Everyone is looking to the sky in Montana for crop-saving rain that just doesn't seem to be coming. But if heavy storms do sweep in, they bring them some downsides in the downpour.
Soil nutrients can be robbed by pounding rainwater, warns the Montana State University Extension, plunging nitrogen, sulfur and chloride levels to low levels. As a remedy, the researchers say added fertilizer may be needed to compensate.
Heavy spring rains lead to water-logged soils and cool temperatures that increase disease potential as well, the scientists note.
"To prevent yield losses and low protein, fertilizer can be added now, but only after verifying that the crop is nutrient deficient," advises Clain Jones, MSU soil fertility specialist in the Department of Land Resources and Environmental Sciences.
Visual identification of deficiencies can be seen in several different ways. Nitrogen deficiency commonly shows uniform yellowing form leaf tip backward, appearing on the oldest leaves first. Even legumes may be N deficient, he notes, if they are unable to fix their own nitrogen or take up sufficient N. Sulfur deficiency also causes uniform yellowing, but shows up on upper, younger leaves first.
Yellowing due to disease or lack of other nutrients is usually non-uniform, striped or spotty. Chloride can also leach, showing up as spots on some varieties of wheat.
To determine if N has been lost from a field, he recommends testing the soil for available ammonium and nitrate to at least three feet deep.
Ammonium testing can be omitted, however, if urea fertilizer was applied at least a month earlier because it will likely have converted to nitrate by now. If the soil test indicates insufficient N, re-apply nitrogen, says Jones, taking into account changes in yield potential.
If N deficiency is due to leaching below the reach of young roots or poor uptake because of water saturated soils, then patience may be best, he adds, noting that "yields can also be lost by being too patient."