Matching the Optimum Plant Density and Adequate N-rate with High-density Tolerant Genotype for Maxmizing Maize (Zea mays L.) Crop Yield

Increasing plant density and improving N-fertilizer rate along with the use of high-density tolerant genotypes would lead to maximize maize grain productivity from unit land area. The objective of this investigation was to match the functions of optimum plant density and adequate nitrogen fertilizer application to produce the highest possible yields from unit area with the greatest maize genotype efficiency. A split-split plot design in randomized complete blocks arrangement with three replications was used for yield evaluation across two seasons (2012 and 2013). Main plots were assigned to three N-rates viz., 0 (LN), 120 (MN) and 240 (HN) kg/feddan; fed) (one fed = 4200 m2). Sub-plots were assigned to three plant densities viz., 20,000 (LD), 30,000 (MD) and 40,000 (HD) plant/fed and sub-sub plots to 23 maize genotypes (6 inbreds, 15 diallel F1 crosses made among these inbreds and 2 check hybrids). Nine environments (E) had therefore been created (3 plant densities × 3 N levels). In general, the highest grain yield/plant (GYPP) was obtained from HN with LD (E1), while the highest grain yield/fed (GYPF) was obtained from HN with HD (E3). The environment LN and HD (E9) showed maximum reductions (70.9% and 67.6% in GYPP and 55.5% and 49.6% in GYPF for inbreds and hybrids, respectively) as compared to E1 as a result of both stresses (LN and HD). These reductions in grain yield were associated with reductions in all yield components like number of grains/plant (GPP), ears/plant (EPP), 100-grains weight (100-GW), harvest index, total dry matter, chlorophyll concentration index (CCI) and penetrated light; with maximum reduction in (GPP) and CCI. On the contrary, both stresses together caused increases in barren stalks (BS), anthesis-silking interval (ASI) and economic nitrogen use efficiency (NUEe); with maximum increase in E9. The relationships between the nine environments and GYPF showed near linear regression function for inbreds L54, L29 and L55 and hybrids L18×L53 and L18×L55 with an optimum density of 20,000 plants/fed and N-rate of 240 kg N/fed and a curvilinear regression function for inbreds L17, L18 and L53 and the rest of hybrids with an optimum density of 40,000 plants/fed combined with N-rate of 240 kg N/fed. We could maximize GYPF in the present study to 60.4 ard/fed (one ard = 140 kg) for L17×L54 and 58.7 ard/fed for L17×L18 by using the high density and high N-rate; with a significant superiority in GYPF over the best check cultivar (SC-10) under E9 environment of 26.9% and 23.3%, respectively. The highest yielding genotypes under high-density in this study are characterized with one or more of adaptive traits to high-density and/or low-N.