Does the C:N ratio suffice to predict carbon and nitrogen mineralization dynamics in an arid agroecosystem soil amended with compost?
Résumé
Assessing the mineralization dynamics of composts applied to the soil provides knowledge about nutrient release to growing crops. This research aimed to assess carbon (C) and nitrogen (N) mineralization dynamics of two composts with contrasting nutrient content applied to the soil of an arid agroecosystem. Compost C2 was based only on date palm residues and rock phosphate, while compost C4 combined date palm residues with sheep manure and rock phosphate. An unamended soil was used as a control. The addition rate of compost was standardized to 4 g C per kg of dry soil. Treatments were incubated under laboratory conditions of 25 °C and a soil water content of 60% of field capacity for 91 days. C and N mineralization were assessed through periodic measurements of CO2-C emissions and inorganic nitrogen (NH4-N and NO3-N) in soil extracts. Application of compost C2 induced higher C mineralization over the entire incubation period, followed by C4-amended soil and the control. After incubation, the cumulative CO2-C emission of compost-C2- and compost-C4- amended soil was 1561.4 and 1271.1 mg kg−1, respectively, given the high cellulose and low lignin content in compost C2. The total percentages of mineralized C from compost C2 and C4 were 20.6% and 13.3% of the total added organic C, respectively. Applying compost C2 and C4 to the soil resulted in N immobilization of 176.2 and 26.4 mg kg−1, respectively, while unamended soil supplied 76.1 mg kg−1 of net N mineralized during the incubation. Our findings suggest that the C:N ratio alone is insufficient to predict C and N mineralization from composts. Either compost may be applied in crop rotations to maximize benefits for growing crops.