Rex Nielsen, agronomy technician at UNL's Panhandle Research and Extension Center, takes a five-foot soil sample to test for nitrogen in preparation for planting wheat. (IANR Photo by Gary Hergert)

August 10, 2007

Wheat harvest is only a few weeks behind us, but it's already time to start thinking about next year's fertilizer needs. The best way to determine your fertilizer requirements is with a soil test. Guidelines for taking a good soil sample are provided in these UNL publications Soil Sampling for Precision Agriculture, EC154, and Guidelines for Soil Sampling, G1740. (G1740 is expected to be available on the UNL Extension Publications Web site later this month.)

Soil samples for pH, phosphorus, potassium, and micronutrients should be done every three to five years as these values do not change rapidly even with fertilization. The topsoil sample should be taken from the zero to eight inch depth.

This year has produced rainfall extremes across Nebraska. West central to eastern Nebraska had above normal rainfall this spring and early summer while much of the Panhandle is still in drought conditions. Because soil nitrate is very mobile, sampling should occur before the crop is planted. Soil samples for nitrate should also be taken to at least a three-foot depth.

Fertilizer prices are also at historic highs with nitrogen and phosphorus costing nearly 50 cents a pound in most liquid and dry sources. The high cost of nitrogen and the mobility of nitrate highlight the importance of soil sampling to determine residual nitrate-N. Information from your soil tests plus fertilizer prices and expected selling price for your wheat are used in calculating nitrogen and phosphorus recommendations. (For more information see UNL NebGuides, Fertilizing Winter Wheat I: Nitrogen, Potassium, and Micronutrients (G1460) and Fertilizing Winter Wheat II: Phosphorus (G1461). A fertilizer recommendation spreadsheet (Excel) is available on the UNL Soil Fertility Home Page.

Even though fertilizer prices are high, the higher wheat price suggests that applying nitrogen is still profitable (Table 1).

Sources of Nitrogen for Wheat

All nitrogen fertilizer sources (urea (46-0-0); urea-ammonium nitrate (28 or 32-0-0); anhydrous ammonia (82-0-0)) are effective if applied properly. Anhydrous ammonia is still the most economical source of nitrogen, especially under conventional tillage, however, it is late to apply ammonia, especially in western Nebraska where moisture loss from application would be a major concern. Most ammonia is applied to fallow in late June and early July.

Fertilizing With Nitrogen for Grain Protein

Traditionally Nebraska has produced high quality wheat. This year weather problems in wheat growing states south of Nebraska caused much of that wheat to be low in protein. Consequently, many Nebraska producers received a protein premium this year. A grain protein level of 12-13% with an average yield indicates adequate nitrogen. University of Nebraska–Lincoln nitrogen fertilizer recommendations will produce grain protein of 12% or higher. If the goal is higher grain protein to obtain premium grain prices, about 20 pounds per acre of additional nitrogen will need to be topdressed in the spring to increase protein by 1%.

Gary W. Hergert
Extension Soils Specialist
Panhandle REC, Scottsbluff