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Conservation tillage systems are advocated worldwide for sustainable crop production; however, their favorable effects on soil properties are subject to the length of their use. The following study aimed at using the CENTURY agroecosystem model to simulate long-term changes in soil organic carbon (SOC) fractions and wheat (Triticum aestivumL.) production. Tillage systems include conventional tillage (CT, control), minimum tillage, chisel plow (CP) and zero tillage with (R+) and without residues (R−) in fallow-wheat system. The model validation with 2-year field experiment showed that the simulated results were strongly correlated with observed results for total organic carbon (r2 = 0.94), active soil carbon (r2 = 0.91), slow soil carbon (r2 = 0.84) and passive soil carbon (r2 = 0.85). Similarly, model simulations for biomass and grain yields were, respectively, 81% and 76% correlated with observed results. The long-term simulations predicted that SOC stock and its fractions will gradually build up, crop biomass and grain yield will enhance with crop residue retention, especially under chisel plough in comparison of existing CT system. The study concludes that CP and retention of crop residues have potential to improve SOC contents and ultimately crop production. [ABSTRACT FROM AUTHOR]

A 2-year research experiment was laid out in a split-plot design with moldboard ploughing (MP, control) and minimum tillage (MT) as main plots and crop sequences as sub-plots. Summer-winter cropping sequences were fallow-wheat (Triticum aestivumL.) (FW, control), mungbean (Vigna radiataL.)-wheat (MW), sorghum (Sorghum bicolorL.)-wheat (SW), green manure-wheat (GW) and mungbean-chickpea (MC) (Cicer arietinumL.). During 2010–2011, in summer, mungbean crop produced the highest above ground biomass in mungbean-chickpea sequence under MP tillage (4.24 Mg ha–1mungbean) and in mungbean-wheat sequence under MT tillage (4.11 Mg ha–1mungbean). In winter, chickpea gave the highest biomass in mungbean-chickpea sequence under both tillage systems. During 2011–2012, mungbean produced the highest above ground biomass in mungbean-wheat sequence under MT tillage (4.43 Mg ha–1mungbean) and in both the mungbean-chickpea and mungbean-wheat sequences under MP tillage (4.24 and 4.17 Mg ha–1mungbean, respectively). In winter, fallow-wheat sequence gave the highest biomass in both tillage systems. The differences in grain yields were statistically non-significant in both the years. The gross marginal benefit ranged between −190 and 548$ ha–1in the first year and −165 and 1124$ ha–1in the second year. The net benefit values were the highest in mung-chickpea sequence under both tillage systems (1008 and 596$ ha–1under MP and MT, respectively), which gave cost–benefit ratios of 5.45 and 3.68, respectively. Use of legume-based cropping sequences is a sustainable and cost-effective practice in drylands of northern Punjab, Pakistan. [ABSTRACT FROM PUBLISHER]