Co-application of glucose and phosphorus with recalcitrant high-carbon soil amendments improves N retention in a reclaimed soil: a long-term incubation study

Incorporation of soil amendments with high organic carbon content (HCA) can reduce losses of mineral nitrogen (N) from agricultural soils. The magnitude of N immobilization and remobilization is strongly controlled by the availability of carbon (C) and phosphorus (P). However, the exact mechanisms and interactions between C, N, and P availability are poorly understood. An eight-month incubation experiment was conducted on recultivated mine soil with low organic C, mineral N and P background concentrations to investigate the effects of HCA in combination with 13C-labelled glucose and mineral P fertilization on greenhouse gas emissions, soil nutrient status (dissolved organic C (DOC), nitrate (NO3-), extractable P), and microbial biomass growth. The experiment had a factorial design of one N level x two P levels x six C treatments (control, wheat straw, poplar sawdust, glucose, and combinations of wheat straw or sawdust with glucose). The HCA increased the cumulative CO2 and CH4 emissions but decreased N2O emission, except for wheat straw. Addition of 13C-labelled glucose decreased the cumulative CH4 emission by 59 and 85 % in the sawdust and sawdust + P treatment, respectively. Glucose application reduced the NO3- content in the HCA-amended soil by 26-64 %, while P fertilizer further decreased the NO3- content in the wheat straw and sawdust treatments by 20 and 24 %, respectively. Both HCA and glucose treatments promoted microbial biomass growth and reduced the soil mineral N content. The delta 13C of microbial biomass (delta 13CMB) showed an increasing trend during the whole experiment, although 13C-labelled glucose was added only once at the beginning of the experiment. Addition of HCA decreased delta 13CMB, while P addition had the opposite effect. In conclusion, adding a readily available C source to HCA may increase the efficacy of retaining N in post-harvest soils, particularly of more recalcitrant types of HCA like sawdust.