The effect of plant density and nitrogen fertilizer on leaf area, chlorophyll, and grain protein of Zea mays in competition with Amaranthus retroflexus

In order to investigate the effect of plant density and different amounts of nitrogen fertilizer on yield components, leaf area, chlorophyll and grain protein content of Zea mays cultivars and Amaranthus retroflexus biomass, an experiment was conducted in two crop years (2012-2013) in the form of a split plot based on a randomized complete block design with four replications. The main factors included maize cultivars (single cross hybrids 370 and 704) and the sub-factors included different levels of maize densities (60000, 70000, 80000, and 90000 plant ha^-1) and different levels of nitrogen fertilizer including 200, 300, 400, and 500 kg ha^-1. The effect of density on all traits was significant while the effect of cultivar on chlorophyll and leaf area index, and also the effect of nitrogen on the number of ears per square meter were not significant. Maize cultivar 704 had significantly higher number of grain per ear, weight of one thousand grains, and grain protein compared to cultivar 370 but the number of ears was significantly lower than that of cultivar 370 and there was no significant difference in chlorophyll content and leaf area index between the two cultivars. The highest grain protein was obtained at 80000 plant ha^-1 density and application of 400 kg ha^-1 N. Also, cultivar 704 significantly decreased redroot biomass compared to cultivar 370. According to the findings, cultivation of cultivar 704 is recommended with a density of 80,000 plant ha^-1 along with application of 400 kg N ha^-1.