Nitrogen fertilization management in orchards to reconcile productivity and environmental aspects

Nitrogen fertilization in orchards of Emilia-Romagna Region, (Italy) was based in the past on excessive, not split, applications often supplied late in winter; the NUE (Nitrogen Use Efficiency) was therefore low and the risk of nitrate leaching was high. This paper summarizes the studies conducted in the last 10 years at the Department of Horticulture and Forestry of the University of Bologna aimed to develop a more rational use of nitrogen in orchards and vineyards. Root escavation of mature trees revealed that the use of localized irrigation (drip or microjet) causes a concentration of roots in the area wetted by the emitters. In such a situation, band applications of N to the tree row may allow a reduction of amounts of N fertilizer, while widespread applications, especially if the orchard soil is tilled, lead to an accumulation of nitrates in the alley. Results of several field trials where increasing N rates were applied indicate that the kind of response to N supply depends on the presence in soil of natural sources of nitrogen. This fact clearly stresses the necessity of evaluate the N status of an orchard before N fertilization. Rapid estimation of leaf chlorophyll by portable instruments is a promising index of leaf N concentration, only provided that calibration is made for each cultivar. A method, currently under testing in orchards and vineyards of Emilia-Romagna, is proposed here to adjust N fertilizer rates to the demand of the crop and to the level of available N in soil as determined in soil or soil solution samples. © 1996, Kluwer Academic Publishers. All rights reserved.