Transcript Principal of soil testing - WVU Ext

Principles of Soil and
Plant Testing
December 2009
Eugenia Pena-Yewtukhiw
and Jeff Skousen
West Virginia University
Techniques to Assess
Field Nutrient Status
Deficiency Symptoms of Plants
Plant Analysis
Soil Testing
PLANT ANALYSIS
Visual Deficiency Symptoms
Use only as supplement; to monitor the crop
Deficiency = nutrient stress has affected yield
Visual symptoms may be caused by more than
one nutrient (or ..)
Deficiency of one nutrient may be related to
excess of another
Difficult (sometimes) to distinguish among
deficiency symptoms in the field
Objectives of
Plant Tissue Analysis
To help identify/confirm deficiency symptoms
and to determine nutrient shortages before
they appear in the plant
To identify potential problems in fields with
inadequate nutrient management history
To aid in determining the effect of fertility
management on nutrient acquired by crop
To study the relationship between nutrient
status of the plant and crop performance
Plant Tissue Analysis
Nutrient status at the time of sampling
Easy to perform
Deficiency may have already caused yield loss –
TOO LATE!
The crop may not respond to added nutrient
The crop may be too large for nutrient application
Climate conditions may be unfavorable for nutrient
application
Plant Tissue Analysis
Sample at peak periods of nutrient demand
Compare plants from
deficient areas and normal
areas
Genetic variability among plants, so composite
samples taken from 10 to 15 plants to give a
single sample
New Developments
In Plant Analysis
Corn Stalk Nitrate Test
An end-of-season test that can be used at the
end of the season to verify whether the N
management program supplied sufficient N for
optimum yields, or it can be used to compare
alternative N management practices.
The test cannot be used to fine-tune the N
management program during the season of
growth.
New Developments
In Plant Analysis
Sampling For The Corn Stalk Nitrate Test:
Samples taken within 3-week period beginning
at grain ‘black layer’ formation. Typically, this is
about 2 weeks after silage harvest, but about 2
weeks before grain harvest
Take 15 stalks per field/area being monitored.
Take stalks undamaged by insects, etc.
Cut 8-inch portion of stalk, starting 6 inches
above ground – remove outer stalk sheath.
Handout:
Corn Stalk Nitrate Test
by Lloyd Murdock and Greg Schwab.
University of Kentucky
Techniques to Assess
Field Nutrient Status
Deficiency Symptoms of Plants
Plant Analysis
Soil Testing
SOIL TESTING
Objectives of soil testing
a) To give an index of nutrient availability
b) To predict the probability of obtaining a
profitable response to lime and fertilizers
c) To provide a basis for recommendations
regarding the amount of lime and fertilizers
to apply
d) To evaluate the fertility status of soils on a
geographic area basis
Components of Soil Testing
o
Sampling
o
Analyze the quantity of plant available nutrients in
the soil (based on extraction)
o
Interpret soil test results
o
Estimate the additional nutrients required by the
crop
Soil Sampling
Critical aspect of soil testing
The weakest link in the soil testing process
Less than 10 g of soil are used in the
laboratory to ‘represent’ a field that may weigh
more than 2 million lbs per acre-furrow-slice
Use soil testing guidelines for collecting
‘representative’ soil samples
Where to Sample?
Capability Classes
USDA NRCS
Soil Sampling
Define “field”, by size or other management
unit
Collect separate samples from areas that are
to be managed separately
Collect separate samples from areas with
different:
o
soil types?
o
past cropping/management histories
o
production potential
Soil Sampling Techniques
Field average sampling
Grid sampling
 point sampling
Soil Variability
Nutrient
Range
ppm
Average
ppm
Mode
ppm
Nitrate-N
2-24
11
8
P
0-104
15
9
K
127-598
276
155
Sulfate-S
7-9440
480
10
Other Soil Sampling
Considerations
Depth of sampling



tillage depth
0-2 and 2-8 inch for no-tillage
0-2 for pastures
Influence of Tillage on
Stratification of Soil Test P
Depth
inches
0-3
Plow
ppm
37
Chisel
ppm
85
No-Till
ppm
90
3-6
47
35
27
6-9
30
15
18
9-12
8
8
8
Chemical Analysis
Simple, rapid, accurate ‘index’ of soil nutrient
availability – inversely related to plant response to
additional nutrient(s) applied as fertilizer(s)
Laboratory test procedures vary among states
Analytical results generated by different
procedures are not interchangeable
(Mehlich I  Mehlich III)
Amounts extracted depend upon extracting
solution chemistry, extracting solution strength,
soil to extracting solution ratio, shaking time, and
filtering procedures
Common Extracting
Solutions
Mehlich-I (double acid)
Mehlich-III (ammonium fluoride & acetic acid)
Olson’s extractant
Morgan’s extractant
Bray’s extractants (Bray I and Bray II)
Approaches to Soil Test
Interpretation
Maintenance approach
Cation saturation ratio approach
Sufficiency level approach
Maintenance Approach
Rapid build up of the soil test to high soil test
levels
Annual application of amounts removed by a
crop
Some fertilizer applied, regardless of soil test
If a soil’s delivery capacity for a given nutrient is
adequate for optimum yields, then this approach
causes over-fertilization
Cation Saturation Ratio
Approach attempts to create an “ideal” ratio,
balance, among nutrients, especially K, Ca and Mg
Base saturation 80%
Cation ratio: 65% Ca, 10% Mg, 5% K, 20% (H + Al)
Ca/Mg = 6.5
Ca/K = 13
Mg/K = 2
Problems With The Cation
Ratio Saturation Approach
No consistent relationship between crop
response and cation ratio
Ideal ratios likely vary among soils
Sufficiency Level Approach
Based on a soil test taken every two or
three years, add nutrients according to
the results of those regular soil tests.
If soil test indicates available nutrient(s)
levels are ‘sufficient’, no lime or
fertilizer(s) recommended
New Developments In Soil
Testing
A new soil test for nitrogen:
Pre-Sidedress Nitrate Test
(PSNT) for Corn
(and only for corn)
New Developments In
Soil Testing
The basis for this new soil test for N is to take soil
samples just before side-dressing --- after the early
spring wet period but before the period of corn’s
major N demand --- and determine the nitrate-N
already in the soil at that time. The results are used
to make side-dress N rate recommendations.
Works best on soils with prior manure or killed
legume history.
Samples taken between rows, after crop emergence,
to a depth of 12 inches (see handout).
Handout:
Pre-Sidedress Soil
Nitrate Test for Corn
by Douglas Beegle, Richard Fox, Gregory
Roth, and William Piekielek.
Penn State University
EXAMPLES
Soil Testing
Laboratory
Analysis Results
Conclusions
Time of sampling is vital for plant tissue
analysis.
Soil testing is the easiest approach to
maintaining soil fertility
Conclusions
Soil test values depend upon soil test
methods
Recommended nutrient application
rates vary with soil test results and the
interpretation of those results