Soybean response to starter fertilizer containing sulfur
There is widespread concern about potential sulfur (S) deficiencies in corn and soybeans in the North Central region. 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.
Another important source of S is the soil organic matter. When organic matter decomposes, S is released as a sulfate ion into the soil solution. In Michigan, sulfur deficiencies are most likely to occur on coarse-textured soils with low organic matter. Other factors that may contribute to the need for supplemental S include increased crop removal rates in intensive cropping systems and lack of S impurities in major fertilizer sources.
In 2013, an on-farm research project was conducted in Perry, Mich., where Access starter fertilizer containing 17 percent S was banded 2x2 at planting at the rate of 2 quarts per acre and compared with untreated. The plots were 12 rows wide at 30-inch row spacing. The two treatments were randomized and replicated four times. The trial was planted on May 26, 2013. The soil was a Boyer sandy loam with a pH of 6.2, Cation Exchange Capacity (CEC) of 5.1 meq/100g and soil organic matter 1.5 percent. Syngenta S29-V2 Brand Avicta complete soybean bean variety was used and the planting population was 135,000 seeds per acre. The previous crop was corn and seed was treated with inoculant prior to planting. Uppermost fully developed trifoliate leaf prior to flowering was sampled July 15 for nutrient analysis and soybeans were harvested Oct. 12.
In addition to S, Access also contains micronutrients iron (Fe) 0.25 percent, manganese (Mn) 0.05 percent and zinc (Zn) 0.05 percent.
click image to zoom The yield difference between the Access and untreated treatments was not statistically significant (p<0.05, Table 1). Sulfur and micronutrient levels in the foliar tissue also were not significantly different (p<0.05 percent). For soybeans, the S sufficiency range is between 0.20 to 0.40 percent. Both treatments were within this range.
This site was a mineral soil with low CEC and low organic matter where the likelihood of S deficiency was high. However, the expected responses from S containing starter fertilizer on soybean yield and sulfur uptake were not evident in 2013. A point of noticeable interest was the inability to achieve a substantial increase in S uptake in the Access treated plots over the untreated. Perhaps testing a rate higher than 2 quarts per acre in the starter or other S-containing fertilizer sources should be considered.
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