CORN ROOT GROWTH and Nitrogen USE Efficiency as Affected by Gypsum and Nitrogen APPLICATIONS Under A NO-till SYSTEM.

Corn (Zea mays L.) crop has a high nitrogen (N) demand to reach large grain yields. The continual rises in nitrogen fertilizer prices, combined with elevate environmental risk of NO₃^- contamination by leaching, leads to the necessity of better strategies to improve nitrogen use efficiency (NUE). A field trial was carried out in Southern Brazil to evaluate the effects of gypsum and nitrogen rates on no-till corn yield and NUE. Treatments consisted in four gypsum rates (0, 5, 10 and 15 Mg ha^-1), combined with four N-NH₄NO₃ rates (0, 60, 120 and 180 kg ha^-1). Gypsum was applied on the soil surface before corn sown and N application was at topdressing, after corn sown. 

The higher corn grain yield (12.9 Mg ha^-1) was achieved by the combination of higher gypsum (15 Mg ha^-1) and N (180 kg ha^-1) rates. In this treatment, the grain yield was 3.6 Mg ha^-1 higher than control. Gypsum improved corn root growth and increased N and Sulfur (S) uptake, resulting in an improvement of 22% in NUE. Closed and positive relationship between corn grain yield and uptake of N (R² = 0.89) and S (R² = 0.64) was obtained. Corn grain yield also had positive relationship with root length (R² = 0.42). The improvement in corn root growth promoted by gypsum application had positive relationship with S uptake (R² = 0.77), although there was no significant relation between root growth and N uptake. The improvement in N uptake was promoted by S uptake (R²=0.50) in corn crop. Since the increase in corn grain yield was due the improvement in root growth and N and S uptake, but N uptake was not affect by root growth, our data leads to the conclusion that the raise in S uptake entails in more N uptake in corn crop.