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Step-by-Step Sulfur

March 8, 2014
By: Darrell Smith, Farm Journal Conservation and Machinery Editor
Photo for sulfur management story
Pale green color in the top of the plant or the whorl of the plant, along with stunted growth, indicates sulfur deficiency, explains Farm Journal Field Agronomist Ken Ferrie.  
 
 

Application methods, placement and timing depend on soil conditions in each field

Your crops will never run short of sulfur, a crucial building block of healthy plants, and you won’t waste fertilizer dollars if you follow The Fertilizer Institute’s 4Rs of Nutrient Stewardship. The 4Rs include applying the right fertilizer source at the right rate at the right time in the right place.

Of course, you won’t need to apply sulfur fertilizer if your soil already is supplying a sufficient amount and if it’s being taken up by plants, says Farm Journal Field Agronomist Ken Ferrie. Sulfur management should be based on soil testing and plant tissue analysis.

First, scout your corn fields for symptoms of sulfur deficiency. "Visual symptoms tell you to be suspicious," Ferrie says. "They include pale color, stunted growth and delayed maturity. Sulfur deficiency symptoms are similar to those for nitrogen deficiency.

"The difference is that a nitrogen deficiency shows up in the older leaves at the bottom of the plant. Sulfur deficiency shows up in new growth—the top of the plant or the whorl of corn plants. That’s because plants can move nitrogen from the old growth to the new growth, but sulfur, unlike nitrogen, is not mobile."

Be alert for sulfur deficiency on fields that have been heavily manured. "Soil phosphorus levels above 90 ppm [parts per million], often resulting from high rates of livestock manure, inhibit sulfur uptake by plants," Ferrie says.

Tissue and soil tests. If you suspect a sulfur deficiency, confirm your observations with tissue analysis and soil tests. Have plant tissue analyzed several times during the season—early, mid-season and late. To fertilize effectively, you need to know when plants are running short of sulfur, and then time applications accordingly.

Test your soil to see if there’s a sufficient supply. "Look for high, medium or low sulfur levels," Ferrie says. "Keep in mind that different laboratories use different methods to extract sulfur and have different ways of reporting the results. One lab might consider a reading of 8 ppm to 12 ppm to be medium, while another lab’s idea of medium might be 25 ppm. Don’t compare results from one laboratory to those from another unless you know both labs used the same extraction process. You can avoid confusion by staying with the same laboratory for all of your soil testing."

If your soil test reveals adequate levels of sulfur but tissue tests show a deficiency, the sulfur in the soil is not getting into the plants. There could be several causes.

"Soil compaction is the first thing to look for," Ferrie says. "Other possibilities include saturated soils and cold soils, both of which impact microbial activity, and severe root pruning by insects such as rootworms. In those situations, the solutions include reduced tillage, improved drainage or pest management to enable plants to utilize the sulfur in the soil."

Soil acidity (discussed below) can also impede sulfur uptake.

The right product (sulfate versus elemental sulfur) and the correct timing, placement and rate will vary depending on the situation. "With sulfur, there’s no one-size-fits-all method of treatment," Ferrie says.

5

Sulfur is not mobile in the plant, so early uptake is vital to prevent stunting and shortened internodes. 


Pay the carbon penalty. If a sulfur deficiency shows up shortly after emergence, the cause might be the carbon penalty. The carbon penalty occurs when soil sulfur levels are adequate, but there is an abundant supply of old crop residue, as with continuous corn. With all that food available, microbial populations explode. Because the microbes use sulfur, they temporarily immobilize the supply in the soil. That sulfur becomes available again later, after the microbes die and decompose, but the plants experience a deficiency through six or seven growth stages.

Sulfur deficiencies early in the growing season are especially troublesome. "Plants need sulfur throughout the vegetative growth stages. Since sulfur is not mobile in the plant, early uptake is crucial. A deficiency at that time will cause stunting and shortened internodes. So be aggressive about correcting early-season deficiencies," Ferrie says.

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FEATURED IN: Farm Journal - March 2014

 
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