Managing phosphorus, nitrogen and potassium is fairly straightforward: Base your rates on soil test levels and crop removal and plants respond accordingly. But micronutrients also are essential for top yield, points out Farm Journal Field Agronomist Ken Ferrie—and deficiencies can show up during the growing season.
Knowing your soils can tell you where deficiencies are most likely to occur so you can promptly react.
One micronutrient getting a lot of attention recently is manganese. “Manganese deficiencies usually occur in soils with high organic matter content, such as muck or peat, dark-colored sands with pH levels above 5.8 and lake-bed and outwash soils with pH above 6.5,” says Darryl Warncke, Michigan State University soil fertility specialist. “Because it’s difficult to increase soil manganese levels, you can expect problems in the same areas every year for manganese-sensitive crops,” he adds. “Soybeans are one of the most sensitive.”
Symptoms of manganese deficiency include yellowing between the veins on the newer leaves of soybean plants and, in severe cases, stunting. “Early detection is critical in order to prevent yield loss caused by reduced photo-synthesis and nitrogen fixation,” Warncke says.
In studies, Farm Journal Associate Field Agronomist Missy Bauer found foliar applications of manganese boosted soybean yield from 0.9 bu. to 3.4 bu. per acre on heavy lake-bed soils in northwestern Ohio. “We know we have a manganese deficiency in those soils,” she says.
Response by soil type. In sandy soils, the yield response has been smaller, and sometimes nonexistent, Bauer says. “In muck and peat soils—which, in my area of south-central Michigan, tend to be spots within fields—it makes it difficult to measure the yield response,” she says. “But tissue tests show we have improved manganese uptake by the plants.”
In mineral soils in central Illinois, Ferrie says, he has “really struggled to get a yield response to treatments.
Tissue tests show I get manganese into the plants, but I don’t always get a yield response at harvest. I also have seen one replication of a trial respond to treatment, a second replication show no response and a third replication actually go backward.”
Deficiencies occur because manganese gets tied up, or fixed, in soil, Ferrie explains. So—except for rare situations involving certain very light soils—foliar treatments, rather than soil applications, are required.
“Foliar application of 1 lb. of actual manganese in 30 gal. of water per acre will alleviate deficiency symptoms and improve growth,” Warncke says. “If you apply a lower rate, regardless of the source, you often will need a second application. In one manganese-deficient field where a low rate was applied, the soybeans greened up only where there was spray overlap.
“With severe deficiency symptoms, apply 1½ lb. to 2 lb. of manganese per acre, in one spray or cumulative in multiple sprays, or make a second application two weeks after the first,” Warncke adds.
Bauer advises her clients to take a proactive approach. “We don’t like to see deficiency symptoms appear,” she says. “Think about your field’s history. If you have had manganese deficiencies in the past, you probably will have them again the next time the field rotates back to soybeans.
“Use soil and tissue tests, especially in newly acquired fields. Tissue testing tells us a lot about what is going on inside a plant. It can reveal a nutrient deficiency before we see visual symptoms. We probably should be doing more tissue testing, especially if we have nutrient issues in a field.”
Fix deficiencies. To correct deficiencies in growing plants, Warncke recommends farmers spray foliar applications of manganese sulfate. “Spray-grade manganese sulfate is soluble and provides greater crop safety than chelated forms of manganese at comparable rates,” he says. “If you apply glyphosate herbicide to a field, wait at least two days before applying the manganese.”
- September 2010