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Title: P and K Fixation by Missouri Soils

Principal Investigators: Peter Scharf, Randy Miles, and Manjula Nathan Departments of Agronomy and Soil and Atmospheric Sciences, University of Missouri

Objectives for 2001:

  • Conduct the laboratory incubation to measure P and K fixation of forty different Missouri soils.
  • Evaluate whether P and K fixation differ widely between north and south Missouri soils.
  • Evaluate whether other soil measurements, such as extractable aluminum, can be used to predict P or K fixation by different soils.
  • Use results to plan appropriate field experiments that would lead to improved P and K recommendations; these might be region-specific, or based on an additional lab test such as extractable aluminum.

Methods:

  • Obtain 20 soil samples representative of each region (north Missouri + Mississippi River valley is one region, south Missouri is the other), and for which the soil series is known.
  • All samples will be surface soils, 0 to 6 inch depth. This is the soil zone to which fertilizer is applied and where fixation of fertilizer nutrients may be an important process.
  • Mix small samples (200 grams) of each soil thoroughly with either:
    • 10 mg of P solution (this should raise Bray 1 soil test P by about 25 lb/acre)
    • 10 mg of K solution (this should raise soil test K by about 20 lb/acre)
    • distilled water
    • evenness of nutrient-soil mixing is the reason for using solutions
  • All treatments will be replicated three times. Because this study is exploratory, surveying a range of Missouri soils, we felt that it was best to allocate our resources to looking at more soils and use a minimum number of replications.
  • Incubate in the lab, keeping the soil moist, and measure the amount of extractable P (Bray 1 method) and K (ammonium acetate method) after six months, along with soil pH.
  • Measure extractable aluminum in the extracts also; Vermont research has shown that this can be a useful predictor of P fixation.
  • Make soil clay mineralogy measurements (X-ray diffraction, selective chemical dissolution).
  • Use statistical analysis of covariance to see whether soil region, soil aluminum, soil pH, or soil mineralogy can be useful in predicting how much P & K are fixed by different soils. Within a soil region, look for patterns that suggest what types of soils should be represented in future field experiments.

Soils collected for P & K fixation study
CountySoil
LinnLagonda
BooneMexico
MississippiCommerce silty clay loam
GentryGrundy Silt Loam
SalineHaynie silt loam
LafayetteHigginsville silt loam, eroded
StoddardLilbourn(2)fine sandy loam
StoddardLoring silt loam
MonroeMexico silt loam
MonroePutnam- Pasture
KnoxPutnam silt loam
New MadridSharkey clay
RaySharpsburg silt loam-9% slope, eroded
ScottCommerce silty clay loam
DeKalbGrundy silt loam, 1 to 5 % slopes
RayLeta silty clay
StoddardLilbourn fine sandy loam
StoddardLoring silt loam, eroded
LafayetteMarshall silt loam
MonroeMexico silt loam
MontgomeryMexico silt loam
PemiscotPortageville Clay
MonroePutnam
StoddardSharkey silty clay loam
LewisWesterville silt loam
LawrenceCreldon silt loam
VernonBarco loam
VernonBarden Silt Loam-Soybean
VernonBarden Silt Loam
ChristianClarksville very cherty silt loam
PolkGoss gravelly silt loam
VernonOsage silty clay
LacledeViraton silt loam
VernonBarco loam
VernonBarden Silt Loam
WrightCedargap cherty silt loam
CassHaig silt loam
HenryHartwell silt loam, 2 to 4 % slopes
LawrenceHuntington silt loam
LawrenceKeeno cherty silt loam
BatesKenoma silt loam, 1 to 4 % slopes
BartonParsons silt loam , 0 - 1 % slopes

Results for 2001:

  • Forty-two soils have been collected from all over the state, representing many major agricultural soil types (see map and table).
  • Soils have been dried and ground, and initial soil tests have been run.
  • Soils were analyzed for water content at field capacity, so that we would know how much water to add to each soil during the incubation procedure.
  • Incubation study was initiated in July, 2001.
  • Soil clay mineral analyses are in process.

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