Spectrum Agronomic Library

Soybean cyst nematodes (Heterodera glycines) have been an increasing problem for soybean producers over the past decade or more. H. glycines is the only cyst nematode known to attack soybeans in the U.S. Most of the major soybean producing areas of the U.S. now recognize that SCN is present in at least part of the area. SCN is and obligate parasite of higher plants, more than 1100 species of plants have been found to serve as hosts. Fortunately, most are weed and crop plants not commonly found in soybean fields or cropping rotations. Populations of the nematode increase rapidly under continuous soybeans, but decline drastically during the first year under non-host crops.

Severe infestations of SCN can have a devastating effect on yields. Yield losses can range from slight to as much as 90% depending upon the degree of infestation, soil fertility, cultivar susceptibility, environmental conditions, and race of the nematode. Root systems of heavily infected plants are drastically reduced, necrotic and practically devoid of Rhizobium nodules. In Iowa, susceptible varieties yielded about 40% less in infested fields than in non-infested fields. In Ohio on a fertile, dark colored soil, varieties resistant to SCN yielded over 50 bu/ac, whereas those susceptible to SCN yielded from 24-39 bu/ac (a yield loss of from 52% to 22%). Another study using aldicarb to control SCN found that high SCN populations may reduce yields by 30 bu/ac.

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With mother nature's constantly changing weather patterns in different areas of the country there comes concern during dry years of the build up of nitrate levels in plants (particularly in corn silage) and the effects that it can have on livestock when used as feed. This paper was written to help the reader become more aware of the different guidelines and university recommendations as well as university interpretations as far as how to handle the nitrates levels in corn silage. At Spectrum Analytic, we are not livestock nutritionists nor are we feed specialists, however we do have the capability to test for nutrients levels in feeds, forages and other plants. And in this process we are sometimes asked to help with interpretations of the results, and that is the purpose of this paper, to give the reader some basic knowledge about nitrate levels in drought stressed corn and some precautions to follow.

Excess Nitrates in Drought Stressed Corn

It is common to hear people discuss fertilizer recommendations in terms of crop removal, plus or minus soil test buildup as if they were somehow disconnected from each other. In fact, they are two aspects of the same subject. Most of us fall into the habit of thinking that we are fertilizing plants. Except for foliar fertilizer or tree trunk injection, we do not fertilize plants… we fertilize soil. Because of this, soil chemistry will determine how much of the applied nutrients the plants will be able to take up. If a soil is low in phosphorus (P) or potassium (K), it will tie-up or “fix” much of the applied fertilizer P and K (P₂O₅ and K₂O) into forms that are not available to the plants. This nutrient fixation is simply another way of saying that the soil is trying to build itself up in these nutrients… whether that is your intention or not. The soil is a reservoir for the nutrients that have been applied or generated by other means over the years. The nutrients that a plant gets in any one season are likely to be ones that have been in the soil for many years. Therefore you can think of fertilization as putting nutrients into one side of a reservoir while the plants are taking them out of another end. What happens inside of this nutrient reservoir is soil chemistry and microbiology. These processes, along with weather, determine how much access the plants have to the nutrients within the reservoir.

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