Classification of Certain N Traits as Criteria for the Identification of Productive Maize Genotypes1

Abstract

In the past 30 years the increase in maize (Zea mays L.) yields has not been proportional to increased N use. The isolation of genotypes that are better able to utilize N fertilizer to produce higher grain yields would improve this relationship. The purpose of this study was to determine if maize genotypes with a higher concentration of reduced N in the leaves during the early grain‐fill period are more productive. A series of 20 S1 SSS lines developed from cycle 3 of a phenotypic recurrent selection program for high and low nitrate reductase activity (NRA) were crossed to the testers B73, H96, N28, and Mo17. The hybrids were evaluated in 1980 for NRA and total reduced N concentration (RN) in leaves at 10 and 20 days after anthesis. Based on the data, four classes of genotypes were developed: high NRAhigh RN, high NRAolow RN, low NRA‐high RN, and low NRAlow RN. The four classes were evaluated in 1981 and 1982 in replicated field trials. The initial classification of genotypes for high and low NRA or RN in 1980 was reproducible when the four classes were grown in different environments in 1981‐1982. The high RN genotypes had greater grain yields than the low RN genotypes. The low NRA genotypes also showed a yield advantage over the high NRA; however, the low NRA was associated with high RN. The low NRA‐high RN class had significantly greater yields in 1981 and 1982 than the other three classes. The high RN class compared with the low RN class had higher yields (10.5%), lower grain moisture at maturity, silked 2 days later, produced more kernels (6%) that were smaller (by weight 4%) and deposited dry matter in the grain at a faster rate (20%) from 35 days after anthesis to maturity.