Testing Soybean Yield Response to Sulfur at Planting and Foliar Fertiliziers

Kentucky will collaborate with researchers from Wisconsin, Ohio, Indiana, Minnesota, North Carolina, Arkansas, Louisiana, Virginia and Georgia on a multi-state project to evaluate the response of soybean to sulfur fertilization. Researchers from the land grant university in each of these states will request funding from their State Qualified Soybean Boards (QSSB). Members of this multi-state effort developed the following proposal, Shawn Conley at Wisconsin was the lead author on the original draft, and the text below should be extremely similar to proposals submitted to the other states. Sulfur is an essential nutrient for crop production, often ranked behind only nitrogen, phosphorus and potassium in importance. Increased sulfur removal from higher crop yields, combined with reduced inputs from atmospheric deposition and other sources have increased the prevalence of sulfur deficiencies in some regions of the United States. There is widespread concern about potential sulfur (S) deficiencies in corn and soybeans in the United States. Sulfur is relatively immobile within the plant, so symptoms usually appear in the new growth. Atmospheric deposition used to supply a considerable amount of plant available S (about 8-15 pounds per acre annually), but with the implementation of the Clean Air Act, this amount has significantly decreased. An important source of S is the soil organic matter. When organic matter decomposes, S is released as a sulfate ion into the soil solution. Sulfur is taken up by plants as sulfate, an anion that is mobile in the soil and subject to loss through leaching or volatilization, like nitrate. Sandy and low organic matter soils are at greatest risk for sulfur deficiency. Alfalfa and canola have high sulfur requirements and are more likely to respond to sulfur fertilizer, particularly on sandy soils. Corn and soybeans often do not respond to sulfur fertilizer, but yield responses can be substantial in cases where sulfur is deficient. Late season S supply is critical as sulfur uptake during seed fill increased with yield, while remobilization from vegetative tissue was relatively less than that of N (Gaspar et al., 2018). Some common conditions where S deficiency has been more prevalent include coarse-textured soils, low organic matter soils, side-slope landscape position, eroded soils, alfalfa crop, corn following alfalfa, and reduced- and no-till systems. In Kentucky, we have the sloping soils, eroded soils and no-tillage systems. Lack of soil mixing and cooler soils reduce mineralization, which slows release of S from organic materials. Loss of organic matter from eroded soils reduces potential available S from mineralization. Objectives: 1) Identify yield response in soybean to sulfur fertilizer applications 2) Conduct economic analyses on the value of these applications 3) Extend results to soybean growers through our Extension networks