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Fluid Journal : Fluid Journal 2002-2004
Table 1. Selected soil properties from 0 to 12 inches depth at each site. Year Location Texture pH SO4-S (ppm) 2001 Cache clay loam 7.7 3.5 2001 Garfield sandy loam 7.8 3.0 2002 Weber sandy loam 7.5 3.8 2002 Garfield loam 7.0 6.3 demand exceeds soil supply capabilities. In the Western U.S., alfalfa yields in excess of 8 tons/A can be achieved. These high yields, coupled with a long history of production and use of clean (low S) irrigation waters in alfalfa production areas, are resulting in more incidences of S deficiency and need for S fertilizer. Effect of S on alfalfa has not been evaluated in Utah. Alfalfa yield varies throughout Utah, based on location, elevation, climate, and management system. Three to five cutting hay systems are common, depending on location in the State. In 1997-1998, symptoms of severe S deficiency were observed in irrigated alfalfa. A follow- up survey of soil samples submitted in 1998-1999 found more than 60 percent testing low in sulfate-S (SO4-S below 8 ppm). Several new S fertilizer sources are now available, including fluid potassium polysulfide and ammonium polysulfide. Our objective for this study was to compare the effects of different S sources and rates on irrigated alfalfa yield, as well as on plant tissue and soil test S concentrations. Responses S rate. Averaged over sources, sulfur increased yield by 0.34 to 0.61 ton/A (9 to 16 percent) above no S control (Figure 1). Generally, yield was maximized at the higher S rate of 100 lbs/A. S source. Yield responses were similar with all S fertilizer sources (Figure 2). Averaged over rates, yield with these S sources was 0.45 to 0.56 ton/A (8 to 19 percent) higher than the no S control. In one site-year (Garfield, 2001) yield was decreased when higher rates of S were supplied by potassium- magnesium sulfate or ammonium polysulfide, due apparently to salt damage and direct tissue burn. The effects were not seen at the other sites or years. Soil test sulfate-sulfur was in- creasedbyupto8to15ppmS(32to 60 lbs/A of S) after fertilization in all site-years. Based on this soil sampling, it appears that S fertilization effects would persist for at least two years after applications occur. Additional analyses are ongoing to relate soil test SO4-S to yield and tissue S concentrations. Specifics Soil properties. Sites were identi- fied with relatively clean irrigation water sources and low residual soil test S levels (Table 1). Each site was in established alfalfa with stand ages ranging from 2 to 3 years old. Fertilizers. Fluid potassium polysulfide (K-Sul, 23% S) and fluid ammonium polysulfide (N-Sul, 40% S) were applied at rates providing 25, 50, and 100 lbs/A of S. An untreated control was included. Potassium (KC1, 0-0-60) was applied to all treatments to balance K rates across the study at 300 lbs/A of K20. Application. Fluids were applied with an ATV-mounted sprayer with a 10-foot boom calibrated for each material. Both fluids were diluted 1:1 with water before applications. Soil samples were collected from all plots after first harvest at 0 to 12 and 12 to 24-inch depths and analyzed for SO4-S. Dr. Koenig is associate professor and extension soil scientist in the Plants, Soils, and Biometeorology Department, Utah State University, Mr. Heaton is Garfield County extension agent, and Mr. Barnhill is Weber County extension agent. 2 Fluid Journal Late Spring 2003
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