Soil sampling procedures
Soil Sampling Procedures
The intention of the following information is to aid you in properly taking soil
samples under various conditions and for specific purposes. As it has been said
many times, "A soil test is only as accurate as the sample taken." Sampling Tools
Tools that may be used to take a sod sample include a spade or shovel, soil
sampling tube, or soil auger. Sample tubes or augers should either be stainless
steel or chrome plated.
When sampling various soils at different times of the season it is important to use
the proper equipment. A soil probe, either a hand tube or hydraulic probe, can be
used under most conditions. A small wooden rod may be helpful in removing the
soil core from the tube. The soil auger is especially useful when sampling frozen
ground or heavily compacted soil that a soil tube can't penetrate. If a spade is
used for sampling, dig a V-shaped hole to sample depth; then cut a thin slice of
soil from one side of the hole.
if using a pail to collect the soil, it should be plastic to avoid any contamination
from trace metals. For instance, soil will pick up zinc from a galvanized pail.
When sampling wet soils, vegetable oil or mineral oil may be used to lubricate
the probe to minimize soil pushing ahead of the probe. Sample Preparation
Mix cores or slices together in a clean plastic container and take enough
subsample to fill the special soil sample bag provided by the laboratory. There is
no need to process the sample further before shipment. At A & L Laboratories,
the sample received is dried, ground, and sieved by experienced technicians.
Send a separate bag if the Nematode Test or Residue Test is needed in addition
to the Basic Tests. Sample Size
A well-mixed composite from 10 to 20 random locations should be subsampled to
give 1 to 1Y2 cups of soil to be sent to the laboratory for analysis. Greater
amounts may be needed when physical properties of the soil (such as textural
classification, available moisture, nematodes or residues) are to be measured. Sample Area
Area to be included in a sample generally should be no more than forty acres.
Small acreages may be sampled when soil is not uniform throughout a field. A
soil map or crop response map can be of help in distinguishing areas.
Areas that differ in soil type, appearance, crop growth or in past treatment should
be sampled separately, provided this area can be treated separately.
Avoid small areas that are different such as dead furrows, corners of fields, end rows, and poorly drained areas. Stay at least fifty feet from barns, roads, lanes, or fencerows. The sample should be obtained from 10 to 20 locations within the areas as diagramed below.
When sampling problem areas, collect separate samples from both the poor area
and the good area to use as a comparison. it would be advisable to run a
complete test on a surface sample and a sample from a lower depth to provide
additional information. Include a description of the problem when samples are
submitted so that A & L agronomists may assist you in finding a solution.
If sampling an area with extreme variations, such as where land leveling has
occurred or erosion and deposition are severe, the field should be sampled on a
grid or incremental unit basis. Sampling Depth
When sampling, scrape away plant residue and sample to 6 inches; or if primary
tillage is deeper, sample to tillage depth. This is the depth that can be altered
with fertilizers or soil amendments. Eighty to ninety percent of the nutrients taken
up by the plant come from this tillage depth. Plants also obtain nutrients from a
lower depth. Subsoils can provide significant information regarding nitrate-
nitrogen and sulfur.
When sampling for nitrate-nitrogen, the most appropriate time for sampling is in
the spring or during the growing season. Since nitrate-nitrogen will move with the
waterfront, it can be leached deeper with winter and spring precipitation,
especially in sandy soils. Generally, when sampling for nitrate-nitrogen, A & L
recommends sampling at 1 foot increments down to 3 feet. It is suggested that
the depths be kept separate so that a more accurate assessment can be made
regarding soil fertility and soil physical conditions. Time to Sample?
Soil samples may be taken at any time during the year. However, it is generally
recommended to be consistent from year to year. If a particular field is sampled
in the spring, it should be sampled in the spring in following years. If this cannot
be done, seasonal variations should be expected and taken into account.
In addition, pH can vary during the growing season due to presence of soluble
salts, C02, organic matter decomposition, nutrient uptake and exchange, and
Nitrate-nitrogen and sulfate-sulfur are Teachable. Therefore seasonal variation
may occur in levels of these nutrients, depending on soil types, weather patterns,
and moisture levels.
Consistency in the time of year samples are taken can eliminate much of the
question of whether a variation does occur in a particular soil. A field history
should be established to help distinguish seasonal and sampling variation from
real fertility changes.
The best time to take soil samples is probably whenever it best fits into your time
schedule. However, there are several items to consider before sampling:
1. Allow ample time to receive results from the laboratory. 2. Sample when you will not be hurried - allow time for taking a
3. Sampling should be done in accordance with the grower's field
4. Taking both a soil sample and a plant sample during the growing season
may help distinguish nutrient uptake patterns from chemical, physical, or disease factors.
It is recommended that you sample fields every other year or every third year. In
the case of intensive cropping, manure or sludge applications, or sandy soils,
annual sampling is recommended to monitor the available nutrients or potentially
damaging salt accumulations. Specialized Sampling Sampling Reduced Tillage and No-Till
No-till and reduced tillage have different meanings to various people. When
referred to here, we mean any tillage that doesn't incorporate soil much more
than 3 inches. Remember, most disks and chisel plows, if run 6 inches deep, are
only incorporating to one-half that depth.
To get a representative soil sample under these conditions, it is best that soil
samples be taken from two depths. Take one from the surface 2 inches, and one
from the 0-6 inch depth. The 0-6 inch depth should be used for general fertilizer
recommendations. The 0-2 inch sample should be used to adjust the fertilizer
program placement and to provide for accurate herbicide programs. Generally at
the surface you will find higher fertility, higher organic matter content, and lower
pH, all of which affect the fertility and herbicide programs.
Usually a basic test is adequate for the 0-2 inch depth. However, a more
complete test should be run in some situations. Zinc deficiencies have been seen
under reduced tillage, even though the 0-6 inch sample showed adequate levels.
Shallow sampling revealed most zinc concentrated at the surface, positionally
unavailable to plant roots under dry conditions. Soluble salts could also
accumulate at the soil surface at higher concentrations than indicated by a 0-6
inch sample, causing stress to plants, particularly at early stages of growth. Sampling Ridge Till
When using ridge-till or ridging-up for flood irrigation, it is recommended that you
sample half-way down the ridge at a 45° angle to the ridge as shown below.
Sampling Center-Pivot Ground
Many who sample center-pivot ground include too large an area in their sample,
creating an excessive variation in results from year to year. Here are several
suggestions for best results:
1. Split the circle into thirds. This would limit the sample to about 45 acres.
Take about 15-20 cores from each of these thirds.
2. If time or expense is a limitation, take one sample from the hillsides and
3. If the circle is on flat land, sample two areas containing no more than 40
acres each. These two areas could be selected from extreme variations in the field. (For instance, sandy versus clay loams or one area that you know hasn't yielded as well as another area). Then either average the lab results from the two areas or else treat these areas of the field separately.
Whichever of these methods you use, keep the sample areas the same each
year. With these methods, inconsistencies in results from year to year will be
minimized and you will have a better field history file. Sampling Fields with Varying Terrain
If bottomland and hills both represent significant amounts of a field, take a
sample from each type of terrain. If either bottomland or hills represent just a
small area of the field, do not include these areas in your sample. Positive Placement of Fertilizers
Starters: When row-placed bands are used, sample between the rows. An
exception may be where the total fertilizer program is in a row-placed band. Here
you should probe about one-sixth of your total number of probes in or near the
row. Strip/Deep Placement:
Increase the number of cores per sample. Take two
cores near each other at a distance equal to one-half the band widths. Sample in
this manner at 12-15 locations to accumulate soil for a sample. Sampling for Herbicide Residue
Normal sampling procedures should be used with certain exceptions. The depth
of the soil sample depends on the herbicide in question and the soil. Most
herbicides do not move much in a fine textured (loam and clay) soil. Some
exceptions are Amiben, Banvel, 2,4-D and Tordon. On coarse textured (sandy)
sofis, all herbicides have more movement. Manufacturers are able to supply this
information for their own products.
Correct sampling depth is incorporation depth (i.e. 3") unless the herbicide is
quite teachable due to its chemical nature or the soil texture. If this is the case, a
6-7 inch depth is required. If moldboard plowing was performed prior to sampling
for residue, sample to plowing depth and inform the laboratory of sample depth
so that correct interpretation of residue effects may be made.
Each herbicide decomposes in the soil at its individual rate, but decomposition
slows when the soil cools, and stops when soil temperature drops below 620F.
This should be considered when planning sampling for herbicide residues.
Comparing Various Cropping Practices
Pasture / Turfgrass
In sampling pastures, follow normal sampling procedures. However, sample
depth should be 3-4 inches. Clean off the soil surface before probing and avoid
sampling near manure piles. Also avoid areas where livestock congregate or
heavily travel. Alfalfa / Clover
Sample soil prior to planting so that both pH and fertility corrections may be
made. A 0-8 inch sample is recommended unless problems exist. If alfalfa is no-
till planted, a 0-3 inch sample and a 3-8 inch sample are recommended. Orchard / Tree Farms
It is suggested that samples be taken from within the drip line of the tree at a 0-
18 inch depth. Micro-Irrigation
Be consistent by sampling at half the radius of the wetting zone of emitters.
Depth will depend on root zone. Soil and Plant Analysis for Problems
Soil and plant analysis during the growing season can be used to help diagnose
growth problems. Many plant abnormalities have causes that are more complex
than simple mineral deficiencies in the soil. These causes can often be
determined by an experienced agronomist using data from soil and plant
When sampling problem areas, make as many observations as possible of
conditions, which might contribute to the problem - soil compaction, drainage,
insects, disease, nematodes, chemical residue and other factors may contribute
in varying degrees to problems observed. Sampling for Nematodes
The best time to sample for most nematodes is while the crop is still growing so
that spots stunted by nematodes can be easily identified. In early spring,
significant populations have not yet developed except in warm climates where
preplant sampling can be very useful.
Ideally, one soil sample for nematodes should be taken for each five acres. If
sampling a problem area, sample toward the outside edge of the area for
greatest numbers. The largest populations of nematodes aren't likely to be found
where the severest crop symptoms are seen because these plants are no longer
able to support large nematode populations. It is advisable to take a comparison
sample from an unaffected area.
Take the samples from a depth of 3-18 inches in the root zone from 20-25 locations using a soil probe or spade. Mix the samples in a bucket and immediately place one to two pints of soil in a bag. Be sure to mark the bag "For nematode analysis." Do not let the soil dry out or get hot. Keep samples in shade or in an insulated cooler until the samples can be sent. Samples should be taken when the soil is moist, not when dry. The best method of collecting "root" samples is to spade up the plants and collect the tips of the roots and feeder roots; areas where greatest populations are found. In most cases, during the growing season, root samples are more useful than soil samples. However, testing both soil and root samples will give you the most useful information.
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