Abstract

Knowledge of the pattern of nutrient uptake and loss and the within-tree allocation of nutrients in trees is critical to the understanding of ecosystem nutrient fluxes and to the management of applied nutrients in agricultural ecosystems. Fluxes of nutrients in whole trees and determination of total annual uptake, nutrient allocation within organs and loss in annual organs were obtained in a mature commercial almond (Prunus dulcis) orchard managed with non-limiting irrigation under varied nitrogen (N) and potassium (K) fertilization regimes from 2008 through 2012. Whole tree nutrient dynamics were derived from multiple in-season measurements of nutrients in leaves and fruits and biomass in all years. Whole tree nutrient budgets in perennial tree parts were derived from whole tree excavations and tree coring in 2011 and 2012 when the orchard had reached >85% full canopy closure. The annual N increment in perennial tree organs was 21kg, 41kg, 44kg and 45kgha-1 for the four N application rates of 140kg, 224kg, 309kg and 392kgha-1 N, respectively. In this orchard maximum agronomic productivity (yield plus increment in tree size) was recorded with an N application rate of 309kgha-1. Under optimal N application the annual increment in P, K, Ca and Mg was 8kg, 38kg, 3.5kg and 2.8kgha-1. Total N in leaves in midsummer in 2012 (a low yield year) was 37kg, 43kg, 54kg and 58kgha-1 for the four N application rates. In contrast, total N in leaves at mid-summer in 2011 (high yield year) was 21kg, 28kg, 35kg and 39kgha-1 for the four N application rates. In years 2009 through 2011 nitrogen in fruit at harvest represented 90% of whole tree N fluxes. In trees provided just adequate N to achieve maximal yield (309kgha-1 in this experiment in years 2009-11), N, P, K, S, Ca and Mg export in fruit was 212kg-366kgha-1, 26kg-45kgha-1, 265kg-389kgha-1, 7.9kg-14.4kgha-1, 24.7kg-29.6kgha-1 and 15.9kg-22.6kgha-1, respectively. The majority of whole tree macro and micronutrient uptake occurred between anthesis and kernel fill with 35-50% of total N uptake occurring before 40 days after full bloom (DAFB) and 80-90% of the total N being accumulated by 112 DAFB coinciding with kernel filling. Over 70% of the total P and 65-80% of the total K was accumulated in fruits by mid-season. Ninety percent of total S, 80-90% of total Ca and 70-85% of total Mg accumulated in fruit by 112 DAFB. The findings from the study can be used for in-season fertilizer management according to plant demand based on expected yield.