NITROGEN POOL ENRICHMENT IN FRUIT TREES FOR SPECIFIC TARGET REQUIRENMENT

I. Klein
Woody perennials, including fruit trees, store nitrogen. The capacity for storage modulates nitrogen uptake and consumption, in accordance with the vegetative and reproductive perennial cycles of the tree. Nitrogen is readily taken up from the soil for immediate consumption and storage in roots, in the bark and in the leaves of evergreen species. Under conditions of sufficient (soil) nitrogen supply, utilization of stored nitrogen is regulated by sink demand and external manipulation of N nutrition is not feasible. In contrast, under N-deficient situations a choice of soil and\or foliar application is available at our disposal to manipulate vegetative and reproductive processes. Manipulations of growth and yield through nitrogen nutrition require the estimation of pool size and the understanding of the dynamics of nitrogen utilization. Nitrogen isotope studies showed that vegetative and reproductive sink strength for available N utilization from external or internal pools are probably equal and greater than the sink strength of the storage pool. Nitrogen is usually stored after the vegetative and reproductive sink demand has been satisfied, within the same year (in the fall), or biennially (in the off year, i.e. in pistachio). Foliar application of nitrogen under sufficiency replaces available soil N, and therefore it is useless. In contrast, foliar application under deficiency has been shown to be beneficial. Traditionally, foliar application has been used to overcome transient N deficiency, and the aim was always to avoid as much as possible a temporary deficiency. In the last decade we were experimenting with apples, applying a different approach, of inducing N deficiency by minimal soil fertilization to achieve certain objectives, and supplementing the demand for N (to avoid yield reduction) by foliar application. The specific objectives were: controlling vegetative growth, reducing N leaching to minimize ground water pollution and improving fruit color. Maintenance of yield was achieved by targeting foliar application for a specific requirement (fruit set), without actually correcting N deficiency. Thus, foliar urea application in the spring and the fall maintained yield of nitrogen deficient apple trees. In contrast, an equivalent summer urea application, which was not targeted for specific usage did not maintain yield.
Klein, I. (2002). NITROGEN POOL ENRICHMENT IN FRUIT TREES FOR SPECIFIC TARGET REQUIRENMENT. Acta Hortic. 594, 131-137
DOI: 10.17660/ActaHortic.2002.594.12
https://doi.org/10.17660/ActaHortic.2002.594.12
leaf analysis, chlorophyll, apple, nitrogen deficiency, foliar spray
English

Acta Horticulturae