Cover crop residue quality regulates litter decomposition dynamics and soil carbon mineralization kinetics in semi-arid cropping systems

Abstract

Cover crop residue addition provides several soil health benefits and serves as a precursor for storing soil organic carbon (SOC). However, information on residue decomposition dynamics and its contribution to soil carbon (C) and nitrogen (N) cycling in arid and semi-arid environments is limited. This study evaluated cover crop residue decomposition in field conditions and C mineralization kinetics in laboratory conditions. For the field experiment, approximately 20 g of Austrian winter pea (Pisum sativum subsp. arvense L.), turnip (Brassica rapa subsp. rapa L.), and triticale (×Triticosecale Wittmack) cover crop residues were kept in litter bags and placed on the soil surface before subsequent forage sorghum (Sorghum bicolor L. Moench) planting in ongoing cover crops study plots. Litter bags were collected every other week (12 destructive samplings) to evaluate the remaining dry matter and C and N contents. The decomposition data were plotted with first order kinetics and exponential models to describe the model fit. To study C mineralization kinetics, a 10-week incubation was set up in a laboratory with Austrian winter pea, turnip, and triticale cover crops and native grass, wheat, and sorghum residues. Carbon mineralization rates were evaluated with three statistical models (first order kinetics and single and double exponential). The exponential model best described the cover crop residue decomposition kinetics in the field. After 98 days, the residue decomposition was higher with Austrian winter pea (47 %), followed by turnip and triticale with ∼40 % biomass decomposition. Residue types and quality both affected the decomposition rates. The C mineralization rate correlated with initial N content (r = 0.87, P < 0.05), C: N ratio (r = −0.88, P < 0.05), and lignin: N (r = −0.87, P < 0.05). While the single exponential model explained field decomposition dynamics, the double exponential decay model best fitted the observed C mineralization trend among the three models. The decay models from our study can be applied to estimate the decomposition dynamics of other winter cover crop residues in similar agroecosystems. This study demonstrated that selecting suitable cover crops and mixtures is critical for maximizing soil C sequestration and N availability in subsequent crops in cover crop-integrated semi-arid cropping systems.