Nitrogen and Sulfur Management in Soybean and Edamame Production in the Mid-Atlantic Coastal Plain
Brooks, Keren Ruth
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The United States is a world leader of soybean [Glycine max (L.) Merr.] production, but to maintain quality production at this level, soybean management needs to be continually monitored and improved. Sulfur (S) deficiencies in soybean have become more frequent in the U.S. due to fertilizer purity, emissions regulations, and higher yields. We completed a study for soybean grown in sandy loam soils in the mid-Atlantic coastal plain system to determine proper S fertilizer rate and application timing. Yields ranged from 1,236-4,051 kg ha-1. Neither S rate nor application timing influenced yield. S treatments increased methionine concentration (methionine = -0.0001 S rate2 + 0.002 S rate + 5.60). Sulfur fertilization can improve soybean quality and may impact marketability. Another study was conducted to determine optimal source and rate of S application for soybeans in the Mid-Atlantic coastal plain system. Yields ranged from 1,316-4,914 kg ha-1. While sulfur rate did not influence yield and fertilizer source responses were site-specific. Sulfur leaf tissue concentrations were directly related to S rate (S concentration = 0.004S rate + 2.103). Nutrient uptake responses to S fertility indicate the potential for S yield responses in the future when soils become S depleted and contain less available S. Soybean producers and retailers in the United States are interested in capitalizing on new edamame markets to provide a domestic product. To aid the shift from oilseed production to vegetable production, a study was conducted to determine the optimal N rate and N application timing for edamame yield and quality in the Mid-Atlantic coastal plain system. Nitrogen rate significantly increased yield one out of three years (Yield = 29.9N Rate + 3387) when all N was applied at planting but was not significant with split applications. Fertilizer rate and timing did not impact edamame maturity or final pod/bean quality. N fertilizer applied at-planting may aid edamame yield and profit for sandy loam soils in the mid-Atlantic, USA. Currently, mid-Atlantic coastal plain soils, coupled with S deposition, are able to supply enough S for soybean growth and development, but without fertilization soybean soils are being mined of S and will eventually become depleted. Sulfur must be monitored if future deficiencies are to be avoided. Nitrogen fertilizers may improve yield in vegetable soybean production. Both oilseed and vegetable soybean farmers should continue to monitor soil nutrient levels to ensure proper nutrition for soybean growth and development.
General Audience Abstract
Soybean (Glycine max L. [Merr.]) is a diverse crop used across various industries: from vegetables for human consumption to protein for animal feed or even additives for roofing sealants. The U.S. is a world leader in soybean production. To maintain quality production at this level, soybean management needs to be continually monitored and improved. Sulfur (S) and nitrogen (N) fertilizers are one current area of interest in soybean production and management. This dissertation will discuss both. Historically, acid rain, which contained high levels of S, provided all the necessary S for proper soybean growth and development. In recent years, industry emissions regulations have decreased the amount of S entering the air, thereby decreasing S deposits in acid rain. At the same time, soybean yields are increasing, and higher production requires higher amounts of inputs. Therefore, because S is a necessary input, it is being taken from the soil to meet the needs of high yielding soybean. Less and less S remains in the soil for future soybean crops. This study was conducted to determine proper sulfur fertilizer applications, to ensure quality and quantity soybean production for Virginia farmers. Yields ranged from 1,236-4,914 kg ha-1. Currently, soils contain sufficient S levels for proper growth and development, but if current trends persist sulfur deficiencies will become apparent in the future. Although the U.S. soybean production is abundant, most of the vegetable soybean, also called edamame, consumed in U.S. is imported. The interest in providing a domestic edamame product has led soybean farmers to reevaluate and adapt soybean production strategies to fit a vegetable crop. Edamame is the same species as oilseed soybeans commonly grown throughout the US, but instead of waiting until the seed is dry, edamame is harvested when the seed is still green. This study also was conducted to provide nitrogen fertilizer recommendations for Virginia soybean farmers hoping to adjust their farms to produce quality vegetable soybean. Nitrogen fertilizer improved edamame gross production one out of three years. Continual observation of soil nutrient levels and soybean health is necessary to ensure quality growth and production for both oilseed and vegetable soybean.
- Doctoral Dissertations