Interaction between soil moisture and nitrogen dynamics in the root zone of a pear (Pyrus communis ‘Conference’) orchard

Nitrogen (N) is an essential macronutrient to ensure the quality of ‘Conference’ pears (Pyrus communis ‘Conference’). On the one hand, excessive N fertilization results in N percolation, which contaminates the ground and surface water. Longer periods of drought, as they occurred during the last years, cause a decrease in N uptake, which results in more N percolation in winter. On the other hand, minimizing N fertilization makes it difficult to ensure pear quality. Therefore, the relation between soil moisture and N dynamics was studied. A mineral N balance, coupled to a soil water balance, was used to calculate N dynamics in the root zone. These balances were calibrated with in situ observations (soil water and N content), collected in an irrigated Belgian ‘Conference’ pear orchard. Alongside soil observations, fruit parameters (fruit quality, yield and phenological parameters), stem water potential (SWP) measurements and NDVI (normalized difference vegetation index) images were analysed to identify the impact of drought and to reveal impact on the crop vegetation in two contrasting soil moisture zones in the pear orchard. Although the orchard was fertilized according to good farmers practices, which was 65 kg N ha^‑1 for the entire season, the N balance indicated significant N percolation in the observation period 2019-2020 (56-75 kg N ha^‑1 year^‑1). Total N mineralization (0-40 cm) was responsible for 63-71% of the total N supply in the root zone while fertilization accounted for only 22-28% of the total N input. The N percolation was inherently linked to high soil fertility in the pear orchard. In the drier soil moisture zone, the N percolation was estimated to be 19 kg ha^‑1 higher compared to the more humid zone, which can be explained by a lower crop N uptake due to drought.