SOIL AND FERTILIZER K

1
Chapter

• SOIL AND FERTILIZER K

2
Soil Potassium

• Total K in soils averages about 40,000 lb/acre
• Soil potassium is present in four categorical
  forms
• occluded (within soil minerals such as feldspar,
  mica, etc), 98 of total
• fixed (trapped within the lattice of 21
  expanding clay minerals), 1 of total
• exchangeable. 1 of total (100-1000ppm)
• solution, 0.1 of total (1-10 ppm)

3
An equilibrium exists between each

• Soil K

Available K. Solution and exchangeable K
normally represent "available" K for plants
during a growing season
4
Available soil K

• Plant uptake is by diffusion (90) and mass flow
  (10)
• K is immobile in soil (on a scale of 1 to 100,
  with 100 being most mobile, NO3- is 99, K is 33,
  and HPO42- is 1)
• Factors affecting amount of available K to plants
• soil mineralogy and climate
• CEC
• clay and organic matter content
• K fixation and/or release
• wetting and drying
• freezing and thawing
• subsoil and rooting depth
• soil pH
• competing exchangeable ions

5
3 K cannot compete effectively for the more
tightly held Al3 and H
3 K can compete more effectively for Ca2 than
the more tightly held Al3 and H. It is easier
to increase exchangeable K by fertilizing a Ca
saturated soil than Al3 and H saturated
exchange complex.
6
Factors affecting plant uptake

• Any condition that affects root growth effects
  uptake (plant response) of available K, all other
  things being equal.
• compacted soil wet soil
• acid soil
• shallow soil
• herbicide injury
• K leaching (only a concern on permeable, low CEC
  soils)
• K Soil testing
• Exchangeable plus solution K (any extraction
  solution that will provide a strongly held
  cation, or a weakly held cation in high
  concentration)
• Must be correlated and calibrated
• calibrated on sufficiency basis like P,

7
Fertilizer K

• Muriate of potash (KCI), 0-0-62
• most common
• mined in Canada and New Mexico
• solid, 100 soluble
• Application methods are similar to that for P
  because it is relatively immobile in soil.
• exception for high yielding forage crops, where
  forage is removed (bermudagrass or alfalfa, or
  turf such as putting greens) if soil is sandy, K
  management should be more like that for N, where
  amount required is more closely related to yield.
• When both P and K are deficient, the yield loss
  will be a product of the sufficiencys for P
  and K. For example, if P is 80 sufficient and
  K is 70 sufficient, if neither deficiency is
  corrected by fertilizing, then the expected yield
  will be 80 X 70 (.80 X .70), or 56 (0.56 X
  potential yield).
• Salt Effect Salt Rate N K20Corn lt10 lbs
  Salt/ac with the seedWheat lt 30 lbs Salt/ac
  with the seed

8
Soil Testing

• Why soil test?
• We cannot sense (smell, taste, feel, see, or
  hear) the nutrient supplying capacity of the
  soil, because it is a chemical property of soils.
• Soils are inherently variable from one place to
  another in the landscape (spatial variability).
• Gross differences are often separated one from
  another and managed as individual units or
  fields. The size (acres) and shape of these
  units relative to the size of field equipment
  influences whether or not a particular unit will
  be managed separately. As agriculture has
  evolved to the use of larger and larger
  equipment, field size has increased and the
  separate management of small, differing areas has
  decreased. Consequently, landscape variability
  that used to exist among fields may now exist
  within a field.

9
(No Transcript)
10
(No Transcript)
11
K Management

• Nutrient availability for a soil changes with
  time in relation to management.
• Continued harvest removal of nutrients may result
  in deficiencies of those that are generally
  present in high concentrations in plants and for
  which the soil may have limited capacity to
  provide in plant-available form (e.g. N and K).
• Continued fertilizer input of some nutrients may
  result in a build-up of the nutrient to the
  point that a previous deficiency no longer exists
  (e.g. P fertilization of low yielding crops)

12
K Management

• Approaches to nutrient (fertilizer) management
• Ask the fertilizer dealer what are farmers using
  this year?
• Find out what the neighbor is using and fertilize
  like the neighbor
• Soil test one or two fields and fertilize the
  rest of the farm based upon the average
• Soil test each field, every year, until you have
  developed a confidence in your knowledge of what
  the field should test, knowing that soil test pH,
  P and K (immobile chemical properties) should not
  change much from year-to-year under normal
  practices.

13
Soil Testing

• How to make soil testing work/not work
• get a good, representative sample
• 15 randomly taken, 0-6 inch, cores from the area
  in question, placed in a plastic bucket.
• avoid small unusual areas (saline or sodic spots,
  gullies, eroded hill tops), sampling them
  separately later.
• mix contents of the bucket until all sample cores
  have been broken up and the soil is a homogeneous
  mixture, then fill the sample container.
• make sure sampling depth and time of year are
  similar if year-to-year comparisons are to be
  made.
• understand that results are an average of the 15
  spots randomly sampled in the field, and do not
  provide any information about the variation in
  the field.
• if field is highly variable, then the average
  made up of 15 cores each year will likely vary
  more than if the field was relatively uniform.

14
Soil Testing

• use a calibrated test for immobile nutrients,
  preplant (or preseason in the case of perennials)
  nitrate-N test or pre-sidedress nitrate test
  (corn), PSNT, for N in conjunction with yield
  goal .
• test results must be related to critical value,
  identifying soil test value above which crop
  response to added fertilizer is not expected.
• test results must be related to the amount of
  nutrient addition required to correct
  deficiencies when the soil test value is below
  the critical value.
• interpret the test results relative to the degree
  of adequacy or deficiency of the nutrient or
  parameter (lime or gypsum requirement) measured.
• develop at a fertilizer or soil amendment
  recommendation that is reasonable.
• evaluate soil test results over time.

15
Soil Testing

• Soil testing-fertilizer recommendation
  philosophies
• correct deficiency of current growing season
  (sufficiency)
• correct deficiency of current growing season,
  plus replace what crop removed (sufficiency
  maintenance)
• correct deficiency of current growing season,
  plus add extra to build-up soil test levels
  (sufficiency build up)
• Field test strips
• Planned treatment skips or double applications
  can be a good in the field soil test that will
  be influenced by the field environment and
  growing conditions
• wear-bar strips, like are used to visually show
  when it is time to replace worn tires on cars,
  can be useful, long-term field test stripsN
  Rich Strip for other nutrients