Submitted to: Agronomy Journal
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/28/2005
Publication Date: 6/17/2005
Citation: Bruns, H. Arnold, 2005. Ultra-High Plant Populations and Nitrogen Fertility Effects on Corn in the Mississippi Valley. Agronomy Journal. Volume 97:1136-1140 Interpretive Summary: Ultra-High plant populations (29000, 33500, 37500, and 41700 plants/A) and nitrogen fertility treatments (100 lbs/A pre-plant, 200 lbs/A pre-plant, or 100 lbs/A pre-plant + 100 lbs/A at the 6th leaf growth stage) were studied in furrow irrigated corn grown in the Mississippi Delta using 30-inch and 40-inch row spacings. The 30-inch spacing site was a silty clay soil, planted the third week in April of 2002 and 2003 and the 40-inch site was a fine sandy loam soil, planted the first week in April both years. Planting corn at more than 29,000 plants/A in either 30- or 40-inch rows does not increase yields. Also, no advantage in yield or economic return per acre was realized from plots receiving the split application of nitrogen fertilizer over those receiving 200 lbs/A pre-plant. The 100 lb/A pre-plant only treatment did produce less grain 3 out of 4 times and demonstrated a potential yield loss if the side-dress nitrogen application at the six leaf stage is missed. Aflatoxin levels tended to increase with increased plant populations only on corn grown at the 30-inch site. The stress brought on by increased populations likely magnified stresses being experienced by plants at the 30-inch site and not at the 40-inch site, due to the silty clay soil and/or later planting. Fumonisin levels were also higher at the 30-inch site than the 40-inch site. Nitrogen fertility had no effect on aflatoxin or fumonisin in this experiment. Based on these data and previous research, the optimum plant population for a modern corn hybrid grown in the Mississippi Delta appears to be about 28,000 plants per acre.
Technical Abstract: The maximum plant population for newer corn (Zea mays L.) hybrids grown in both 76-cm and 102-cm row spacings in the mid south USA has yet to be firmly established. Pre-plant N fertilizer applications compared with the standard split application method and their effects on corn agronomic characteristics and grain mycotoxin contamination were examined. Four resulting plant densities (71760, 82160, 92560, and 102960 plants ha-1) were grown in plots of eight 76-cm wide rows, 9.1 m long at Site NR (a Dundee silty clay soil) and 102-cm wide rows at Site WR (a Beulah fine sandy loam soil). Three N-fertility treatments were used (112 kg N ha-1 pre-plant, 224 kg N ha-1 pre-plant, and 112 kg N ha-1 pre-plant + 112 kg N ha-1 side-dressed at V6). Maximum yields occurred at 71,760 plants ha-1 at both sites. No yield advantage to planting in 76-cm rows vs. 102-cm rows occurred in this experiment. Stalk lodging increased with increased plant density while kernel weights declined. Based on these data and previous research the optimum plant density for corn in the Mississippi Delta is about 70,000 plants ha-1 regardless of row spacing. No significant differences in yield between the 224 kg N ha-1 pre-plant treatment and the split application N fertility treatment occurred. Yields were generally lower with the 112 kg N ha-1 per-plant only treatment. Data on mycotoxins were inconclusive. Aflatoxin levels were higher at Site NR than Site WR and are likely related to differences in soil series and planting date between the two sites.