Evaluation of Plant Growth and Yield Reduction on Late Planted Soybeans.

Late planting may affect plant growth and yield of soybean [Glycine max (L.) Merr.]. The objective of this study was to evaluate the influence of late planting on length of vegetative and reproductive stages, vegetative growth using optical sensing technology, and yield of maturity group (MG) IV – VIII soybeans. The experiment was conducted at Clemson University, Edisto Research and Education Center (REC), near Blackville, SC in 2008 and 2009. Soybeans were planted approximately every two weeks from April through July. Compared to early planted soybeans, late planting shortened the duration of vegetative and reproductive stages. However, shortening of growth stages was greater for vegetative than reproductive stages, especially for later MG soybeans. Plant growth indices, leaf area index (LAI) and Normalized Difference Vegetation Index (NDVI), mostly decreased with later planting dates, but less decrease was observed for later MG soybeans. Later planting dates significantly decreased yields of all MG soybeans. Compared to grain yield of soybeans planted around 20 May, the estimated grain yield reduction was about 25 kg ha^-1 day^-1 for planting between 20 May and 5 June, 22 kg ha^-1 day^-1 for planting between 3 June and 16 June, and 39 kg ha^-1 day^-1 for planting between 16 June and 2 July. Generally, decrease in vegetative growth and length of mostly vegetative stages contributed to reduced grain yield of late planted soybeans.