Simulation of nitrogen dynamics in an alluvial sandy soil with drip fertigation of apple trees

Abstract

In order to optimize the management of the N-fertilizer inputs with drip fertigation on sandy- silt soil under apple tree orchard cultivation, we observed in situ: (i) the N and water soil transfers, (ii) the N levels in all leaves, fruits and annual shoots, and (iii) the root distribution. Then we used a mechanistic one-dimensional model (WAVE, Vanclooster et al., 1994) to quantify the annual parameters of the water and nitrogen balance on a daily basis. The horizontal heterogeneity along the row of the tree-soil-dripper system has been treated with two adjacent compartments: one under the dripper and receiving fertigation and the other outside this zone. N transfers in the tree make it impossible to estimate directly N uptake by roots over time. The simulated N losses were due to equal amounts of N leaching below 0.9 m deep (9 g N tree -1 year -1 and denitrification (7 g N tree 1 year -1 . The simulated losses of gaseous N were localized predominantly in the compartment under the dripper and showed a higher rate ofleaching during the period ofN input when the wet conditions and the high NO 3 - concentrations were favourable to denitrification. The N-leaching at 0.9 m depth was greatest outside the growing season and was caused by the extension of the N-inputs after the harvest date. This practice, based on the objective to store nitrogen before the period of dormancy does not seem to be justified.