Phosphorus fertility for wheat
The right P fertilizer rate should be determined by a well-calibrated soil test, such as the Mehlich 3, Bray P1, or Olson. Other tests may be good, but they are not calibrated for Kansas or Great Plains conditions, and don’t have the rate recommendations at a given test level developed. The rate needed for wheat is a function of soil test level. Wheat removes about 0.50 pounds P per bushel. But at low soil test levels, the recommended/required P rate for economic optimum yield is often 2-3 times the removal rate, especially when broadcast. At higher soil test levels, approaching the critical level, the soil is capable of supplying most of the P needed, and recommended fertilizer rates are often less than crop removal.
Essentially all of the normally available dry or liquid P sources, such as 11-52-0, 18-46-0, or 10-34-0 can be successfully used for wheat production, with little difference in performance seen between them.
One word of caution concerning fertilizer sources relates to ammonia and salt injury. While wheat is relatively tolerant to salt injury, and the narrow row spacing commonly used dilutes the amount of material in each row, as compared to corn or grain sorghum, each year a report will come in of fertilizer injury from fertilizer applied with the seed. In many cases this is the result of urea being added to the starter fertilizer mix. As a general rule, never apply urea fertilizers directly with the seed as this can result in ammonia injury. Also keep the salt load low. Ideally, the total amount of N plus K should be less than 30 pounds per acre in 7.5 inch rows.
In summary, P is a critical part of a wheat fertilizer program on soils with P soil test levels below 20 ppm. Applying the fertilizer at or before planting, and using some banded P, normally placed with the seed in today’s planting equipment, is the most efficient and profitable. The right P rate should be based on current soil tests.
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