Effects of Harvest-Aids on Seed Nutrition in Soybean under Midsouth USA Conditions

Interest in using harvest aids (defoliants or crop desiccants) such as paraquat, carfentrazone-ethyl, glyphosate, and sodium chlorate (NaClO3) have become increasingly important to assure harvest efficiency, producer profit, and to maintain seed quality. However, information on the effects of harvest aids on seed nutrition (composition) (protein, oil, fatty acids, sugars, and amino acids) in soybean is very limited. The objective of this research was to investigate the influence of harvest aids on seed protein, oil, fatty acids, sugars, and amino acids in soybean. Our hypothesis was that harvest aid may influence seed nutrition, especially at R6 as at R6 the seeds may still undergo biochemical changes. Field experiments were conducted in 2012 and 2013 under Midsouth USA environmental conditions in which harvest aids were applied at R6 (seed-fill) and R7 (yellow pods) growth stages. Harvest aids applied included an untreated control, 0.28 kg ai ha−1 of paraquat, 0.28 kg ai ha−1 of paraquat, and 1.015 kg ai ha−1 of carfentrazone-ethyl (AIM); 6.72 kg ai ha−1 sodium chlorate, 1.015 kg ai ha−1 carfentrazone-ethyl; and 2.0 kg ae ha−1 glyphosate. Results showed that the application of harvest aids at either R6 or R7 resulted in the alteration of some seed composition such as protein, oil, oleic acid, fructose, and little effects on amino acids. In addition, harvest aids affected seed composition constituents differently depending on year and growth stage. This research demonstrated the possible alteration of some nutrients by harvest aids. This research helps growers and scientists to advance the understanding and management of harvest aids and investigate possible effects of harvest aids on seed nutrition.

Nitrogen fixation sensitivity related to water use efficiency at reproductive development in soybean

Soybean [Glycine max (L.) Merr.] nitrogen fixation is sensitive differentially to drought among different genotypes at different growth and development stages, which directly affects soybean yield. Acetylene reduction activity (ARA) response to a gradual drought and rewatering period at late podding (late R₃) and late seed fill (late R₅) were evaluated in two different water use efficiency (WUE) genotypes. Drought-stressed plants with high WUE (PI 372413) decreased ARA more insensitively than that of low WUE (PI 548534), and drought-stressed plants with low WUE (PI 548534) maintained low ARA level after stress alleviation at late R₅. The recovery ability of N₂ fixation was a genotypic difference with WUE at late reproductive development (late R₅), especially. Analysing relation between fraction of transpirable soil water (FTSW) and relative ARA, it was confirmed that PI 372413 with high WUE was more insensitive to water deficit and had drought tolerance by N₂ fixation and recovery ability with a threshold of 0.139–0.147 FTSW than PI 548534 with a threshold of 0.192–0.209 FTSW. The ability to recover N₂ fixation following drought during the reproductive developmental stage would be of an important value in the actual planting environment.

Seed traits and germination of native grasses and invasive forbs are largely insensitive to parental temperature and CO2 concentration

The structure and function of grassland ecosystems can be altered by a changing climate, including higher temperature and elevated atmospheric CO2 concentration. Previous studies suggest that there is no consistent trend in seed germination and seedling recruitment as affected by these conditions. We collected seeds of two native and two invasive species over 6 years from a field study with elevated CO2 (600 p.p.m.) and temperature (1.5/3.0°C day/night) on the mixed-grass prairie of Wyoming, USA. Seed fill, viability and mass were evaluated and germination tests were conducted under alternating temperatures in growth chambers. Thermal time requirements to reach 50% germination (θ50) and base temperatures (Tb) for germination were determined using thermal time models. Climate change conditions had limited effects on seed fill, viability and mass. The combination of CO2 enrichment and warming increased germination of Bouteloua gracilis. Centaurea diffusa and Linaria dalmatica, two invasive species in this study, had the lowest θ50 and Tb required for germination among all the species studied. Although final germination percentages of these invasive species were not affected by treatments, previous studies reported increased seed production under future climate conditions, indicating that they could be more invasive at the regeneration stage in the future. We conclude that projected future temperature increases will have little effect on seed reproductive traits of native species. In addition, the distribution and abundance of B. gracilis and invasive species may be favoured by global climate change due to enhanced germination or seed production traits caused by elevated parental CO2 and temperature conditions.