Soil fertility and nutrients mediate soil carbon dynamics following residue incorporation

Abstract

A substantial proportion of soil carbon (C) is commonly lost following cultivation of soil and in the transition of pastures to crops. Incorporation of plant residues with nutrient addition (nitrogen, phosphorus and sulphur) may reduce these losses. We investigated the impact of initial soil fertility and supplementary nutrient addition on breakdown of sugarcane residue and associated changes in soil C following a pasture to crop transition. The legume-based pasture was previously managed with fertilizer to develop soils with high and low C. The soils were cultivated with sugarcane mulch (10 Mg ha−1), a C4 crop residue that enabled isotopic 13C tracking, with or without nutrients and sown to a triticale crop [Triticale (× Triticosecale)]. Higher soil fertility with additional nutrients reduced the decrease in total soil C as a proportion of the initial C (14.9% compared to 21.8% without nutrients) to 100 mm depth. Supplementary nutrient addition also resulted in lower physical recovery of sugarcane mulch after 105 days (38.2% in high fertility with nutrients, compared to 97% recovery in low fertility no-nutrient). A larger decline of 13C from the total soil in the high fertility nutrient treatment was similarly observed, compared to low fertility without nutrients (decreases of 47 and 38 mg 13C kg−1 soil, respectively). More fertile pastures with tactical nutrient addition was an effective means for reducing the loss of C during transition to crop.