Precise Fertilization by a Mass-Balance of the Seasonal Changes in Nutrient Uptake by Almond Trees

Abstract

Mineral fertilization through irrigation (fertigation) could optimize resource allocation and eliminate wastes in agriculture. Nevertheless, the fertigation of almond plantations is currently inefficient (50% nitrogen (N) recovery by yields) due to the limited empirical data to support field applications. For precise fertigation in horticulture, we aimed to determine the trees’ actual mineral uptake. We hypothesized that the mineral requirements depend on physiological development and would vary during the growing season as phenology shifts. To investigate this, we tracked the water, N, phosphorus (P), and potassium (K) mass-balances of almond trees in 1 m3 lysimeters and monitored their physiological performances. By canopy coverage (leaf area index—LAI)) and radial stem growth, we determined that almond trees invest in biomass between April and July (northern hemisphere). Then, for August until November, the almond trees accumulated metabolites and minerals for the succeeding winter dormancy. Annually, almond trees can utilize major N applications (~180 kg h−1) in early summer for vegetative growth, extract P (~50 kg h−1) by mid-summer for metabolic translocations, and accumulate K (>250 kg h−1) in late summer, possibly for osmotic compensations. Converting these realizations for farm conditions requires the further characterization of the mineral availability at the root zone, and the nutritional status of trees, under various field fertigation applications.