Nitrogen impacts on maize yield and nutrient use efficiency in contrasting stress environments

Abstract

Nitrogen impacts on maize yield and nutrient use efficiency in contrasting stress environments Nitrogen (N) fertilization and drought stress have large influence on maize grain yield, thus studies about genotypes and management technologies are very important to increase maize production. This study is presented in three chapters; the first two were undertaken in the United States of America and the third one in Brazil. The following objectives are addressed in this order: (1) The primary objective was to understand which traits, if any, differ between similar-maturity tolerant and non-drought tolerant hybrids that govern nutrient uptake and concentrations under different management treatments (varied plant densities (PD) and N rates) and their influence on grain yield (GY). (2) The primary objective was to investigate the physiological and yield responses of comparable-maturity drought and nondrought tolerant hybrids (P1151 vs. P1162, and P1498 vs. 33D49) to varied plant density and N rates. (3) The main objective was to investigate the responses of maize to sidedress N applications, using isotopically labeled urea fertilizer (15 N), at different development stages. The secondary objective was to verify the correlations between the chlorophylls and carotenoids with SPAD index (evaluated at V14 and V16) and all these parameters with total biomass (BM), harvest index (HI), GY and grain N content. The major results for objectives 1 and 2 were as follows: All hybrids had similar GY responses to PD (near 79,000 versus near 100,000 plants ha-1) and N rate (from 0 to 269 kg N ha-1) treatment factors. Hybrid 1 (AQUAmax™ P1151) demonstrated similar leaf photosynthetic (A) and transpiration (E) rates than its non-drought tolerant counterpart of similar maturity since Hybrid 2 (P1162) had a higher leaf area Index (LAI) (at the R2 and R3 stages) and a similar GY as Hybrid 1. Hybrid AQUAmax™ P1498 maintained higher leaf A and E rates than P33D49 during the grain-fill period, thus perhaps demonstrating improved persistence in root water uptake late in the season. There was no single trait differentiation in photosynthesis or transpiration between drought and non-drought tolerant hybrids. Highest BM and GY at maturity generally followed shorter anthesis-silking intervals and more stover macronutrient (P and S) accumulation, in the drought season, so these characteristics appeared to be important drought-tolerant mechanisms regardless of hybrid designations. The major findings from the objective 3 investigations: Maize crop responded similarly for GY to timing of sidedress N application. Grain N content from 15 N fertilizer and N uptake and efficiency were greater for early N applications. SPAD values correlated positively with most pigment variables at V16 in both seasons, thus proving that SPAD was an efficient instrument of indirect evaluation of chlorophylls and carotenoids in maize leaves at early stages. Chlorophyll b at V16, sample stage, was positively correlated (P<0.05) with grain N content, GY, and BM, and total chlo...