Increasing nitrogen cycling in deciduous fruit orchards and vineyards to enhance N use efficiency and reduce N losses – A review

The environmental goals of current agricultural policies in several countries emphasize the need to find strategies for reconciling productivity and fruit quality with the goal of minimizing nitrogen losses in orchards and vineyards. Management techniques that reduce losses involve precisely matching N needs with soil N availability, efficient supply methods and suitable forms of N fertilizer. Moreover, plant N uptake plays an important role, as it removes active N forms from the soil that could fuel N losses. This review, focusing on deciduous fruit trees and grapevines, first frames the issue of N losses in these cropping systems within the context of the nitrogen availability, then focuses on the N cycle both at tree and at ecosystem level. We provide examples of how this knowledge could lead to reduced risk of N losses and enhanced fertilizer nitrogen use efficiency (FNUE). Studies into tree internal N cycling have allowed significant improvement in the optimal timing of fertilizer N supply. Nitrogen cycling at orchard level involves bidirectional transfer of significant amounts of N between the soil, on the one hand, and trees and herbaceous vegetation, on the other. This review proposes a paradigm shift in the way that N use efficiency in orchards and vineyards is considered, whereby the primary goal becomes enhancing the residence time of the N in the system. Under the best-case scenario, most of the soil and fertilizer N should be forced to cycle within the tree or between the vegetation (trees and the herbaceous plants) and the soil. Reaching this goal under different growing conditions and precipitation regimes represents a challenge for both the scientific community and extension services, as well as one of the priorities for an agroecological approach to the N nutrition of grapevines and various deciduous fruit trees species, with special reference to the temperate growing regions.