Quantification of Soybean Leaf Senescence and Maturation as Impacted by Soil- and Foliar-Applied Nitrogen

Abstract

Core Ideas • Soybean leaf senescence and maturation, yield, and seed quality were minimally impacted by soil and foliar-applied nitrogen. • Cultivar differences in maturation, yield, and seed quality were evident. • The use of NDVI is an effective technique to describe soybean leaf senescence during maturation. Abstract Ohio producers often question whether fertilizing soybeans [Glycine max (L.) Merr.] with nitrogen (N) will increase yield. Foliar-and soil-applied N have been evaluated throughout the Midwestern US, but few studies have compared the response of commercially available foliar N applications to soil-applied N within the same environments. Additionally, there is limited information on the impacts of N application on soybean maturation and leaf senescence. The objectives of this study were to: (i) evaluate the effect of various rates of soil-and foliar-applied N at different growth stages on the maturation of soybeans; and (ii) quantify the effect on soybean yield and quality (protein and oil) of soil and foliar N application. A field study was conducted in 2017 at two Ohio locations using a randomized complete block design with full factorial of soybean cultivar (one Maturity Group II and one Maturity Group III) and N application treatment (unfertilized control and four N applications varying in source, rate, and timing). The maturity date, yield, and quality varied among cul-tivars. Leaf senescence was impacted by weather conditions to a greater extent than N application. Maturity date was impacted by N application, but all treatments matured within 1 day of one another and were similar to the untreated control. The N treatments had minimal effects on leaf senescence, yield, seed protein, and seed oil. Future studies should focus on expanding these results in additional environments and with more N application treatments. Questions about Nitrogen Fertilization in Soybeans Ohio producers often question if soybean yield can be increased with supplemental N fertilizer application. In high-yield environments (yields greater than 67 bu ac-1), using N fertilizers has been suggested as a practice that may improve soybean yield (Salvagiotti et al., 2008). With more attention being given to environmental stewardship and agronomic sustainability, it is imperative to critically evaluate fertility practices in crops capable of biological N fixation. One possible alternative method to soil applications of N is the use of a foliar N fertilizer. Foliar application may decrease the time for plant uptake and utilization, off-target fertilizer movement , and the quantity of supplemental N needed compared with a Crop Forage Turfgrass Manage. 5:180051. This is an open access article distributed under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).