Peter Motavalli, Kelly Nelson,

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IMPROVED RECOMMENDATIONS FOR POTASSIUM
FERTILIZER MANAGEMENT IN MISSOURI SOILS
AFFECTED BY DROUGHT STRESS
Peter Motavalli, Kelly Nelson, Manjula Nathan
and Steve Norberg University of Missouri
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K DEFICIENCY
Increasing K deficiency in agronomic crops in
Missouri and other Midwestern states because of
several factors including

• The decrease in soil K availability due to
  drought conditions and soil compaction

• Reductions in applied K fertilizer and the
  frequency of soil testing by producers due to
  decreasing commodity prices

• Higher corn yields and increasing soybean acreage
  in rotation with corn has increased K fertilizer
  requirements

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OBJECTIVES

• To determine the relationship between soil K
  availability and soil moisture for growing
  soybeans in northern Missouri soils.
• To examine improvements in crop yield and other
  agronomic benefits of applying K fertilizer at
  different times during the growing season as part
  of a post-emergence weed management program.
• To evaluate the economic costs and benefits of
  post-emergence K applications in response to K
  deficiency.

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MATERIALS AND METHODS

• Two-year field trials at farm site near Greenley
  Agronomy Center in NE Missouri and field site at
  Hundley-Whaley Experimental Farm in NW Missouri.

• 4 rates of pre-plant K fertilizer (0, 125, 250
  and 500 lbs K/acre as potassium sulfate)
  broadcast-applied and 3 additional K rates (8, 16
  and 32 lbs K/acre) foliar-applied at 3 separate
  times (V4, R1-R2, and R3-R4 soybean growth
  stages).

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MATERIALS AND METHODS

• Will determine fate of applied fertilizer K by
  periodic sampling of soil and leaf tissue. Soil
  moisture will be determined at time of soil
  sampling. Potential salt injury by foliar
  application will be visually rated.

• Economic analysis will consist of determining the
  relative costs of K fertilizer addition versus
  the benefits in increased yields under varying
  weather conditions over the two growing seasons.

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INITIAL RESULTS - GREENLEY
Pre-plant K
Check
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INITIAL RESULTS - GREENLEY
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BENEFITS OF PROJECT

• Will increase our knowledge of factors affecting
  soil K availability for crops on soils in
  Missouri.

• Results will be used to develop improved K
  fertilizer management practices including the
  potential costbenefits of post-emergence foliar
  K applications.

• The information from this project will be
  incorporated into research and extension
  publications and workshops (e.g. Greenley Center
  and Hundley-Whaley Field Days).