Soil Sampling and Analysis

Brian Freking

LeFlore County Extension Educator, AG

Soil Sampling

• Goals:

1. To collect a soil sample that is representative of a field

or portion of a field

2. To obtain info. about a field and use that info. to make

management decisions

• Nutrient management

• Herbicides

• Crops

• Others

http://websoilsurvey.nrcs.usda.gov/app/WebSoilSurvey.aspx S17 T6N R25E

How to take a soil sample 1. Determine where/how you will sample

Sampling a Field 1. Random

Sampling a Field

Zone Method

Loam Formerly 2 fields

now all 1 field

Sand

Muck

Never limed

Limed 5 years ago

3 zones 2 zones 2 zones

The Wrong Way to Sample

If this were a 15 acre field and all areas were

sampled and combine into one composite

sample, what would the results tell you?

Gentle slope

Well drained

Flat

Poorly drained

Steep slope

Well drained

Soil Sampling: How often? • In general, each field should be sampled once

every 3 years

– Follow NRCS 590 Standards

• Which state that fields must be sampled in less than 20

acres increments.

• Fields may be sampled up to 40 acre increments IF the 40

acres is all one soil type and has been farmed the same for

10 years.

How to take a soil sample

2. Gather equipment

• Buckets

• Probes, augers

How to take a soil sample

3. Sampling depth (typically 6”)

• Depth of tillage is a good guide

• Be consistent with which ever depth you choose

4. Place the 20 cores into a bucket & mix thoroughly

5. Place in sample box

• Fill out info. on box & paperwork

What does a soil test indicate?

• pH and lime recommendations

• Organic matter

• Cation Exchange Capacity

• Phosphorus and Potassium

– Nutrient recommendations based on crop

• Mg and Ca

• Micro nutrients upon request

• Nitrogen

– Recommendation, but not generally based on tests • Specific tests may be available but may require specific

sampling timing and procedures.

pH value

defines

relative

acidity or

basicity

9.0

8.0

7.0

6.0

5.0

4.0 Very strong

Strong

Medium

Moderate

Slight

Slight

Medium

Strong

Basi

city

A

cid

ity

Neutrality

Mo

st p

rod

uct

ive

soil

s

Soil acidity and Oklahoma rainfall

Usually

acidic

Usually not

acidic

A Soil’s pH Is Affected

by Several Factors:

• Decomposition of organic matter

• Parent material

• Precipitation

• Native vegetation

• Crops grown

• Soil depth

• Nitrogen

fertilization

• Flooding

Soil pH in LeFlore County pH>6.5

9%pH5.5-6.5

34%

pH5.0-5.5

45%

pH<5.0

17%

Crop Yield Ca Mg

Estimated Calcium & Magnesium

Removed by Some Common Crops

Alfalfa 8 t (hay) 175 40

Bermudagrass 8 t (hay) 60 24

Corn 150 bu (grain) 2 14

Cotton 1,000 lb (lint) 2 3

Soybeans 50 bu (grain) 7 15

Tall Fescue 4 t (hay) 41 15

lb removed

Fertilization, particularly N,

speeds the rate that

acidity develops

Potatoes like

acid soils

Alfalfa likes

neutral soils

Apply lime

well ahead of planting

Relative Neutralizing Values of

Some Common Liming Materials

Relative

Liming neutralizing

material value, %

Calcium carbonate 100

Dolomitic lime 95-108

Calcitic lime 85-100

Baked oyster shells 80-90

Marl 50-90

Burned lime 150-175

Burned oyster shells 90-110

Hydrated lime 120-135

Basic slag 50-70

Wood ashes 40-80

Gypsum None

By-products Variable

Relative

Liming neutralizing

material value, %

Lime required depends on

soil pH and CEC.

The more clay and

organic matter, the higher

the buffering capacity.

Lime Requirement

• Raise soil pH to 6.8 for all crops except for

continuous wheat

• Raise soil pH to 5.5 for continuous wheat

• Amount recommended is ECCE lime

• In practice, pH 5.7 is okay for most grasses

• It takes time for soil pH to increase

Soil Acidity Affects Plant Growth

• The performance of soil-applied herbicides can

be adversely affected

• Reduced activity of symbiotic N fixing bacteria

• Clay soils high in acidity are less highly

aggregated

• Availability of nutrients such as P, K and Mo

is reduced

• Tendency for K to leach is increased

Placement

Another important factor

determining the

effectiveness of lime