Recovery of soil nitrogen by maize at various soil depths: a field study using 15N-labelled fertiliser nitrogen

Abstract

Nitrogen (N) recovery by maize (Zea mays L.) in harvested grain is typically only 30–45% of applied fertiliser N, with the remainder susceptible to leaching and denitrification. In New Zealand, nitrate-loss regulation has increased reliance on nutrient budgeting models such as OverseerFM®, which until recently assumed a maximum effective maize rooting depth of 60 cm, potentially under-representing N uptake by deep-rooted crops, e.g., maize. Using 15N labelled fertiliser, maize uptake, timing and partitioning of absorbed N from soil depths of 60, 90, and 120 cm were assessed under New Zealand field conditions. A two year field experiment was conducted on a Waikato allophanic soil, with 15N applied at the V6 growth stage via subsurface injection beneath individual plants. Plant tissues were sampled through to maturity
to trace depth specific uptake and redistribution. Recovery of 15N in aboveground biomass mostly occurred post-silking, and was 65-69%. Results show that maize can access soil N from ≥120 cm depth, supporting improved representation of deep rooting and late-season N uptake in nutrient budgeting models.