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Making Sense of Soil Tests
URI Master Gardener Program
September 17, 2016
Dawn Pettinelli, UConn Soil Nutrient Analysis [email protected]
Productivity
Profitability
Durability
Healthy environment
SYSTEM OBJECTIVES
Net profit
Resource use efficiencies
Return on investment
Water & air quality
Working conditions
Nutrient balance
Nutrient loss
Quality
Soil erosion
Biodiversity
Soil productivity
4R Nutrient Stewardship
Aesthetics
SOIL TESTING
From Nutrient Management Perspective:
1. Optimizing nutritional/ pH conditions for plant growth
2. Maximize return on fertilizer investment (don’t waste $)
3. Minimize negative environmental impacts (especially P & N)
SOIL TESTING
Consider your soil a storehouse for plant nutrients, a pantry of sorts. A soil test is a means to take a chemical inventory of the available nutrients in your soil. Can tell if you need more nutrients or if the shelves are overstocked.
WHAT IS SOIL TESTED FOR?
1. pH – measure of acidity/alkalinity – is limestone/sulfur
necessary – if so, how much?
2. Nutrient levels – how much N, P & K to add, if any
3. Lead Screening
SOIL TESTING
4 SEPARATE ACTIVITIES
1. Taking a Sample
2. Analyzing Sample
3. Interpreting Results
4. Making limestone & fertilizer recommendations
Most limiting factor
SOIL SAMPLING
How Many Samples? Depends on Sampling Area
• Soils that look different or on different parts of the landscape, ie. top of hill, poorly drained spot, etc. sampled separately
• Soils treated differently in terms of limestone &/or fertilizer application sampled separately
• Soils which should be similar but drastic differences in plant growth sampled separately
SOIL SAMPLING
Garden
Flo
wer
Bed
Hedge
Trees
Example of proper
sampling technique
for lawn. Individual
samples were
collected at each spot
marked with an X.
The samples were
then mixed together
to make a composite
sample.
House
low spot
x
x
x
x
x
xx
x
x
x
xx
x
10
Site
Sampling
depth
Morgan Soil
Test P
UMass
Recommended
P2O5
inches ppm lbs / 1000sf
Lake Placid 0-1 3.4 0.5 -1
0-2 1.2 1 - 2
0-6 0.8 2 - 3
Farmingdale 0-1 13 0
0-2 5 0.5 - 1
0-6 2 1 - 2
Soil test P values for three sampling depths from
two locations in New York
Soil test data adapted from Soldat et al. 2009, Slide courtesy of UMass
SOIL SAMPLING
• When To Sample? – Fall
is best but for
comparison purposes use
same time of year
• How often? Usually
every 3 years or to help
diagnose a problem
Murrell, 2009 Slide courtesy of UMass
SOIL ANALYSIS
Routine Soil Analysis
pH & Buffer pH (Lime req)
Extractable P, K, Ca & Mg
using Modified Morgan
Extractant
Extractable Micros + S
Estimated CEC & BS
Estimated Total Lead
Additional Tests
Organic Matter
Soluble Salts
Texture
Nitrate-N
WHERE’S THE NITROGEN?
Nitrogen is generally the most limiting nutrient for plant growth
The dynamic nature of the N cycle makes it difficult to test and manage
In humid environments, the value of routine soil testing to predict available N is limited by our ability to predict the weather. PSNT – for some crops
14
Drying soil samples
Addition of extraction
solution
Filtration of
extraction solution
Analysis of soil extract (ICP-OES)
SOIL ANALYSIS
SOIL ANALYSIS
Unavailable Available
A discrete fraction of available nutrients does not exist,…
Increasing availability
….rather, nutrient availability is more a continuum in soil based on specific conditions affecting solubility of different nutrient pools.
Soil test extractable
SOIL ANALYSISBecause so many factors influence quantity-intensity relationship,
soil testing can only provide an index of nutrient supplying capacity
of a soil.
SOIL MINERALS
ORGANIC
MATTER
EXCHANGEABLE
CATIONS ON SOIL
COLLOIDS
SOIL SOLUTION
Stored nutrients (quantity) Available nutrients (intensity)
SOIL TEST INTERPRETATION
1. A plant response to
addition of that nutrient
(correlation)
2. A soil test level at which
that response occurs
(calibration)
Extractable or available nutrient values have little
meaning unless they are shown to be related to both:
SOIL TEST INTERPRETATION
Below optimum Above optimumOptimum
Critical soil
test levelEnvironmental
critical level?
General concept of interpretation based on Sufficiency level of available nutrients
SOIL TEST INTERPRETATION
To develop these
correlations and
calibrations, regional
research is performed
with representative soils
ranging from deficient to
adequate for a particular
nutrient. Why best to use
local lab.
Magdoff et al., 1999. Soil Sci. Soc. Am. J. 63:999-1006
For example…
Relative yield of alfalfa (w/ or w/o P2O5) in 31 Vermont soils with a range in soil test P.
Critical soil test P = 4 ppm
Results from similar research conducted throughout New England over the last 60+ years provides our basis for interpretation.
SOIL TEST INTERPRETATION
PHOSPHORUS
• NECESSARY FOR PHOTOSYNTHESIS,
FLOWERING, FRUITING AND
MATURATION
• ENCOURAGES ROOT GROWTH
• COMPONENT OF DNA (Genetic material)
P important for plant growth, often deficient in native
NE soils but doing poor job managing this nutrient so
now P regulations in some states –CT, MA.
SOIL SATURATED WITH P –
WHAT’S THE PROBLEM?
• No plant growth problems from excess P
• Water quality problems with excess P
• Fresh water bodies can become eutrophic with additions of P
• Additions in parts per billion can cause problems
• Lost by runoff and leaching
Algae bloom in stream next to Amherst College athletic fields
When soil test P levels are optimum or greater, don’t apply more.
Zero P fertilizers are readily available.
P Law in Nutshell – no P to est. lawns unless soil test within last 2 years says so. Can use P when seeding, overseeding & sodding. Organics not exempt in CT.
23
PHOSPHORUS CONCERNS
EXAMPLE REPORT & INTERPRETATION
• Measuring extractable not total nutrients (index)
• Categories based on field experiments – want to be in OPTIMUM
• pH/buffer pH
• Estimated CEC
• % Base Saturation
• Micros & Sulfur
• Lead
• Recommendations
POTATO SCAB
• CORKY SCABS OR BROWN
SUNKEN SPOTS
• POTATOES DO NOT STORE
WELL THOUGH TASTE IS
NOT AFFECTED
• SOILBORNE
• AFFECTS POTATOES,
BEETS, CARROTS,
TURNIPS, PARSNIPS
• MAINTAIN A SOIL pH OF 5.2
OR BELOW
INTERVEINAL CHLOROSIS
INTERVEINAL CHLOROSIS IN RHODODENDRON CAUSED BY IRON DEFICIENCY. THIS MAY ALSO INDICATE OTHER MICRONUTRIENT DEFICIENCIES LIKE ZINC OR MANGANESE AS WELL AS DEFICIENCIES IN MACRO NUTRIENTS.
Photo by Carol Lambiase, MG
CHANGING SOIL pH
• Apply Sulfur
• Apply Acidic Salts of
Iron, Aluminum or
Ammonium
• Peat Moss
• Apply Limestones or Hydrated Lime
• Soluble Calcium Products
• Apply Woodashes
• Compost
To Lower pH: To Raise pH:
Amount of Lime Needed Depends Upon:
• Necessary Change in pH
• Chemical Composition of Liming Material
• Buffering Capacity of Soil
LEAD CONTAMINATION IS CAUSED BY:
• Lead-based Paints
• Leaded Gasoline
• Use of Lead Arsenate as a Pesticide
Pb
GARDENING PRACTICES THAT
REDUCE LEAD CONTAMINATION
• Locate Gardens Away From Old Painted Buildings and Heavily Traveled Roads
• Give Planting Preference to Fruiting Crops (tomatoes, peppers, squash, beans, corn, etc.)
• Adjust soil pH to 6.5
• Incorporate Organic Matter
• Maintain Phosphorous Fertility
• Keep Dust at a Minimum by Mulching
• Discard Outer Leaves
• Wash Thoroughly