15N-Labelled Fertilizer Recovery by Sweet Sorghum in Mediterranean Climate

A 15N-labelled fertilization trial was carried out on sweet sorghum, grown in semi-arid environments of southern Europe with the aim to monitor the efficiency and effectiveness of the N-fertilisation technique under irrigation and different nitrogen fertilization rates, in factorial combination. A rainfed condition was compared with a full irrigation treatment (100% restoration of total crop water consumption), in a similar way, an unfertilized control was tested with respect to N application rates of 60 and 120 Kg ha-1, respectively. The fertilisation efficiency measured directly through the isotope discrimination technique was on average equal to 15%. The aliquot of nitrogen released by the fertiliser into the soil and not absorbed by the plant becomes part of the different components of the soil nitrogen balance, regardless of its origin.