BOZEMAN – With Montana’s wheat and barley harvest coming to a close, many of the state’s agricultural producers and their crop advisers are likely thinking about soil nutrient needs for the next winter wheat crop.
In Montana, nitrogen, phosphorus, potassium, and sometimes sulfur fertilizers, are required to grow healthy winter wheat. However, each fertilizer requires unique management techniques, according to Clain Jones, Montana State University soil fertility Extension specialist in the Department of Land Resources and Environmental Sciences in MSU’s College of Agriculture.
Jones encourages farmers to conduct annual soil tests to determine nutrient needs for the next growing season.
“Nitrogen is the nutrient needed in the greatest quantity, and typically provides the biggest yield boost,” Jones said. “MSU fertilizer guidelines are based on spring soil tests, and spring tests are especially important to calculate nitrogen rates to account for overwinter nitrogen gains or losses.”
Montana producers can make initial nitrogen rate decisions based on previous years’ grain protein levels, according to research from Rick Engel, associate professor in MSU’s Department of Land Resources and Environmental Sciences. Engel found that if grain protein from a field is historically below 12.5 percent for winter wheat, then yields have been limited by lack of nitrogen.
MSU’s Southern Agricultural Research Center with the Montana Agricultural Experiment Station, offers a fertilizer recommendation tool, found at http://www.sarc.montana.edu/php/soiltest/ and MSU Extension houses an economic nitrogen calculator found at http://www.msuextension.org/econtools/nitrogen/. Both tools can help calculate fertilizer requirements. These and more resources, including steps for hand-calculating fertilizer rates, are available at the MSU Soil Fertility Extension website found at http://landresources.montana.edu/soilfertility/index.html.
Jones suggests split nitrogen applications to reduce the risk of overwinter nitrogen loss and allow for rate adjustment in the spring according to growing conditions.
"If drought has lowered yield potential at that point, then the second application can be reduced or eliminated," he said.
Urea is the most common nitrogen source in Montana, according to Jones, who stresses that urea needs to be put into the ground whenever possible. Broadcast applications on cold or snow-covered ground are risky, he said, because MSU research has found the applications can lose up to about 40 percent of their nitrogen to the air when not protected with a "urease inhibitor."
Jones pointed out that if wheat has not responded to nitrogen, or protein is unexpectedly low, then sulfur may be deficient. Since the soil sulfur test is not a strong tool to determine sulfur requirements, the consideration to fertilize with sulfur depends on crop and field history.
"If the prior crop showed sulfur deficiency, then providing sulfur before or at seeding could be a wise investment," he said.
In contrast to nitrogen, phosphorus and potassium should be applied before or at seeding. Therefore, growers should do soil tests this fall or use soil test values from 2015 or 2016, since phosphorus and potassium soil levels are relatively stable.
Jones added that phosphorus is very important to winter wheat survival and yield, and is most effective when placed with seed or in bands (strips) adjacent to the seed to help produce strong plants going into winter.
Although phosphorus comes in different granular and liquid forms, the crop response is similar among them on a pound P2O5 per acre, or unit, basis. However, Jones said, phosphorus products with lower amounts of nitrogen are preferred because of fewer germination issues.
Potassium deficiency is rare for Montana crops, but levels should be monitored especially in sandy coarse-textured soils or where straw is removed, Jones said.
Potash is the primary potassium fertilizer source, which is best utilized when banded below the surface. Jones cautioned there are limits to the amount of phosphorus or potash that can be safely seed-placed. South Dakota State University and the International Plant Nutrition Institute have an online tool to calculate safe seed-placed rate at (http://www.ipni.net/article/IPNI-3268). Jones said potash is also effective when it is broadcast at or before seeding.
For more information, contact Clain Jones or visit http://landresources.montana.edu/soilfertility/index.html.
Clain Jones, MSU soil fertility Extension specialist, firstname.lastname@example.org or 994-6076