Is Sulfur Limiting Soybean Yield In New York?
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In New York, soybean (Glycine max (L.) Merr.) yields have not yet reached their genetic potential. Reduced ambient sulfur (S) deposition, combined with increased crop yields over time and a change from S-containing nitrogen (N) and phosphorus (P) fertilizers to urea, monoammonium phosphate (MAP) and diammonium phosphate (DAP) which do not contain S, has contributed to increased occurrence of S deficiencies in forage and grain crop such as alfalfa (Medicago sativa L.) and corn (Zea mays L.) in recent years. Given a reduction in S deposition from an estimated 10 kg SO4-S in 1991 to 3 kg SO4- S ha-1 currently, combined with an increase in yield over time from 2,690 kg ha-1 to greater than 4,708 kg ha-1, farmers are now asking the question if S could be limiting soybean production in New York. Sulfur is especially important for legumes like soybeans as it plays a critical role in N2 fixation. Plants use S to regulate photosynthesis and build proteins and enzymes. In soybean plants there are two key amino acids that contain S, cysteine and methionine. Insufficient S supply can result in a reduction of both yield and crude protein (CP) content in soybeans, impacting crop production and grain quality. Thus, it is important to ensure sufficient S is available, especially given the increasing yield potential of soybeans. Chapter 1 summarizes the literature on S needs for soybeans. In particular, we identify historical trends in soybean production versus decline in atmospheric S deposition, discuss factors affecting soybean supply of S for growth, yield and nutritional value, and present studies on tools used for S management. Modern soybean varieties now produce more biomass (photosynthetic activity) with improved nutritional value thanks to a combination of breeding and agronomic management improvements. This translates into higher S uptake per cropland unit. Reduced S supply by deposition combined with greater S removal in harvest explains the increasing incidence of S crop deficiencies and, thus, the need for tools to assist in S management decisions. Tissue testing can be used to assess S deficiencies of plants. Soil S testing can identify potential for crop response to the application of S fertilizer earlier in the season but additional work is required to establish critical values for soybean soil testing methods. Field S balances can also be viewed as a management method for end-of-season assessment. Chapter 2 presents the result of on-farm S response trials, conducted to understand the impact of S fertilization on soybean grain yield, crude protein (CP), S content, N:S ratio, and crop S balances. On-farm, replicated, trials were performed in thirteen locations in western New York comparing two S sources (CaSO4 and (NH4)2SO4) versus a no-S control. The lack of response to S addition in tissue analyzes conducted at early bloom and full maturity were consistent with results of soybean grain yields and CP levels, and in N:S ratios and did not suggest an S limitation. The negative partial S balances of the control treatments (crop removal – S supply by S deposition) showed a significant contribution of soil S to total crop supply. Soil organic matter (SOM) measured by the loss-on-ignition, however, was not a good soil S supply predictor. Therefore, critical soil test S levels could not be determined given none of the thirteen trials showed a crop response to the addition of S. We conclude that S at this time does not limit yield potential but continued monitoring is important as partial balances indicate that S may become deficient over time.
crude protein; deficiency indicators; soybean; sulfur; yield
Ketterings, Quirine M.
Cherney, Jerry; Overton, Thomas R.
M.S., Animal Science
Master of Science
dissertation or thesis