You’ve tested your soil, scouted your crop and confirmed manganese problems by sending plant tissue samples to a laboratory. Now it’s time to fix those deficiency or toxicity issues and minimize their impact on yield.
“In some cases, broadcasting manganese, along with your other fertilizer, might increase soil test levels and prevent or correct deficiencies,” explains Farm Journal Field Agronomist Ken Ferrie. “However, in most situations, foliar applications, (possibly several applications) will be required.”
One place to broadcast manganese is on sandy, highly leachable soils. “Unless your sandy soil has a low pH, you can expect manganese problems,” Ferrie says. “Because of the risk of leaching on sandy soil, apply manganese fertilizer as close to plant uptake as possible—in the spring, along with potassium and phosphorus, for example.”
Ferrie recommends using the sulfate form of manganese because it is more readily available. On sandy soils, though, you might have to make an application every season, he adds.
In heavier soil, the problem usually involves getting plants to take up manganese from the soil before it becomes tied up and unavailable. “In such soils, broadcasting, in my experience, is pretty inefficient,” Ferrie says. “Doubling the amount of manganese in the soil won’t help. If you do choose to broadcast, apply the manganese as close to uptake by the plants as possible because anything not taken up will quickly become fixed and unavailable.”
In these soils, or any time you spot a manganese deficiency in growing crops, the best solution is foliar application. “But first, make sure manganese really is the problem,” Ferrie says. “Scout your crops, and send off samples for tissue testing. After you have become skilled at identifying visual symptoms, you might be able to eliminate tissue testing. In highly organic muck soils, where you know deficiencies will occur, apply manganese as soon as you see visual symptoms.”
When plants are small, the challenge with foliar application is to make sure the spray lands on plants, rather than on the soil where it will become tied up and unavailable. “If possible, use a directed spray or band the fertilizer over the row,” Ferrie advises. “Because manganese does not move inside the plant, you might have to make another application after new growth emerges. With severe deficiencies, especially with soybeans in mid-flower (the R2 or R3 reproductive stage), you might need to make several foliar applications.”
Soil-applying won’t help in alkaline soils, high-organic matter mucks or sands. Although foliar application is the best choice, you might be able to fix early deficiencies in those soils by adding manganese to your starter fertilizer, Ferrie notes. “In corn, you might also sidedress manganese, especially if you use a tool such as the Y-Drop,” he says. “It places fertilizer near the base of the corn plant, where it has a better chance to be carried inside by water through the mass flow process.”
In typical mineral soils, which is most soils, you are less likely to encounter manganese problems (although they might arise during drought or cool, wet growing conditions). “Clay loam soils, which are moderately drained and have water pH readings of 6.8 or 6.9, will have intermittent deficiencies,” Ferrie says. “In those soils, starter might not pay every year, and soil applications might get tied up. Scout those fields, and make foliar applications when needed. If possible, use variable-rate technology for your foliar application; you might only need to treat the areas prone to manganese deficiency.”
If you farm fields where organic matter content varies from 1% to 3%, you can help prevent manganese problems by varying your limestone rate. “If you apply a single rate across the whole field, you will apply too much lime on some soils and too little on others,” Ferrie says. “Overapplication wastes money, and underapplication will not maintain optimum pH levels. But, more important, if soil pH gets above 6.5, manganese and other nutrients will become less available. If it falls below 5.0, the soil might release excessive amount of manganese, which can be toxic to plants.”
In all situations, manganese sulfate is the most efficient form of manganese fertilizer, Ferrie says. “If you foliar-apply, use the sulfate form or chelated manganese. Manganese oxide fertilizer is cheaper, but it contains less available manganese.”
“Because manganese is not mobile inside the plant, time your fertilizer applications to match the early symptoms of manganese deficiency in your crop,” Ferrie adds. “That might not be the ideal time to simultaneously apply a herbicide or fungicide.”
Ferrie believes the unintentional overapplication of lime is causing manganese deficiencies in fields. Problems arise when a farmer’s nutrient management techniques have not kept pace with their implementation of new tillage practices.
“Aside from problem soils, a high percentage of the manganese problems I encounter as a consultant are, to some extent, manmade,” he says. “The problems result from how farmers incorporate lime.
“Years ago, the standard lime application rate was 3 tons to 4 tons of lime per acre followed by moldboard plowing or deep disk-ripping to incorporate. We applied 3 tons or 4 tons because we only tested our soil every five years, so pH showed major changes. We had to apply enough lime to correct past acidity and prevent acidity in the future.
“Today, many farmers use no-till, strip-till, vertical tillage or some other form of conservation tillage, which provides less incorporation of lime at a shallower depth,” Ferrie continues. “Because their application rates remain the same, they are incorporating large applications of limestone only a few inches deep. Three tons of lime per acre incorporated only 2" deep is the equivalent of 6 tons or 7 tons applied to the surface layer of the soil. That shifts the surface pH to alkaline and causes early season manganese deficiencies.”
When Ferrie discovers a new farm showing frequent early season manganese deficiencies, his first step is to test soil pH at 0" to 3" deep and 3" to 6" deep. If the surface pH readings are 6.8 to 7.2, that’s likely the cause of the manganese problems, he says. “The farmer might have to temporarily fix those problems by making foliar applications of manganese fertilizer. But long-term, the solution is to till to correct the stratification. After the farmer mixes lime uniformly throughout the top 6" of soil, he can return to no-till, strip-till or reduced tillage,” he adds.
“In the future, the farmer should test the soil every two years and apply 1 ton to 1½ tons of lime per acre every other year, rather than 3 tons to 5 tons every five years. This not only improves the availability of manganese and other micronutrients, but improves overall soil health by creating a better environment for soil microbes.”
Manganese toxicity is the opposite problem from manganese deficiency. “One of the primary causes of toxicity is acid soil,” Ferrie says. “If the soil pH is too low, manganese becomes highly available in the soil solution, which restricts plants’ ability to pick up calcium.
“Inside the plant, one of the main functions of calcium is to prevent manganese toxicity. It does that by forming calcium pectate, which blocks excessive amounts of manganese from entering the plant. Consequently, the visual symptoms of calcium deficiency are identical to the symptoms of manganese toxicity because that’s what it actually is,” he adds.
The solution to manganese toxicity is to lime the acid areas. “The lime must be tilled in to correct acidity throughout the soil profile,” Ferrie says. “That process might take six or seven years. After the acidity is corrected, a farmer can go to no-till, strip-till or reduced tillage. He should make frequent light applications of lime to hold pH in the optimum range.”
Toxicity also occurs in saturated or waterlogged soils. “In waterlogged soil, manganese toxicity is likely to be only one of many problems,” Ferrie says. “In that situation, there really is no way to correct manganese toxicity. The only solution is to improve drainage, if possible.”
Understand the role of pH and organic matter content in creating manganese issues; test your soil and learn to spot deficiency and toxicity symptoms, and you’ll keep manganese problems at bay, Ferrie concludes.