Rev. Bras. Ciênc. Solo.2007;31(4):731-8.

ISSUE Cover

Nitrate concentration as a complementary indicator of soil nitrogen availability to corn

Lisandro Rambo, Paulo Regis Ferreira da Silva, Cimélio Bayer, Gilber Argenta, Mércio Luiz Strieder, Adriano Alves da Silva

01/Aug/2007

DOI: 10.1590/S0100-06832007000400014

Nitrogen fertilization applied as sidedressing in corn can be optimized by considering additional soil characteristics as complementary indicators of soil N availability. The objectives of this study were to evaluate the potential use, critical level and best sampling time of the soil nitrate (NO₃^–-N) concentration to predict soil N availability in corn, as well as to verify if the determination of the soil ammonium (NH₄⁺-N) concentration, in addition to NO₃^–-N concentration, enhances the efficiency of N availability evaluation. A field experiment was conducted in two growing seasons (2002/03 and 2003/04) in Eldorado do Sul, state of Rio Grande do Sul, Brazil. Different levels of soil N availability were simulated by the application of five N rates (0, 50, 100, 200, and 300 kg ha^-1) 20 % at sowing and the rest sidedressed at V3. The experiment was structured in a randomized block design with four replications. NO₃^–-N, NH₄⁺-N and soil mineral N (NO₃^–-N + NH₄⁺-N) concentrations in the 0-30 cm soil layer at V3, V6, V10 and at silking, as well as corn grain yield were evaluated in both growing seasons. In general, NO₃^–-N soil concentrations were sensitive to the applied N rates, mainly in V6 when the best relationship between NO₃^–-N and corn grain yield was found. The critical level of soil NO₃^–-N concentration, above which a response to N application is unlikely, was estimated at 20 mg kg^-1 in the studied soil, at growth stage V6. The determination of soil NH₄⁺-N concentration, in addition to soil NO₃^–-N concentration, improved the prediction of N availability. A better relationship of soil mineral N (NH₄⁺-N + NO₃^–-N) than of NO₃^–-N concentration with corn grain yield was observed. These results indicate that the development of kits for instant determination of soil mineral N concentration is necessary. NO₃^–-N and NH₄⁺-N as complementary indicators of soil N availability for corn appear promising and studies should be developed under different climate and soil conditions to adequate their use to the management of sidedressed N in corn.