Potential N mineralization and availability to irrigated maize in a calcareous soil amended with organic manures and urea under field conditions

Quantification of the Nitrogen (N)-supplying capacity of organic manures provides an important insight into more effective N management practices. The aims of this study were to determine the potential N mineralization of cow manure (CM), poultry manure (PM), urea fertilizer (UF) and the combined use of cow manure + urea fertilizer (CM + UF) for silage maize (Zea mays L.) in a calcareous soil under field conditions. Selected soil samples were collected after different N sources application, and mineral N (NO3--N and NH4+-N) was determined for a total of 110 days of field incubation, using the buried bag technique. Poultry manure-treated soils had significantly higher total N mineralization (244 kg ha-1) than CM (109 kg ha-1), UF (138 kg ha-1) and CM + UF (141 kg ha-1) treated soils. However, N availability was greater in UF (69%) and PM (61%) treated soils than that of CM + UF (47%) and CM (28%) fertilized soils. Shoot dry matter of maize and N uptake were considerably higher in PM treated soil than in UF, CM and CM + UF soils. Nevertheless, maize N recovery was significantly higher in urea soils (60%) than in PM (42%) and CM + UF (37%) soils followed by CM soil (15%). In conclusion, our data indicated that PM and the CM + UF that released N slowly resulted in high maize silage production, N uptake and N recovery following their application in these calcareous soils with low SOM content and N availability.