Making Sense of Soil Tests

URI Master Gardener Program

September 17, 2016

Dawn Pettinelli, UConn Soil Nutrient Analysis Labdawn.pettinelli@uconn.edu

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

SOIL SAMPLINGSampling Tools:

Soil probe best, augers OK, with spade take a uniform

slice

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

Photo by Nora Painten

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

That’s all folks!

THANKS!

QUESTIONS?