Quantifying Foliar Nitrogen Effects on Soybean Relative Maturity, Grain Yield, and Grain Quality.

Increasing soybean (Glycine max Merr.) yield is a major objective for Ohio farmers, and supplementing soybean nodulation with synthetic nitrogen (N) has been suggested as a possible management strategy in high yield-potential environments. The objectives of this experiment were to (i) examine the effect of foliar N application at the R3 growth stage (beginning pod) on biomass and relative maturity progression for multiple soybean cultivars, and (ii) quantify effects of an R3 foliar N application on harvest moisture, grain yield, and quality. A field study was conducted in 2016 at two Ohio locations using a randomized complete block design with a full factorial of inoculated soybean variety (three group II and three group III cultivars) and foliar treatment (foliar N application of 2.6 kg N ha^-1 and untreated). Harvest maturation was evaluated using normalized difference vegetation index (NDVI) and visual quantification of 95% brown pod. Grain yield and moisture were quantified at harvest, and grain samples were analyzed for protein, oil, and fiber content. Regardless of location, NDVI values resulted in a sigmoidal curve that may be used to characterize senescence remotely (P<0.001), and leaf senesces was not delayed due to the foliar N application. Across varieties, grain yield was unchanged at one location and decreased at another after foliar N application. Grain moisture, protein, oil, and starch, while different among varieties (P<0.001), was not altered due to the foliar N treatment. Plant N concentration was also not increased at R5 following the application of foliar N. This research is being repeated in 2017 to validate the results. This research will impact soybean producers directly through evaluation of a novel management practice, but will also provide insights into the use of technology to remotely quantify physiological qualities of soybeans, application in optimized management, and selection criteria for plant breeding.