Ultra-High Plant Populations and Nitrogen Fertility Effects on Corn in the Mississippi Valley

Populations for high yield and low mycotoxin levels in furrow-irrigated corn (Zea mays L.) have yet to be firmly established for the Midsouth USA. Preplant N applications compared with a split application and the effects on yield, yield components, and mycotoxin levels were also examined. Experiments were conducted at Site WR (102-cm-wide rows, Beulah fine sandy loam) and Site NR (76-cm-wide rows, Dundee silty clay). Plant densities of 71760, 82160, 92560, and 102960 plants ha-1 were grown in eight-row plots, 9.1 m long at both sites. The N fertility treatments were 112 kg N ha-1 preplant, 224 kg N ha-1 preplant, and 112 kg N ha-1 preplant + 112 kg N ha-1 sidedressed at V6 (six leaves). Yields at Site WR did not differ among populations. Maximum yields at Site NR were at 71760 plants ha-1 (10.3 Mg ha-1) and then declined (b = -0.5065). Kernels per ear declined (b = -40.09 and b = -42.69), kernel weights declined (b = -0.4328 and b = -0.8172), and stalk lodging increased (b = 0.0103 and b = 0.0251) with increased populations for Sites WR and NR, respectively. These and previous data place the maximum population for corn in the Midsouth at about 70000 plants ha-1. No differences in yield occurred between the 224 kg N ha-1 preplant treatment and the split application of N. Yields were generally less with 112 kg N ha-1 per-plant only. Aflatoxin and fumonisin levels at both sites were unaffected by plant population of N fertility.