Increasing plant density and improving N fertilizer rate along with the use of high density-tolerant genotypes would lead to maximizing maize (Zea mays L.) grain productivity per 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 per unit area with the greatest maize genotype efficiency. Six maize inbred lines differing in tolerance to low N and high density (D) [three tolerant (T); L-17, L-18, L-53, and three sensitive (S); L-29, L-54, L-55] were chosen for diallel crosses. Parents and crosses were evaluated in the 2012 and 2013 seasons under three plant densities: low (47,600), medium (71,400), and high (95,200) plants ha −1 and three N fertilization rates: low (no N addition), medium (285 kg N ha −1 ) and high (570 kg N ha −1 ). The T × T crosses were superior to the S × S and T × S crosses under the low N-high D environment in most studied traits across seasons. The relationships between the nine environments and grain yield per hectare (GYPH) showed near-linear regression functions for inbreds L54, L29, and L55 and hybrids L18 × L53 and L18 × L55 with the highest GYPH at a density of 47,600 plants ha −1 and N rate of 570 kg N ha −1 and a curvilinear relationship for inbreds L17, L18, and L53 and the rest of the hybrids with the highest GYPH at a density of 95,200 plants ha −1 combined with an N rate of 570 kg N ha −1 . Cross L17 × L54 gave the highest grain yield in this study under both high N-high-D (19.9 t ha −1 ) and medium N-high-D environments (17.6 t ha −1 ).

Maize grain yield response to elevated levels of soil nitrogen is dependent upon genotype of the cultivar. Thus the optimum rate of N-fertilizer differs from maize genotype to another according to its nitrogen use efficiency (NUE). The main objective of this study was to determine the optimum Nrate for each studied inbred and hybrid that maximize grain yield. Six inbred lines of maize differing in their productivity under low-N were crossed in a diallel fashion to produce 15 F1ˊs. Parents and F1ˊs were evaluated in two seasons (2012 and 2013) using a split-plot design in randomized complete blocks arrangement with 3 replications. Main plots were allotted to four N-rates, i.e. 0, 80, 160 and 240 kg N/fed for N1, N2, N3 and N4, respectively. The sub-plots were assigned for the genotypes. Reducing N-level from 204 to 160, 80 and 0 kg N/feddan (fed) [one fed = 4200 m2] caused an increase in days to silking (DTS), anthesis silking interval (ASI), barren stalks (BS), economic NUEe and biological NUEb NUE and a decrease in the remaining studied traits including grain yield and its component. Maximum increase and decrease in traits occurred at N1 level (0 kg N/fed). The inbred lines L17, L18 and L53 proved to be tolerant (T), while L29, L54 and L55 inbred lines were sensitive (S) to N stress. The most tolerant crosses to low-N stress and the most responsive crosses to elevated levels of nitrogen were identified. Only two crosses (L18 × L53 and L18 × L55) showed high tolerance to low-N stress and responsiveness to high-N expressed in grain Original Research Article

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KEYWORDS ABSTRACTThe aim of this study was to assess the combined effects of the three plant growth promoting Rhizobacteria (Azospirillum lipoferum, Pseudomonas fluorescens and Pseudomonas putida) and a biostimulating molecule (chitosan) on plant growth parameters and seeds yield of maize in southern Benin. This study was conducted in reddish ferrous soil with fisher block experimental design. Maize seeds were soaked into chitosan solution for 12 hours and introduced into a seed hole with bacterial suspension. Experimental maize plants were fertilized by half or complete dose of NitrogenPhosphorus-Potassium (NPK) and Urea. Result of the study revealed that the combination of P. fluorescens along with chitosan and half dose of NPK-Urea increased maize height, circumference and seeds yield of 10.18%, 22.05% and 44.10% respectively. Furthermore, the produced biomass increased 71.43% compared to the control in the combination of P. fluorescens, chitosan and complete dose of NPK-Urea. Results of study suggesting that PGPR and chitosan can be used as an effective biological fertilizer combination for increasing maize production under field conditions.

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