Recovery of 15N‐Labeled Nitrate Injected into Deep Subsoil by Maize in a Calcareous Alluvial Soil on the North China Plain

Abstract Recovery of residual nitrogen (N) from the subsoil by maize (Zea mays L.) was studied by injecting 15N‐labeled nitrate at 110 cm for treatments with and without N fertilizer in a calcareous soil on the North China Plain. The results show that the recovery of 15N‐labeled nitrate diffusing in the 90‐ to 130‐cm soil horizon was 11.9% with N fertilizer application and 6.7% without N application in maize. Nitrogen fertilizer applied to topsoil stimulated growth of maize roots in the subsoil, thus increasing the recovery of 15N‐labeled nitrate. In the relatively dry growing season in this experiment, the 15N‐labeled nitrate did not move downward because there was no downward water flow at 110 cm. Hence, under dry weather conditions, the maize crop can re‐utilize a small part of the residual soil nitrate in deep soil layers. Most of the nitrogen uptake was in the 0‐ to 80‐cm layer during the experiment.