Uses and losses of nitrogen by maize and cotton plants under salt stress

There is no consensus on how much N can be applied to plants under salt stress. In our research we tested the hypothesis that such response depends on salt tolerance of the plant species. So, this study aimed to evaluate the uses and losses of N by cotton (salt-tolerant) and maize (moderately salt-sensitive) irrigated with waters of different electrical conductivity (0.5, 2.0, 4.0, and 6.0 dS m(-1)) and fertilized with nitrogen (60, 100, and 140% of the recommended dose for each crop). We found that nitrogen doses beyond the recommended values exacerbated the negative effects of salinity on growth and photosynthetic rates, especially in maize plants growing under moderate to high salinity. N rates over the recommended dose did not increase leaf nitrogenous compounds, believed to attenuate the negative impacts of salt stress. Our results indicate that the responses to additional nitrogen fertilization depend on crop salt tolerance and on the level of saline stress imposed. Increasing N rates beyond crop needs under salinity only increased leaching losses and reduced the nitrogen-use efficiency, indicating that such practice would result in economic losses and environmental N overload, especially when a supplemental dose is applied to a salt-sensitive crop.