Nitrogen Fertilization of Dryland Wheat in Southwest Kansas

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Nitrogen Fertilization of Dryland Wheat in Southwest Kansas Charles A. Norwood and George M. Herron Garden City Branch Experiment Station
Fertilization of dryland winter wheat was studied for many years by agronomists at the Garden City Experiment Station. These studies were conducted in several counties and were discontinued when it was felt that adequate data were available. The results of these older studies indicated that wheat seldom responded toN on silt loam soils but did respond on sandy soils. In the mid 1970s renewed interest in nitrogen fertilization developed because of the implementation of Improved cultural practices and newer varieties of wheat. Therefore, studies were from 1977-1980 with the objective of determining if the improved practices and varieties would result in responses to N.
Studies were conducted In Lane, Stevens, Kearny, Grant, and Hodgeman counties of southwest Kansas.
The tests were on silt loam soils in all counties except Stevens, which was on loamy fine sand , and Grant in 1979, which was on sandy loam. All fields had been fallowed the previous year. Nitrate measurements were determined on soil samples taken prior to fertilization in each year. Ammonium nitrate at rates of 0, 25, and 50 lbs N per acre was topdressed in March of each year.

Results
Soil test values are presented in Table 1, along with a "yes or no" indication as to whether or not an increase in yield due to fertilization was obtained. Yield data are presented in Table 2. Generally a response to N occurred if the soil test value for nitrates in the surface two feet of soil was less than 50 pounds (about 10 parts per million}. Two locations, Kearny in 1978 and western Hodgeman in 1979, did not respond although the values were 31 and 41 pounds respectively. Conversely, there was a response in Lane County in 1980, even though the soil test value was 89.
protein contents are given in Table 3. A low protein content is frequently regarded as an indication of inadequate N fertility. However, yield levels and climatic conditions also influence protein content. High or low yield levels can dilute or concentrate protein content. This may have been the case in eastern Hodgeman County in 1979, when unusually favorable climatic conditions resulted in high yields, yet protein contents were relatively low. Both yield and protein increased due to N. In contrast, yields were relatively low in Grant County in 1977, yet protein levels were high; neither yield nor protein responded to N. Protein responses occur more readily than yield responses, however. While only 11 of the 2llocations showed a yield response, 18 locations showed a protein response.
With the exception of the site in Stevens County, a sandy location that responded each year, yield responses seemed to depend on where the sites were located in southwest Kansas. A response in Kearny County occurred only in 1979, a year in which climatic conditions were highly favorable for wheat. A response in Grant County also occurred in 1979, on a sandy loam soil where such a response is likely. Further east, in Lane County, responses occurred in. three of four years. Three of the six sites in Hodgeman County responded. Thus, yield responses appear to be more likely in the higher rainfall, eastern area of southwest Kansas. Increases in protein content, however, seemed to be independent of the location.

Conclusions
Increases in wheat yield due to nitrogen fertilizer are more likely in the eastern counties of southwest Kansas. Occasional responses may occur in the western counties, however. A response to nitrogen will notre-suit every year, regardless of the location, unless the soil is sandy and moisture adequate. Increases in protein content are likely, and occur independently of the location or soil type. Rates of N between 25 and 50 pounds will usually be adequate for maximurr grain yield.
For more than a decade wheat yields have increased because of improvements in cultural practices and varieties. The higher yields result in additional depletion of soil nitrogen reserves. Thus, increased se of N fertilizer in the future is likely. Soil tests for N dre helpful in determining fertilizer requirements.