Nitrogen fertilizer effect on grain amaranth

Grain amaranth (Amaranthus spp.) is an ancient crop that is now receiving fresh attention. This has led to a demand for crop management information, including that on N fertilization. This study evaluated the effect of N fertilizer on amaranth grain yield, yield components, and growth and development. The study was tarried out in three Missouri environments with five levels of N fertilizer (NH4NO3 broadcast preplant at 0, 45, 90, 135, and 180 kg N ha(-1)) and three cultivars (Plainsman, D136, and K266). Averaged across cultivars and environments, N fertilizer at the top rate of 180 kg N ha(-1) produced a yield increase of 42% relative to plots receiving no N fertilizer. Yields were consistently improved by additions of 45 and 90 kg N ha(-1), but additional N fertilizer above the 90 kg N ha(-1) rate increased yield in only one out of three environments. At the one site where yield components were evaluated, yield differences were due to increases in seed number per plant, since seed weight and plant population at maturity were unaffected by N fertilizer rate. Plots with high rates of N fertilizer had later maturity, as indicated by time of flowering and seed moisture. Average moisture of seeds harvested from plots receiving 180 kg N ha(-1) was 320 g kg(-1), while seeds from plots with no N fertilizer had 240 g kg(-1) moisture. Comparing the same high-N treatment to the control with no N showed height increases of 14, 24, and 44% in the three environments. Although amaranth yield is responsive to N fertilization, high rates of N fertilization can negatively affect grain harvest in terms of excessive plant height, increased lodging, and delayed crop maturity.