Fertilizer Source and Rate Affect Sulfur Uptake and Yield Response in Corn

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Fertilizer Source and Rate Affect Sulfur Uptake and Yield Response in Corn
T.E. Husa and D.A. Ruiz Diaz Summary With sulfur deficiencies being found throughout Kansas, the evaluation of sulfur fertilization and plant uptake are vital to optimize corn production. The objective of this study was to evaluate the effect of application rates of sulfur on yield and uptake in corn. Nutrient concentrations in corn biomass and grain were evaluated at the Kansas River Valley Experiment Field at Rossville, KS, in 2019. Five treatments were evaluated, including a control with no sulfur and no nitrogen (N), and four fertilizer treatments with 180 lb of nitrogen and four rates of sulfur fertilizer (0, 30, 50, and 200 lb S/a). The nitrogen source was urea and balanced for all treatments at 180 lb N/a. The sulfur-containing fertilizer applications were at the time of planting corn. Whole corn plant biomass and grain samples were taken at physiological maturity and analyzed for nitrogen and sulfur concentrations. Results for the study show that sulfur application rates have a significant yield response in corn, likely contributing to increased uptake of nitrogen. Moreover, high yielding environments increased total plant sulfur uptake and removal.

Introduction
Until recent years, sulfur is a nutrient that had often been overlooked. Increasing crop removals was due to higher yields, decreased atmospheric deposition, and a greater amount of crop residues have increased the likelihood of sulfur deficiency (Camberato and Casteel, 2017). Sulfur application is economically feasible in soils that have a severe sulfur deficiency, but not all fields respond to sulfur applications (Sawyer et al., 2011). Moreover, nitrogen application rates play a significant role in the response to sulfur application rates (Steinke et al., 2015). This study used Kansas State University's recommended rate for nitrogen for the Kansas River Valley Experiment Field and applied four different rates of sulfur.

Procedures
The Rossville field study was completed in September of 2019, initial soil samples were collected at the 0-6 in. soil layer and analyzed for various soil parameters (Table 1). The experiment was a randomized block design with four replications. Five treatments were evaluated, including a control (No N/ No S) and four rates of sulfur fertilizer (0, 30, 50, and 200 lb S/a), which will be called control, low, medium, and high, respectively. The fifth treatment solely utilized urea and served as the sulfur control treatment (Table  2). Sulfur sources include urea calcium sulfate (27% and 33%), and ammonium sulfate.
The nitrogen source for the S control was urea following Kansas State University's recommended nitrogen rate (180 lb N/a). Whole plant biomass and grain samples were collected at physiological maturity in the corn crop. Whole plant biomass samples were gathered, weighed, and dried at 140°F and then reweighed to attain dry matter content. Corn was harvested, and the yield was calculated and corrected to 15.5% moisture. After corn harvest, soil samples were collected from 0-24 in. depth. All the soil samples were dried at 106°F, and sulfur was measured by a monocalcium phosphate extraction. All statistical analyses were completed in SAS (v. 9.4 (SAS Inst. Inc., Cary, NC)) using the generalized linear mixed model (GLIMMIX) procedure for analysis of variance (ANOVA).

Results
Preliminary results for this study showed significant differences between sulfur fertilization rates for both nitrogen and sulfur plant total uptake (Figures 1 and 2). Whole plant sulfur uptake significantly increased when sulfur was applied. Increasing the rate of sulfur showed no significant difference between sulfur rates (Figure 1), suggesting a rate of 30 lb was sufficient for the corn crop. Increases in nitrogen uptake were seen when sulfur was applied (Figure 2). A substantial increase in nitrogen uptake is likely linked to keeping the balance of nitrogen to sulfur within the plant. Nitrogen uptake is indicative of increased yield and sulfur uptake, suggesting that higher-yielding environments will also have elevated levels of sulfur removal (Figure 3). Soil sulfate levels in the 0-24 in. soil profile post-harvest were only significantly different at the high sulfur rate (Figure 4). This is likely due to excess S applied related to corn total need. Preliminary results show that the highest sulfur application rate significantly increased yield compared to the urea-only application ( Figure 5). This suggests sulfur applied at the lowest rate may have not been sufficient for maximum yield. An increase in nitrogen provided significantly more yield gain over the control when compared to sulfur.      Figure 5. Corn yield response as affected by different rates of sulfur application. Letters represent significant differences between treatments at P < 0.05.