Fall wheat fertilization
Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
Planting time fertilization of wheat is very important for phosphorus and potassium nutrition of the crop. Having adequate phosphorus and potassium available for fall growth is important for root system development, winter survival and tillering of the plants in the spring. A 100 bushel per acre wheat crop removes 63 lbs P2O5 and 37 lbs K2O in the grain. And each ton of straw contains 13 lbs P2O5 and 23 lbs K2O. Therefore, a 100 bu/a wheat crop with two tons of straw per acre removed will remove 76 lbs P2O5 and 60 lbs K2O per acre. Be sure to soil test to determine the available level of phosphorus and potassium in the soil. Generally, no yield benefit occurs from applying phosphorus when the soil test value is above 25 ppm. Below this value, wheat yield may be improved by applying the recommended amount of phosphate.
The critical potassium soil test ranges from 85 ppm in sandy soils to 125 ppm in clay loam soils. Above these values yield benefit does not usually occur from K application. Below the critical value applying recommended amounts of potash may improve crop wheat. Even when soil levels of phosphorus and potassium are adequate, applying 25 lbs each of P2O5 and K2O per acre along with 25 lbs N/a will insure good fall root establishment and plant vigor. Studies in Ontario have indicated that application of phosphorus and potassium in bands near the seed at the time of seeding the wheat increased the potential for producing top yields as compared to broadcasting. When soil phosphorus and potassium levels are within 15 to 20 ppm above the critical level, it is good to apply maintenance amounts, equal to crop removal, of phosphorus and potassium if financial resources permit.
In an MSU study of the 2007 - 2008 growing period, various combinations of phosphorus, potassium, and sulfur broadcast just prior to seeding did not improve wheat grain yield over applying only nitrogen even though the soil potassium level was below the critical value. Including copper, manganese and zinc had no effect on yield.
Most of the nitrogen is usually applied for wheat in the spring prior to green up. Slow release nitrogen fertilizers now in the market place make it possible to apply more nitrogen in the fall prior to seeding with minimal concern for loss. In nitrogen studies conducted in 2005 through 2007 (harvest year) wheat yields with broadcast-incorporation of nitrogen as polymer coated urea (ESN) in the fall resulted in grain yields equal to those produced with urea or UAN applied at the same rates just prior to green up in the spring. However, applying the ESN prior to green up resulted in the best yields, six to eight bushels more than fall applied ESN or spring applied urea or UAN. Slow release nitrogen materials provide another option for nitrogen management in wheat.