Carbon sequestration and yields with long-term use of inorganic fertilizers and organic manure in a six-crop rotation system

Cultivation practices and nutrients management have a profound influence on soil productivity and the sequestration of soil organic carbon (SOC). However, there have been few integrated studies on yields and SOC dynamics following application of organic amendments in long-term multiple-crop-rotation systems. The aim of this study was to assess the effects of different nutrient management, on yield and SOC sequestration potential through a 33-year field experiment (rice–wheat/broad bean–maize/cotton–barley, each cycle of rotation taking 3 years). The treatments were (1) control, with neither fertilizers nor manure, (2) nitrogen and phosphorus but no potassium (NP), (3) nitrogen, phosphorus, and potassium (NPK), (4) pig manure alone (M), (5) pig manure combined with NP (MNP), and (6) pig manure combined with NPK (MNPK). MNPK increased yields by 15.2–65.8% and C sequestration by 27.0–64.4%. The rice–wheat rotation gave the highest yield and biomass C (5.27–12.59 t ha−1 yr−1), whereas the lowest biomass C was recorded in the broad bean–maize rotation (3.40–7.72 t ha−1 yr−1). The crop rotation at the site served as a C sink with a significantly higher SOC sequestration potential in the manure treatments. The observed SOC sequestration rates were lower than values commonly reported for flooded rice paddies, which is probably due to lower inputs of C especially in the broad bean–maize rotation and also in the cotton–barley rotation.