Long-term Soil Organic Carbon and Crop Yield Dynamics on Cropland in Hilly and Gully Areas of Loess Plateau

Soil Organic Carbon (SOC) is one of the key factors affect agricultural production, nutrient availability, soil stability and the flux of greenhouse gases. The comparison of simulated and observed data of SOC and yields for the period 1998-2008 were conducted in hilly and gully areas of loess plateau. Denitrification-Decomposition (DNDC) model was validated using SOC content and crop yield data collected from long-term experimental sites on Loess Plateau in China. The results showed that DNDC was capable of quantifying SOC and crop yield in the agro-ecosystems in this region. In addition, the DNDC model was used to investigate effects of different fertilization managements on SOC content and crop yield dynamics on the three major croplands for 11 years. Simulated results showed that single manure application or combined with nitrogen fertilizer application could significantly enhance the SOC content and crop yield on all three types of cropland (3.16 or 3.53 g C kg-1, 425.04 or 437.08 kg C ha-1 on the slope land, 3.10 or 3.14 g C kg-1, 366.86 or 517.3 kg C ha-1 on the terraced field and 5.72 or 6.55 g C kg-1, 2808.36 or 2940.40 kg C ha-1 on the flat field, separately). No application of any fertilizer neither contributed to enhancing soil fertility nor increased crop yield. Single nitrogen fertilizer application could increase crop yield 333.84 kg C ha-1 on the slope land and 2616.36 kg C ha-1 on the flat field but could not significantly increase the fertility level of top soil. Sometimes, the single nitrogen fertilizer application even decreased 0.02 g C kg-1 on the slope land. Therefore, the application of manure combined with a certain amount of nitrogen fertilizer would be a better management practice to achieve a goal of increasing soil carbon sequestration and food security.