Nitrate leaching in potato: a comparison between compost fertilized soils and conventional N management

Nitrate leaching to aquifers is a crucial problem in crops with low N use efficiency like potato: an accurate estimate of crop N needs and the soil availability is important to minimize the amount of unused fertilizer in the topsoil and essential for limiting N loss to the watertable, which mainly occurs after potato harvest. Potato cv. Agata was planted in semi-controlled environment (lysimeters) in Padova . The experiments used 3 types of compost in Padova C1, C2, C3 ( with different organic matter origin), each supplying 200 kgha-1, and an unfertilized control. The same cultivar Agata was used in Udine, trt involved the distribution of C1, organic dried poultry manure fertilizer, and mineral fertilizer, and the unfertilized control. Each treatment was twice replicated and the experiment was run for two years. Nitrate content in percolating water was analyzed. Severe meteorological conditions occurred in the first year (very hot temperatures and low rainfall); rainfall and temperatures were in line with the seasonal mean in the second. A remarkable difference between the sites was recorded for total rainfall between April 2003 and March 2005, ranging from 1578 mm (Padova) and 3585 mm (Udine), and in terms of total leachates (ranging between 278 mm to 1520mm) accounts for the large dissimilarity between N loss through leaching in Padova (ranging between 18 kg N-NO3 ha-1 and 38 kg N-NO3 ha-1 ) and Udine (scattered between 127 and 154 kg N-NO3 ha-1). Conventional Fertilizer practice was found to release the highest amount of N among treatmens. Nitrate leaching results of these experiments show that the risk of leaching associated with the use of these composts is comparable to the unfertilized control: less relevant than with mineral fertilizer (-21%), despite being very dependent on soil and climatic conditions.