Soil Nitrogen Availability after Addition of Thermally Dried Pig Slurry

In the northeast of Spain, the production of large amounts of pig slurry that exceed the fertilization requirements of local field crops is contributing to the deterioration of the soil environment. In recent years, the construction of six treatment facilities has allowed the exportation of nutrient surplus as thermally dried pig slurry (TDPS). Even though it is already used as an amendment, however, little is known about its effect on soil N availability. A long-term aerobic incubation test was used to monitor organic C and apparent N mineralization. Aft er 34 wk, the untreated soil cumulative apparent N mineralization value was 145 mg kg(-1) and the potentially mineralizable N (Theta(N)*) was 196.6 mg kg(-1). In soil treated with 1.6 g kg(-1) TDPS, the Theta(N)* increased by 14% in relation to untreated soil. In soil treated with 4.8 g kg(-1)of TDPS, the Theta(N)* increased by 24%. The similar patterns of the emitted CO2-C and the recovered NO3-N in the untreated soil and TDPS-treated soil show that it is unlikely that significant losses of N occur as gaseous N. It was found that when a low N dose was used, the Theta(N)* was 66% of that added, but only 37% was detected when a higher dose was used. This suggests that, in relative terms, at higher doses there is less microbiological activity than at lower doses. Adding 62.8 mg N kg(-1) as (NH4)(2)HPO4 and (NH2)(2)CO, however, enhanced the mineralization of the soil organic N, providing 20% more N in relation to the untreated soil.