Agricultural News
Soil Testing Being Used to Determine Sulfur Needs for Winter Canola
Thu, 04 Aug 2011 09:49:03 CDT
Sulfur (S) is considered the fourth most important plant nutrient. Its deficiency in canola has been reported in Canada and some parts of the United States due to:
-Environmental laws restricting sulfur dioxide emissions from industrial sources;
-The use of more concentrated fertilizers that do not contain sulfur impurities;
-Increases in yields resulting from genetic and technological advances;
-Decreases in pesticide and fungicides containing sulfur.
Some field studies have shown an increase in crop quality and yield following S fertilization. However, most of these studies were conducted in Canada and northeastern United States where deposition of S in rainfall is considerably lower than other parts of North America. The mineralization of soil S also occurs at a slower rate in the north due to low temperatures affecting the amount of plant-available inorganic sulfur supply. Nevertheless, producers are being encouraged to fertilize with sulfur regardless of soil test results and geographic locations, which may not be economically sound because many soils in our state are able to supply needed S despite the reduced input and increased demand.
A field trial was conducted recently in Perkins and Lahoma to find out if canola responses to S fertilization in Oklahoma. The treatments were designed to determine if two different types of sulfur fertilizers had an effect on yield and seed quality of two different canola cultivars. The two canola cultivars were hybrid HyClass 154W and open pollinated DKW 47-15. The two sulfur fertilizers used were ammonium sulfate and elemental sulfur. There were four rates of each sulfur source: 0, 10, 20, and 30 lb S/A. The study was repeated in 2 growing seasons: 2009-2010 and 2010-2011. We didn't find significant yield or quality increase due to S fertilization at either location. The results from 2009-2010 at Perkins are shown in Figure 1. Since the site at Perkins has a sandy texture, a response to increasing sulfur rates would be more evident and expected; however, due to adequate soil sulfur supply a significant response did not occur. Soils (0-18 inch) at both locations had over 60 lbs S per acre, which was adequate for the canola crop. Typically, the amount of S needed is about 1/10 of the nitrogen required. Therefore, a soil test should be taken to decide if S is really needed for our
field.
A typical soil test is taken at a depth of 0-6 inches; however, canola is capable of using sulfur at a much deeper depth. Therefore, a surface soil test (0-6") may not adequately serve as an accurate measurement and may underestimate soil S supply. A subsoil sulfate-sulfur (SO4-S) test (6-18") is needed to better assess soil S supply for canola production and to make more appropriate fertilizer decisions. Unnecessary increases in soil S does not lead to higher yields or higher oil content (as shown by our 2-year experiment) and may reduce seedling emergence if too much S is placed in the seed row. Extra sulfur may also add acidity to the soil and lower soil pH.
Our thanks to Malarie Barrett, Hailin Zhang, Mark Boyles and Josh Bushong for this article from the latest edition of Extension News Newsletter. For more information, contact hailin.zhang@okstate.edu
Click here to see Figure 1 and the data of elemental sulfure vs. ammonium sulfur
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