Interaction of Air Temperature and Nitrogen Supply On Root Growth and Nitrogen Uptake by Corn.

Simulation of nitrogen (N) demand and uptake in plant models should account for plant growth rates and soil N availability.  The goal of this study was to quantify root growth and N uptake by corn plants (maize) as affected by air temperature and N supply.  Corn plants were planted in outdoor growth chambers in which temperature, humidity, and CO2 concentrations were precisely controlled.  Four different N levels (2, 6, 8, and 12 mM applied in drip irrigation) combined with two different temperature regimes (25/19 and 31/25 C, day/night) were applied to the corn plants using 4 chambers.  Polyvinyl Chloride (PVC, 152.4 mm in diameter and 762 mm in length) tubes filled with sand (710 mm in length) were used for this study.  Over the growing season, six destructive harvests were carried out.  The sand columns and roots were sampled at every 127 mm of depth to measure the depth distribution of the nitrogen and roots.  Corn plants were separately collected, dried, and analyzed for the Carbon to Nitrogen (C:N) ratio and leaf, stem, ear, and root dry weights.  The C:N ratio of the root ranged from 15 to 72, was higher under low temperature, and was higher for the lower N application rates.  The Root to Shoot ratio (R:S ratio) in corn ranged from 0.1 to 1.1, and was higher under low temperature.  The corn development rates were significantly affected by temperature.  Nitrogen uptake and dry matter were significantly affected by N application rate but not temperature.  The results suggested that nitrogen demand could be modeled using growth rate and knowledge of minimum N content in the plant.  The data from this study will be used to test the root growth model and N uptake model for MAIZSIM.