Phosphorus fertility for wheat
It’s important that producers not overreact to lower crop prices for wheat by cutting back this fall on phosphate fertilizer, if it’s needed, for the wheat crop. Wheat is the most highly responsive crop we grow to P fertilizers. At low soil test levels, good profits can be made by using the right rate of P applied at the right time and in the right manner.
Soil testing is the key tool to determine if any crop, but especially wheat, will respond to added P fertilizers. In Kansas the Critical P Soil Test level (the soil test level below which a response to P fertilizer is likely) is 20 ppm using the Mehlich 3 P test. When soil test P levels (Bray P1 or Mehlich 3) are below 20 ppm, the likelihood of a wheat yield response to P is high. The lower the test level, the greater the probability of a response.
Considering the 4-R’s of fertilizer management -- Right Time, Right Place, Right Rate and Right Source -- P fertilizer timing and placement are especially critical in wheat production. Since wheat is a fall-planted crop and makes critical growth during colder weather, the best and most profitable timing for P fertilizers is at or before seeding. The first few weeks after emergence in the fall, are critical since P has major impacts on tillering and rooting of wheat. An early-season P deficiency can slow root and shoot growth and reduce tillering and plant development. A poorly developed plant is more susceptible to stresses in winter and spring. So applying P fertilizers at or before seeding is best.
Phosphorous fertilizer placement is also very important in wheat production. Cool soil temperatures during fall growth reduce the rate of P movement to developing wheat roots. By concentrating the P in a band near the seed, this problem can be overcome.
It doesn’t take much added P fertilizer, with the proper timing and placement, to have a big effect on early-season development and yields. Early work at K-State conducted in the 1930’s at low soil test levels, showed nearly twice the response from applying 20 pounds of P2O5 in the row with the seed compared to broadcasting the same amount. Those results are still valid today. Banding fertilizer near the seed is more efficient than broadcasting P, especially for crops like wheat which make critical growth during cool weather. Broadcasting P can improve early-season wheat growth, but broadcasting is less efficient and requires a higher rate to obtain a similar response, making it more expensive.
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