Submitted to: Maydica
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/17/2003
Publication Date: 7/15/2004
Citation: Bruns, H.A., Abbas, H.K. 2004. Effects of harvest date upon maize yield and grain quality in the Mid South. Maydica. 49:1-8. Interpretive Summary: Grain higher than 15.5% moisture is subject to spoilage due to molds. Maize grain harvest in the Mid South is often delayed to field dry grain to a moisture level of 15.5% or less because grain drying facilities are very limited. The effects on yield and grain quality of maize left in the field in the Mid South were documented in this experiment. Three maize hybrids containing the Bt gene for insect control and three hybrids without the gene were grown in 2000 and 2001 and harvested at 14, 28, 42, 56 and 70 days after black-layer. Slightly higher plant populations, irrigation and rainfall during the final 14 days of growth in 2001 resulted in higher yields across all harvests. Grain moisture levels declined with increased delays in harvest. Safe moisture levels of 15.5% or less were acquired by 28 days after black-layer in 2000 and 42 days in 2001. After 28 days in 2000, moisture levels fell below 12% which makes the grain brittle and subject to kernel breakage during harvest and handling. Very little aflatoxin was detected in 2000 with no one hybrid or harvest date having higher levels than any other. No aflatoxin was found in 2001, probably due to rainfall that occurred after the final irrigation that would have relieved or eliminated drought stress during the final 2 weeks of growth. Fumonisin levels though were higher in 2001 than 2000, probably because of the extra moisture. The Bt hybrids did have an advantage with less stalk lodging than the conventional hybrids and stalk lodging did increase as harvests were delayed. Adverse effects on grain yield and quality with delayed harvest appear minimal, but the inherent risks of crop loss due to storms still exist and timely harvesting is still recommended.
Technical Abstract: Limited capacity for artificially drying maize grain exists in the Mid South USA. Most of the area's production is field-dried and thus subject to risks inherent to leaving mature crops in the field. To document the effects of delaying harvest on yield and grain quality, a two-year experiment was conducted at Stoneville, MS. Six maize hybrids (3Bt and 3 non-Bt) were grown in 2000 and 2001. Grain was hand harvested and shelled at 14, 28, 42, 56, and 70 d post-physiological maturity (P-PM). Slightly higher plant populations, irrigation and rainfall during the final 14 d of plant growth in 2001 resulted in higher grain yields that year. Grain moisture levels declined with increased delays in harvest. Levels safe for handling and storage (150 mg g-1) were acquired 28 d P-PM in 2000 and 42 d P-PM in 2001. After 28 d P-PM in 2000 grain moisture fell below 120 mg g-1, and grain became subject to mechanical damage. Declines in grain bulk density after 56 d P-PM may be explained by such mechanical damage. Aflatoxin contamination was minimal in 2000 and non-existent in 2001. Fumonisin levels were higher in 2001 than 2000. In both cases it was probably due to differences in rainfall during the final two weeks of crop growth. Bt hybrids had less stalk lodging than non-GMO hybrids, and lodging tended to increase as harvests were delayed. Adverse effects on yield and grain quality with delayed harvest appear minimal. Inherent risks of crop losses due to weather exist though, and timely harvesting is recommended when possible.