Maize Response to Nitrogen: Timing, Leaf Variables and Grain Yield

The main factors determining plant growth and productivity are decisive to be understood since they contribute to maximize plant nitrogen use efficiency. Thus, more reviews related to the correlation between the real content of chlorophyll and real carotenoids with the values obtained by chlorophyll (SPAD) in the early development stages of the maize are important to be obtained. The relation between the maize crop responses to the nitrogen fertilization at different development stages is of fundamental importance as well. The primary objective of this study was to investigate the responses of maize to the nitrogen application, urea fertilizer (15N), in side-dress at different development stages. The secondary objective was verifying the correlation between chlorophylls and carotenoids with SPAD index and these with total biomass (BM), harvest index (HI), grain yield (GY) and grain N content in response to the nitrogen side-dress at different development stages. The nitrogen fertilization was carried out in plots, with the application of 30 kg ha-1 of N at planting and 140 kg ha-1 N as side-dress at vegetative stages V4, V6, V8, V10, and V12, without incorporation into the soil, and control treatment consisted of non-nitrogen side-dress application was also utilized. The 2011/2012 season presented higher precipitation than 2012/2013. Maize crop responded similarly for GY to the nitrogen application in side-dress in both seasons, however, the nitrogen application in the early stages caused higher values for leaf variables, leaf pigments, and SPAD. Higher amount of nitrogen in all parts of the plants was observed in the 2011/2012 season than in 2012/2013, influenced by the adequate weather conditions at the nitrogen application moment. Grain N content from 15N 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 was positively correlated (P < 0.05) with grain N content, GY, and BM, and total chlorophyll at V16 was positively correlated with GY and grain N content. However the chlorophylls a and total, evaluated at V14, were negatively correlated with GY. So, measurement of real chlorophyll and carotenoid pigment contents should be done after V14 stage when studies aim to evaluate crop nutritional conditions and prescribe future grain production practices.