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

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

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