Alabama Corn: Sulfur and Magnesium – Key Nutrients for Crop Development

We have been intensely tissue sampling corn over the last two years in north Alabama and the two nutrients that have been consistently deficient are sulfur (or there have been an imbalance in the nitrogen:sulfur ratio) and magnesium.

The early deficiency symptoms of both are expressed as interveinal chlorosis. The interveinal chlorosis progresses upwards as magnesium deficiency intensifies in corn. The older leaves may become reddish-purple and the tips and margins may die.

A tissue sample is needed to determine which nutrient is deficient as other nutrient deficiencies such as manganese and iron can cause interveinal chlorosis. Magnesium deficiency was determined to be the cause of interveinal chlorosis in the photo above after a tissue analysis.

The whole corn plant beginning about 1/2 inch above the ground should be sampled if there are less than four leaf collars (about 12 inch tall). The youngest collared leaf should be sampled on larger corn plants (leaf below the whorl prior to tasseling).

The ear leaf should be collected at tasseling before the silks turn brown. Fifteen to twenty-five corn plants or leaves depending on the corn’s growth stage should be collected per tissue sample. Tissue samples should be dry and shipped to the laboratory in paper bags (plastic bags are a no-no for tissue samples).

When large amounts of nitrogen are applied without also applying sulfur, a sulfur deficiency can be induced in corn and other crops by an imbalance of the nitrogen:sulfur ratio. A nitrogen:sulfur ratio of 10:1 to 15:1 should be maintained for optimum yields.

It is advisable that sulfur be an integral part of a grower’s fertility program. Products such as 28-0-0-5 are an excellent source of both nitrogen and sulfur. Conditions that impede root growth, such as cold, damp weather during germination/early growth or sidewall compact in the root zone, can also contribute to nutrient deficiencies.

We got some very encouraging results from our 2017 replicated on-farm corn trials at Henderson Farms in Limestone County (irrigated) and Greg Key’s farm (dryland) in Cullman County with an application of K-Mag. K-Mag, some-times referred to as Sul-Po-Mag, is 22% sulfur, 22% potassium and 11% magnesium.

We got a 19 bushel per acre yield increase over the farmer’s fertility program at the dryland trial and a 16 bushel per acre yield increase over the farmer’s fertility program at the irrigated trial. We also got, more importantly, a net increase of $43.28 per acre in the dryland trial and $31.94 per acre in the irrigated trial.

This was due mainly to the additional sulfur and magnesium as when we added the additional 44 pounds per acre of potassium in the dryland trial we did get an 8 bushel per acre yield increase but only a third of additional profit ($43.28 versus $15.80).

When we added an additional 200 pounds per acre of 0-0-60 (a total of 120 additional pounds of potash) in the irrigated trial, we got a slight increase in yield (four pounds per acre) but a loss of $25.87 over the farmer’s fertility program (a loss of $67.81 per acre compared to the addition of the K-Mag).

We are conducting these trials again in 2018 as the 2017 trials may have been an anomaly. We would like to express our sincere appreciation to Greg Key and Henderson Farms for allowing us to perform these on-farm trials and The Alabama Wheat and Feed Grains Committee for funding the trials.

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