Long-term organic fertilisers application increase plant autotrophic, soil heterotrophic respiration and net ecosystem carbon budget in a hillslope agroecosystem

The effects of long-term various organic fertilisers application on ecosystem respiration components and net carbon budget have rarely been investigated in a hillslope agricultural ecosystem. Hence, we measured the rates of plant autotrophic (R_a) and soil heterotrophic respiration (R_h) from 2011 to 2012 with five treatments: no fertiliser (CK); mineral fertiliser (MF); MF combined with swine manure (MFS); MF combined with crop straw (MFC), and swine manure (SM). Our results confirm that R_a was found to be more temperature-moisture sensitive than R_h, whereas R_h was more temperature sensitive than R_a. Soil microbial biomass carbon (MBC) is a major factor influencing the temperature sensitivity coefficient of Rh (Q₁₀), thereby application of organic fertilisers combined with mineral fertilisers (MFS and MFC) significantly increased annual by 19.3% and 17.2% compared with MF treatment. Annual carbon emissions via R_h and R_a under MFS, MFC and SM treatments were increased by 24.6, 28.5, 48.8% and 6.6, 10.6, 1.8%, respectively compared with MF treatment (4.6 and 23.2 t C/ha/year). Net primary production (NPP) under MFS, MFC and SM treatments were increased by 5.4, 6.01, and 15.6% relative to MF treatment (13.6 t C/ha/year), respectively, and the corresponding net ecosystem carbon budget (NECB) increased by 121.2, 172.8, and 342.4%. Our findings establish that long-term organic fertilisers application increase plant autotrophic, heterotrophic respiration and net ecosystem carbon budget, which can increase the carbon sink function. Overall, crop straw combined with mineral fertiliser is a feasible agronomy practice to increase carbon sink function, reduce soil erosion and maintain crop yield.