Impacts of Sulfur Fertilization On Yield, Grain Quality, And N Use Efficiency Of Wheat

Impacts of Sulfur Fertilization On Yield, Grain Quality, And N Use Efficiency Of Wheat – Year 2 Dave Van Sanford, Hanna Poffenbarger, John Grove and Carrie Knott Sulfur (S) is critical for plant health and completion of a normal life cycle. Historically, S has not been widely applied in crop production because crops were able to obtain enough from the soil and the atmosphere. However, the combination of higher yielding crops, cleaner air, and purer fertilizer products has led to increased frequency of S deficiency in many parts of the world. In Kentucky, a meta-analysis comprising 72 observations throughout the state between 2008 and 2012 found no significant yield response of corn or soybeans to S application, but a significant 2.6% average yield boost with S addition to wheat (yield increase ranged from 0 to 7%, Grove 2013). Although the yield gains in plot-scale trials have been modest, larger benefits may be observed on farmer fields where sloping and/or low organic matter zones exhibit greater S deficiency. Apart from the potential yield benefits from S fertilization, there may be quality benefits. Baking quality of wheat depends on quantity and quality of the protein. Both nitrogen (N) and S are components of plant protein and needed at a ratio of approximately 12:1 in wheat grain. If there is adequate N but too little S, the protein content of the grain could appear to be high because protein content is typically calculated using %N in the grain. However, that protein content value may simply reflect the accumulation of non- protein N, which has negative effects on baking quality. In addition, without adequate S, there will be fewer S-rich forms of protein, leading to a stronger dough that is more resistant to mixing and less extensible. A dough with high strength but low extensibility will not be able to rise against its own strength. We hypothesize that there may be sustainability benefits of S fertilization in wheat. An inadequate supply of S could lead to reduced plant growth and incomplete use of applied N. In contrast, plants not limited by S will grow more vigorously and will more thoroughly scavenge available N in the soil profile. A higher N use efficiency, calculated as the proportion of applied fertilizer N that is taken up, will lead to lower nitrate leaching and less environmental damage. In Year 1, we followed a two-pronged approach to understanding the potential benefits of S fertilization of wheat: 1) a literature review focusing on the linkage between grain N:S ratio and baking quality and the environmental conditions that lead to S deficiency in wheat and 2) a field study to determine the effects of S fertilization on yield, baking quality, and N use efficiency of several soft winter wheat varieties at two locations in Kentucky. The literature review and analysis are in progress. In the field study grown at Lexington and Princeton, the following varieties were used: Pembroke 2014 (early maturity, strong gluten), Pembroke 2021 (early maturity, intermediate gluten strength), Truman (late maturity, weak gluten), Pioneer 26R10 (mid maturity, unknown gluten strength), and Agrimax 454 (mid - late maturity, unknown gluten strength). There were three N levels (0, 90 and 120 lb/a) and these were combined with two S levels (0 and 30 lb/a). Leaf chlorophyll content at early heading showed significantly higher values in plots that received both N and S than in those that received N but no S at one of two locations. The yield data collected in these treatments will be used to determine effects of S fertilization on yield and N use efficiency. We will also determine the N and S content of the grain and measure dough characteristics including wet gluten content and loaf volume, an indicator of gluten strength. Grain samples will also be sent to the USDA-ARS Soft Wheat Quality Lab in Wooster, OH for a battery of milling and baking quality analyses.