Manganese Deficiency Can Worsen with Spring N Applications on Small Grains

Richard Taylor, Extension Agronomist; rtaylor@udel.edu and Phillip Sylvester, Kent Co., Ag Agent; phillip@udel.edu

Over the years, with respect to soil pH and manganese (Mn) deficiency, we have found that barley seems to be if not the most sensitive then close to the most sensitive small grain. When soil pH approaches the mid 6 range where we would expect it to be optimum for corn and beans, we often see Mn deficiency symptoms on barley, especially in certain areas of the state where the native Mn levels are low. During late fall and winter, the symptoms can often be confused with winter injury, wind burn, or other problems. However, the confusion usually clears after nitrogen (N) fertilizer is applied in the spring. Unfortunately, clearing the confusion often means that partial or entire stands of barley are lost.

The impact of spring N can vary depending on the soil acidity profile. If the Mn deficiency is severe or if the deeper soil layers are higher in pH, the N applied can cause barley plants to quickly die or, as frequently described, the barley appears to go backwards in appearance. The N stimulates rapid growth and if Mn is not available either as a result of soil pH levels or just low native Mn levels in the soil, the plants suffer significant damage.

This has been the case in several fields in southwestern Kent County over the past couple of weeks. Of particular interest is a field shown in the photographs below. The field developed striping across it on 30-inch centers (Photos 1, 2, and 3). In some areas, plants between the “rows” died and disappeared (Photo 4) and in other areas plant growth was slower other than in the “rows”. As can be seen in the photos, the rows are very straight and on 30-inch centers. We think the pattern follows where starter fertilizer was applied next to the corn rows last year since the lines are very straight. Rather than residual nutrients, the effect is very likely due to the slight acidulation of the soil that surrounded the banded starter fertilizer. The slightly lower pH in these areas has increased Mn availability just enough so that the plants were healthy enough to survive until the field received foliar Mn about a week before the photographs below were taken. Between the ‘rows” where banded starter did not affect Mn availability, the plants were so stressed for Mn that the N application caused them to die.

This week we took additional soil samples to investigate whether we can detect the small pH differences expected and we will report on the results in a future issue of Weekly Crop Update.

A concern that the grower may have is whether the Mn deficiency will show up in double-cropped soybeans if they are planted after the barley. First, the foliar treatment on the barley will not have any effect on a future crop. Second, a soybean crop is subject to Mn deficiency but whether the soil Mn levels are low enough for symptoms to appear is still in question. Barley seems to be more sensitive than soybean so visual symptoms may not been seen in the soybean plants. However, there is a strong possibility that the soybean crop will suffer from what is often referred to as “hidden hunger’. This occurs when the soil Mn availability is not quite low enough to stimulate visual symptoms but is at the critical range where yield potential is lowered without visual symptoms appearing. Our recommendation is that either the grower should consider a broadcast application of Mn (usually for a broadcast application 30 lbs actual Mn is applied per acre) so that soil Mn levels are increased above the critical range or the grower should plan on a foliar Mn application around the fifth leaf stage (V-5) when enough leaf area is present to adsorb adequate Mn from a foliar application. One to two pounds of actual Mn is the suggested rate for a single application. This rate is suggested since application costs are more than the cost of the product and so a single application will be the preferred method.

Photo 1. Barley rows generated following renewed spring growth and nitrogen application showing effect of last year’s starter fertilizer.

Photo 2. Barley between corn rows was either severely Mn deficient or had died while barley on rows 30 inches apart grew vigorously.

Photo 3. Wide view of barley field with old corn rows showing vigorous barley growth.

Photo 4. Between the “rows” barley Mn deficiency symptoms following spring N application were severe.

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