Dynamics and Sequestration Potential of Soil Organic Carbon and Total Nitrogen Stocks of Leguminous Green Manure-Based Cropping Systems on the Loess Plateau of China

Estimating the dynamics and future sequestration potential of soil organic carbon stocks (SOCS) and total nitrogen stocks (TNS) is useful to determine whether cropping systems can promote sustainable production in terms of improving soil fertility. The Rothamsted Carbon (RothC) model and the correlations between SOCS and TNS were used to estimate the future SOCS and TNS of green manure-based wheat production systems on the Loess Plateau of China. The field study was a split-plot design with 4 main treatments (Huai bean, soybean and mung bean grown as green manure in summer, with a fallow treatment as the control) and 4 subtreatments (synthetic N rates of 0, 108, 135 and 162 kg ha(-1) applied at wheat sowing). Leguminous green manure (LGM) treatments increased the amount of carbon and nitrogen returned to the field by 67-91% and 74-125%, respectively, compared with the fallow treatment (P < 0.05). These treatments also increased SOCS by 15-23% and TNS by 12-22% (P < 0.05) after 8 years in comparison with the fallow treatment. Coupling of the RothC model and the correlations between SOCS and TNS of the 3 LGM treatments generated acceptable simulations for the dynamics of SOCS and TNS. The projected SOCS for LGM and fallow treatments at the new equilibrium are 37.67-47.29 and 13.97-17.58 Mg ha(-1), respectively. The corresponding TNS for LGM treatments are 5.42-6.79 Mg ha(-1). The projection also indicates that under the LGM treatments, the SOCS and TNS at the new equilibrium will be 107% and 158% higher, respectively, than the values prior to the experiment. In conclusion, growing LGM to replace summer fallow would be a useful alternative to improve soil fertility and promote sustainable crop production.