Nitrogen mineralization in two calcareous soils treated with raw organic amendments

This study examined the mineralization of nitrogen (N) in two calcareous soils (sandy loam and clay soil) treated with the main types of raw amendments, using a laboratory incubation procedure over 40 weeks. At the end of the incubation time, mineralized N in treated soils ranged from 165 to 1,005 mg kg(-1) with sandy loam and from 85 to 1,105 mg kg(-1) with clay soil. The results indicated that poultry manure induced the highest level of N mineralization. In general, the doses of amendments that were applied appeared to present an environment risk of nitrate (NO3--N) leaching, with the exception of the municipal waste compost. In contrast, N immobilization occurred in the two soils amended with wheat and sunflower residues. The N availability characteristics of wheat and sunflower indicated that the accumulation of large concentrations of NO3--N in soil was unlikely to arise from the agricultural use of these materials. The amount of N released from other amendments was high, which indicates that application rates should be reduced, or alternative amendments used, so as to minimize leaching losses in regions where groundwater quality is of concern. The amendments were ranked based on the inorganic N they supplied in the following order: poultry manure > sewage sludge > potato > sheep manure > municipal waste compost. Simple exponential and power models were fitted to all experimental data. These models can be used in describing N mineralization, predicting the amounts of N mineralized over time and in reducing N leaching.