In the Deep South there is an option to attempt to produce to maturity a second, late summer or fall-planted crop following the harvest of a spring-planted crop, such as field corn. This has become named the Ultra-Late Soybean Production System (USPS), the model is to plant indeterminate soybean varieties which are in Maturity Groups (MG) IV-VI that will carry out a normal life cycle in a shortened growth period prior to first frost.
The two universal components of maximizing soybean yield include managing for 1) the number of seeds per pod (and cumulatively on the plant) and, 2) the average seed size (or weight). This USPS system is challenging for producers as the shortened season, often ended suddenly by a killing frost, results in lost yield potential. The lost yield potential follows an expected reduction in the number of seeds per plant because of a) the shorter vegetative growth period resulting in shorter plants which thereby results in less nodes at which flowers and pods may form, b) a shortened reproductive period which reduces seed number and seed weight. Additionally, the shortened plant reduces harvest efficiency because many of the mature pods with larger seed are close to the soil surface below the combine table.
One possible answer to the challenge of producing tall, high yielding varieties with sufficient height is the Long Juvenile (LJ) genetic trait that has been bred into soybeans. These LJ varieties exhibit a recessive gene unlike determinate or indeterminate varieties by having an extended vegetative period, or delayed flowering, when grown in short day length. This results in greater plant height and delayed maturity compared to the commercial varieties on the market. Indeed, LJ soybeans are not bred for U.S. commercial seed because of the difficulty in combining desirable traits with the LJ trait, although the trait has had success in lower latitude growing regions, such as Mexico and Brazil. A few LJ varieties bred by Clemson, namely Agustina, were entered into recent GA-OVTs, returning comparable yields to commercial entries.
Late-planted soybeans in the southeastern U.S. are known to have greater protein concentrations compared to full-season soybeans, at the sacrifice of oil content. While protein content is not currently a factor in grain evaluation for grain sales benefitting farmers, it is an important factor in livestock feed production, with the potential for this to create premiums in high protein soybean grain in the future. There is a need to understand how these late-planted soybeans, both LJ and commercial lines compare in the USPS for protein content.