Contribution of three manures to nitrogen nutrition of potato crop

The manures are usually considered as an important source of nitrogen. However, if they are applied to annual crops without addition of inorganic N, the effect on yield and on N uptake by plants is often very poor. On the other hand, the potential risk of nitrate leaching to water resources is great, due to the temporal lack of adjustment between the N released and plant needs. The main obstacles to the rational utilization of manures are related to the variability of their composition and to their decay process in soils, which make difficult to predict both the time and amount of N released from manures. This study was conducted to evaluate the behaviour of three manures and urea as sources of N for potato, which is considered to be a crop particularly responsive to manures. The tuber dry weight (TDW), the N uptake by tubers and the apparent N recovery (ANR) of added N were compared. The reliability of results was checked through plant analysis and field measurements of N mineralization using an in situ incubation technique