI values. Further, increasing N levels also helped in maintaining higher SQI. Among the 24 treatments, the SQI ranged from 0.90 to 1.27. The highest SQI was obtained in CTGLN90 (1.27) followed by CTGLN60 (1.19) and MTSSN90 (1.18), while the lowest was under MTNRN30 (0.90) followed by MTNRN0 (0.94), indicating relatively less aggradative effects. The application of 90kgNha−1 under minimum tillage even without applying any residue (MTNRN90) proved quite effective in maintaining soil quality index as high as 1.10. The key indicators, which contributed considerably towards SQI, were available N, K, S, microbial biomass carbon (MBC) and hydraulic conductivity (HC). On average, the order of relative contribution of these indicators towards SQI was: available N (32%), MBC (31%), available K (17%), HC (16%), and S (4%). Among the various treatments, CTGLN90 not only had the highest SQI, but also the most promising from the viewpoint of sustainability, maintaining higher average yield levels under sorghum–castor rotation. From the view point of SYI, CT approach remained superior to MT. To maintain the yield as well as soil quality in Alfisols, primary tillage along with organic residue and nitrogen application are needed. [Copyright &y& Elsevier]

Highlights: [•] Climate change is predicted to decrease sorghum yield at sites in India and Mali. [•] Longer crop maturity duration increased the yield of sorghum under climate change. [•] Enhanced yield potential traits increased the yield at all the sites. [•] Drought and heat tolerance traits in sorghum increased the yield at most sites. [•] CERES-sorghum model was useful in quantifying the benefits of traits at the sites. [Copyright &y& Elsevier]