Quantifying the timing asynchrony between soil nitrogen availability and maize nitrogen uptake

In temperate annual cropping systems, an asynchrony between soil inorganic nitrogen (N) availability and plant N uptake is hypothesized to be a major source of poor N fertilizer use efficiency and environmental N losses. However, relationships between the timing of plant N uptake and soil N availability are poorly understood due to a lack of high-resolution time-series measurements. We measured soil inorganic N pool size from 0–30 cm and 30–60 cm as well as maize (Zea mays) N uptake at high temporal resolution throughout the growing season across nine site-years. Using these data, we developed models based on growing degree days (GDDs) to quantify the asynchrony between soil N pool size and crop N uptake We used absolute values (kg N ha−1) and standardized values as a percent of maximum soil and plant N pool sizes for each site-year. The maximum rate of maize N uptake lagged the maximum rate of soil inorganic N depletion by 91 and 185 GDDs for models of absolute and standardized data. By the cessation of maize N uptake, soil inorganic N pool size declined to < 20% of initial values (< 35 kg N ha−1). Our data provide a valuable resource to quantify and reduce asynchrony between soil N availability and maize N demand. The models developed herein can transfer across other locations. To improve N fertilizer management.