A Basic Guide To Soil Sampling

Soil testing is the single most important guide to the profitable use of fertilizer and lime. It is in the best interest of farmers, lawn care professionals, landscapers, gardeners, fertilizer suppliers, and consultants to promote the use of soil testing for several reasons.

• Grow Higher Crop Yields
• Produce Higher Quality Crops And Ornamentals
• Use Fertilizer Dollars More Efficiently

The Goal:

The purpose of soil testing is to identify the soil fertility that the plants or crop, in a given area will experience. The soil area and volume could be a large field, a small garden, or simply the root zone of a single tree or shrub. The most difficult step in soil testing is accurately representing the desired area of soil. A laboratory cannot improve the accuracy of a sample that does not represent the area.
In most soils, it takes more than one year to make significant changes to the soil test levels. As the soil improves with better fertility programs, subsequent crops or plant growth should show increasing rates of improvement. Soils are formed over thousands of years, and are not easily changed in a short time.
The Method:

You should plan how the field is to be sampled before you begin. You should plan how you will divide the field into sampling areas…then always use the same areas in the future. A soil map, available at the county Soil Conservation Service office will often be helpful. Some factors that might cause you to sub-divide the field into separate sampling areas are…
• The size of the field
• Different soil types
• Different topography
• Different past usage (previous crops, livestock confinement, fertility practices, etc.).
• Fertilizer application capabilities
• Different past crop performance
Soil test levels in any soil area will vary both laterally and vertically. This, plus the intended use of the field, dictates how the field or area of land should be sampled (see example in Fig. 1).
. 1 There is no single best way to sample all fields, you must evaluate the land and its’ intended use, and then use your best judgment to get samples that will accurately represent the field.
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A Few Universal Basics

1. Soil samples can be taken with a professional soil probe, or simply using a shovel, spade, or garden trowel (see fig. 2).
2. Each sample should be composed of from 10 to 15 cores.
3. As you take cores of soil, put them into the plastic bucket. Mix the soil thoroughly in the bucket (galvanized buckets will contaminate the sample with zinc), breaking up all cores. Then, fill the soil bag to the green line (about 1 cup of soil). Discard any extra soil.

4. The cores should be taken in a random pattern that is uniform across the area being sampled (grid sampling may require a specific pattern).
5. Each sample should represent 10 acres, or less, per sample(grid samples will represent from 2.5 to 5 acres per sample).
6. Normally for most agronomic crops and conditions, each sample core should be taken to a depth of 7″ in tilled fields. Special conditions such as no-till, orchards, turf, and others are discussed in the following sections.
Tip: Permanently mark your soil probe at the depths that you expect to pull samples. This will help you maintain constant depth. A probe with a welded foot pedal at the correct depth is also helpful.
7. Complete the information on the soil bag while you are in the field! Assign each sample bag an ID consisting of up to 12 letters and/or numbers that will let you identify it later. Record the sample ID on a field map (hand drawn if necessary), as well as the pattern and locations in the field that the samples were taken. This will enable you, or others to take the next samples in the same locations.
8. Enter all necessary information on the soil sample information form, and check to see that it agrees with the soil bags it accompanies. These forms can be obtained on our web-site at www.spectrumanalytic.com
The Tools:

• Soil sample bags, soil information forms, and shipping boxes obtained from Spectrum Analytic, Inc.
• A chrome plated or stainless steel soil probe or auger. Shovels and spades may be used (see Fig. 2), but they are inefficient.
• A plastic bucketto mix the “cores” of soil in. Do not use equipment made of galvanized metal. The soil sample will be contaminated by the zinc in the galvanized metal.
• A pen or marker with water-proof ink for labeling the soil bags.
• We recommend that you take a clipboard or notebook and, if possible, field maps to record how the field was sampled.
• If you plan to be sampling large acreage’s each year, you may want to invest in larger equipment to improve efficiency such as ATV’s, hydraulic soil samplers, etc.
Sending Samples to the Lab:

Pack the soil sample bags into the boxes available from our lab, or other suitable shipping containers. If you have less than a full box of sample containers, it would be best to include some additional packing to keep the soil sample containers from sliding loose in the box. Be sure to include a completed Soil Sample Information form in the boxes. If you do not use our soil sample information form, be sure to list your full name, address, and telephone. Also, include a list of samples in each box with your sample number included. Finally, tell us which tests we are to conduct, and whether or not you want fertilizer recommendations. If you want fertilizer recommendations, you must tell us the crop and yield goal, or plant species if ornamentals are being grown. While our soil sample bags are extremely water resistant, and we can accurately analyze “mud”, it will be difficult for you to pull representative samples from a muddy field.
Tip: We strongly recommend that you send samples by UPS, or a similarly efficient method. Most of our customers use UPS, and we often get 2 day service from anywhere in the country. Third class mail can take many days, and may cost more for heavier boxes.
Tip: When you have several boxes to send, put a shipping label on each box, then tape several boxes together…you’ll get a cheaper shipping rate from most carriers! Check with your carrier for any weight limits that may apply.
Sample Turnaround Time:

We will typically complete a soil analysis on the following work day after we receive the sample. We often work on Saturdays and sometimes Sundays during the peak of the busy fall season. The printed report forms will be returned by first-class mail. Total sample turn-around time will typically range from 6 to 10 days, depending on how you ship samples to the lab. Sample results can also be accessed at www.spectrumanalytic.com, or by e-mail. Contact Spectrum Analytic to set up this service.
Special Sampling Situations:

1. No-till

Research indicates that it is advisable to take 2 separate soil samples. A 2 inch deep sample to evaluate surface pH, and a normal 7 inch deep sample for nutrient information. Since most fertilizer N is applied to the surface of no-till soils, they tend to develop a much more acid layer in the top 2 inches (see Table 1). This can lead to poor performance of herbicides. No-till practices cause significant nutrient stratification in the soil, which can complicate sampling and interpretation. However, fertilizer recommendations are still best accomplished with a normal 7 inch deep sample.
2. Fields with Banded/Starter Fertilizer

As you read this, you may decide that neither option is practical. If so, the best approach is to either avoid any known fertilizer bands entirely, or to take at least 15 cores per sample, pulled at random across the area to be sampled. This approach is not perfect, so you may see some unusual results at times. If you want to use a more “scientific” method, read on. These methods are applicable to both “starter fertilizer” bands, and those from pre-plant “field banding”.
The key to getting statistically correct representative samples is to take the correct number of cores of soil from outside a band, in relation to each core taken in the band. The following systems are the best methods that we know to determine the ratio of “in-band” to “out-of band” soil cores.
• Known Band Location: In this case, use the following formula to determine how many cores to take, and how many of them should be outside of the band.
o S = 8 x [band spacing (inches)/12]
o Where S equals the number of cores taken outside of the band for each core taken in the band.
• B. Unknown Band Location: In this case, some version of random sampling is the only choice. Research has shown that the statistically best method is as follows. Take the first core in a sampling area at random. Each subsequent core should be pulled at one-half the band spacing away from the first, while walking at a 90 degree angle to the direction that the bands were applied. Again, pull 15 cores for each sample bag, as described above, for maximum accuracy.
3. Soil Nitrogen Sampling

Since nitrate-N (NO3-N) is the dominate form of N in most soils, most calibration data and interpretation is based on it (even though the crop can use both forms of N). This work assumes a typical background level of ammonium N (NH4-N). This presents several conditions that must be taken into account to get the best use out of soil N testing.
• NO3-N is mobile in the soil, so a deep sample must be taken. In the humid parts of the country (most of the country) the research is calibrated to a 1 ft deep sample. In the dry Great Plains it is calibrated to a 2 ft deep sample. At the time of this writing, there is no calibration for a sample taken at a more shallow depth.
• The assumed background level of NH4-N can be dramatically wrong if the grower is using a nitrification inhibitor, or slow release form of N. In these cases, you should request that both forms of N be tested for. In any event a significant amount of NH4-N can convert to NO3-N while the soil is in the bag causing your results to be higher than the crop will experience in the field. This will lead to a lower than needed recommendation for additional N. We recommend that each soil N sample be either be shipped “next-day” delivery, or force-dried before shipping it to the lab. The actual temperature that is needed is about 100 to 110 degrees F, but microwaving the sample on the high setting until dry may be the easiest method. Microwaving will over-heat the sample, thus causing it to be unsuitable for other tests, but this is OK because the other tests aren’t appropriate for a 12″ to 24″ sample anyway.
4. Tree Crops – Orchards, Christmas Trees, Nurseries

Tree crops must be sampled much differently than row crops or forages. Also, with tree crops, plant analysis is more important that soil testing, and should be done every year! There are several opinions on the best way to sample tree crops, and they are somewhat dependent on the planting pattern of the trees. We prefer the following; however it requires additional care on your part…
A. Organization: Divide the field into blocks of trees of the same species, the same general age, and the same general soil conditions (topography, color, etc.). Within each block, select 5 trees that are typical of the general condition of that block (size, health, yield, etc.). These trees will be used as indicator trees for the rest of the block. They will be intensively sampled (soil and foliage) and monitored as a guide to the treatment of the entire block. These indicator trees should be permanently marked or tagged so that you can come back to them each year for re-sampling.
B. Soil Sampling: From each indicator tree in a block, pull 3 to 4 cores from the drip-line of the tree (the outside perimeter of the maximum foliage diameter). The resulting 15 to 20 cores will make up a single soil sample. Mix the cores well and take about a cup of this soil for the sample and send that to the lab. Fertilize the entire block according to this sample.
C. Plant Sampling: With tree crops of any type, it is important to use annual plant analysis in addition to periodic soil samples to determine your fertility programs. This is due to several reasons, such as a trees’ extensive root system, nutrient storage by some woody plants, and slow internal nutrient transport by large trees. It sometimes requires more than one year for woody perennial plants give the maximum response to a change in fertilizer programs. Take this year’s leaves/needle along with a less frequent soil sample to develop and refine the fertility program for the next season. You can also use leaf/needle analysis to determine the need for foliar sprays. The proper tissue to sample is… Fruit trees: youngest fully matured leaves on current years twig growth, 30+ leaves…Conifers: the entire current years growing tip after it has hardened, 20 to 30 tips
5. Lawns and Turf

Sample depth should be 4 inches, and should not include accumulated surface organic materials such as thatch, or the blades of grass. It would be desirable to not include the grass roots either, but this may be nearly impossible to avoid. Sample handling procedures at Spectrum Analytic will remove most of the roots and larger pieces of non-soil material. The pattern of taking the cores is similar to that used in sampling crop fields (random and scattered), and avoiding unusual areas, unless the unusual areas are of interest.
6. Nematode Sampling

We offer analysis for soybean cyst nematodes. The following instructions apply to all nematode samples. However, soybean cyst samples do not require that the nematodes be kept alive in the sample during transit to the lab. If you sample a field for nematodes other than soybean cyst nematodes, you will need to take special steps to insure that the soil moisture and temperature are correct at all times for the nematodes survival.
Nematodes do not normally infest a field in a uniform pattern. You will normally see an oval to irregular pattern of stunted plants (possibly dead ones in the center of the damaged area). It is best to take a nematode sample in the growing crop, so you are sure to sample the infected area of the field. In a growing crop, take from 10 to 20 cores from the perimeter of the affected area (see Fig. 4) to make a sample. You should avoid the interior of a dead area because the nematodes will have either left the area, or died due to lack of a host plant. You want to sample the area of heavily infected plants, so you will also want to take the cores from within the root zone, where the nematodes are. The depth of sampling should be from 6 to 8 inches in all soil except sandy soil, where your cores should be 10 to 12 inches deep.

Make a 1-2 pint composite sample from the cores, place it in a regular soil sample bag and ship it to the lab. We do not have a special nematode information form at this time, so simply write on the regular form that a particular sample is to be tested for soybean cyst nematodes.
7. Subsoil Samples

As a general rule, you gain most of the needed soil fertility information from proper topsoil samples; however there are times when a sub-soil sample can provide valuable information. Roots must thrive in the entire natural rooting volume of the soil for top yields. Most cultivated plants, except some turf varieties and a few ornamentals, extend their root systems into the subsoil, so problems in the sub-soil can limit yields. This is especially true of deep rooted perennials, annuals with tap roots, and trees. The subsoil can inhibit root growth in several ways such as undesirable pH, deficient or toxic levels of certain elements, severe compaction, excess moisture, and possibly other reasons. In these cases, the roots will be restricted to the topsoil for their entire needs. This can lead to nutrient or water stress and lower yields. Of course, correcting sub-soil problems can be very difficult, so identifying the cause of a problem does not necessarily mean that there is a practical solution.
Subsoil samples should be taken separately from the topsoil sample. To do this, first take the appropriate topsoil sample and place it into a plastic bucket. Then insert the soil probe back into the same hole and take another core to the new depth. Place these cores into another plastic bucket. When you label the bags of soil, and the soil information forms, record the depth of each sample for future reference. The lab analysis will be the same for each of the two samples, and we do not have a special recommendation program for subsoil samples, but the subsoil results can be used to modify the recommendations from the topsoil sample on a case-by-case basis.
Common Questions About Soil Sampling:

1. Q: When is the best time to take soil samples?
A: Anytime that you need them! In the fall, just after harvest is usually the preferred time in farming because the fields are empty and sampling is quicker, and the crop has had all season to pull nutrients out of the soil. A key to proper soil sampling is to be consistent. It is important to try to always sample a given field at the same time of the year. A field may give different values in the spring vs. the fall.
2. Q: How frequently should I resample a field?
A: It depends…Every two or three years is OK for most fields. Sandy soils that have very low nutrient reserves or fields producing high value crops such as fruits and vegetables could be sampled every year. Also, sample every year when there is an aggressive soil build-up program, or when there is a significantly low fertilizer rate.
3. Q: Should I sample an area even if it can not be fertilized separately?
A: Maybe…It may be worth sampling a “poor growth” area in order to find out why it performs as it does. You may get a clue as to how to “fix” a poor area.
4. Q: Are there areas of a field that should not be sampled?
A: Yes. Avoid the following areas in the field, especially when they cannot be treated separately (see section on grid sampling).
• Old fertilizer bands, if possible (see section on sampling banded fields)
• Areas or fields that have had lime or fertilizer applied within about 30 days.
• Dead Furrows and end rows
• Stay 50 feet away from barns, roads, and fence rows, unless you intend to sample them separately for special purposes.
• Avoid areas where livestock congregate, or did in the past.
• Small, very poorly drained spots in the field
5. Q: Can I sample frozen soil?
A: Yes…While it is true that a frozen sample will probably show slightly higher levels (no more than 10%) of cations (K, Mg, Ca, etc.), the difference in recommendations will be small.

History of Soil Cation Balancing Theory

History of Soil Cation Balancing Theory

The concept of balancing soil cations began with research conducted from 1920 to 1970 by Dr. William Albrecht, a soil scientist at University of Missouri. In greenhouse experiments, he showed that liming does not merely correct soil pH, but also provides plants with the essential elements Ca and Mg, and can enhance plant uptake of N, P and trace elements.
Dr. Albrecht observed that cattle and wild bison thrive best in the tall grass prairie regions of the United States, whose soils are naturally rich in Ca (60-75% base saturation). In field experiments, liming increased forage yields only slightly, but substantially improved forage protein content and livestock weight gain. He also found that pasture soils should have about 10% Mg base saturation, and not more than 5% K. Too much K relative to Mg and Ca can cause “grass tetany,” a potentially fatal condition in cattle. Finally, Albrecht noted that mildly acid soils (pH 6.0-6.5) have more available nutrients than neutral soils (pH 7.0). These findings led to the Albrecht Formula shown on the previous page.
During the 1940s, Firman Bear and colleagues developed a similar base saturation ratio formula for optimal crop production on New Jersey soils. In their experiments, alfalfa performed well over a wide range of Ca:Mg and Ca:K ratios, as long as Mg and K base saturation did not fall below 10% and 5%, respectively. About 20% H (pH ~ 6.0) was needed to ensure adequate available manganese (Mn), especially on sandy soils. They assigned the remaining 65% of the CEC to Ca, partly because Ca amendments were inexpensive. This suggests that somewhat lower Ca and higher Mg or K might be acceptable on New Jersey soils.
Many farm consultants consider base saturation ratio to be an important factor in soil tilth. They base their reasoning on the fact that Ca ions promote aggregation (crumb structure) in clays, whereas K, Na, and (to a lesser degree) Mg promote clay dispersion, which leads to crusting. Therefore, on soils with high K or Mg, and Ca below 65% saturation, high-calcium lime or gypsum (calcium sulfate) is often recommended to add Ca and flush-out excess Mg and K. Some growers feel that these measures can improve soil tilth, relieve compaction, improve aeration and drainage, and restore beneficial soil life. Other benefits claimed for cation balancing include fewer weeds, pests and diseases; and better-quality produce and forage with higher soluble solids content (Brix), more nutritional value and longer shelf life.
Where is the evidence?

Critics of the cation balancing approach question its practical validity for several reasons.
First, most crops show little yield response to variations in base saturation ratio. In greenhouse and field experiments, millet, corn, wheat, barley, soybeans, alfalfa, lima beans, collard greens, lettuce and citrus nursery stock have tolerated soil Ca:Mg ratios as low as 1:1 or as high as 10:1 or more with no loss in growth or yield.
In the VABF field study, Ca amendments have not improved Brix values of broccoli, cabbage or tomato; have not enhanced crop uptake of P or micronutrients; and have had no visible effect on foliar diseases, insect pests or weeds. Effects of Ca on marketable vegetable yields have been inconsistent, and require further study.
Second, Ca deficiency is rarely seen in most crops. Blossom end rot in tomato and pepper, blackheart in celery, tipburn in lettuce and cabbage, cavity spot in carrot and parsnip, and bitter pit in apple are “calcium-stress disorders” that result from a localized Ca deficiency in the affected part, and are often not prevented by liming or gypsum.
Third, Ca amendments improve tilth mainly on saline soils, and on soils with high Na or extreme Mg levels. Such soils are rare in the southeastern US. The dispersive effect of Mg is slight, and often negligible in the field.
In the VABF study, the two farms with the highest Mg levels (27-30% Mg saturation) have the best tilth, with high porosity, many earthworms, and no hardpan within 24 inches of the surface. At the other three sites where hardpans are present, the effects of adding Ca have been inconsistent.
Finally, once sufficient levels of each nutrient have been achieved, and soil pH is good, adding lime or gypsum to adjust the soil’s base saturation ratio is economically unsound. Benefits sufficient to offset the cost of these amendments are unlikely.
Here is the evidence

Although soil tilth and crop yields can remain good over a wide range of base saturation ratios, the soil’s cation balance deserves attention for several reasons.
First, in high-rainfall regions like the eastern US, soils can lose 100 to 200 lb Ca per acre annually due to leaching. Mg and K can also leach. This may necessitate lime or other amendments to correct pH and replenish cations. Healthy, well-fed soil life, and deep-rooted crops in the rotation, can greatly reduces leaching losses, so that pH and cation levels remain stable for many years before liming is needed.
Second, the balance of Ca, Mg and K in most crops is influenced by the soil’s base saturation ratio. Too much of one nutrient can hinder plant uptake of the other two. Plants actively absorb K along the length of their root systems, whereas Mg and Ca enter only at the root tips. Thus plants may contain more K than Ca, even when the soil’s base saturation is 5% K and 65% Ca. When soil K saturation equals or exceeds that of Mg, crops may show Mg deficiency, and forages may pose the danger of grass tetany to livestock.
Third, ample Ca in plant tissues can reduce the incidence of tipburn and other Ca-stress disorders. Plants can relocate K and Mg from older leaves into growing points and developing fruit, but they cannot do the same with Ca. Thus the plant must maintain a steady flow of Ca from the soil to newly forming tissue. This flow can be interrupted by dry soil conditions, sudden wet/dry fluctuations, rapid vegetative growth, excessive soluble nitrogen (N) levels, or high soil K, Na or ammonium (NH4), which inhibit Ca uptake. Thus proper irrigation, and careful management of all of these nutrients may be required to control Ca-stress disorders.
Peanut is another crop with a high Ca requirement. After the developing pods “peg” into the soil, they must absorb Ca directly through the pod wall in order to develop normally. Peanut growers often apply 400 lb gypsum per acre at midseason to meet this need.
Fourth, ample tissue Ca enhances crop resistance to bacterial and fungal diseases, such as fusarium wilt and bacterial wilt in tomato, and botrytis mold in rose. Excessive tissue K levels may cancel the protective effect of Ca.
Fifth, plant root growth may become inhibited by Ca deficiency long before foliar symptoms develop. Roots may stop growing when they reach a highly acid subsoil with low Ca and toxic aluminum (Al) levels. Such acid subsoils are fairly common in parts of the southeastern US. Gypsum can relieve the subsoil Ca deficit, promote deeper root growth, and thereby enhance crop yield and drought resistance.
Sixth, although 20-30% Mg saturation may not hurt soil tilth, high K levels (>8%) may cause some clay-loam soils in our region to become more sticky. If K + Na + NH4 total 15% or more, tilth is likely to deteriorate. In the VABF study, the one soil in which gypsum has reduced soil strength (resistance to root growth) started with a K saturation of about 8%, which decreased to 6.7% in the high-Ca (gypsum) treatment.
Excessive soil K is a common problem on intensive vegetable farms. Organic farms that use large amounts of manure, hay mulch or compost from off-farm sources for many years, often accumulate too much P and K in their soils. Conventionally fertilized vegetable fields may also have excessive soil P and K. In either case, growing cover crops and recycling on-farm residues can provide organic matter and N without adding more P and K.
Finally, the effects of soil base saturation ratio on soil life are not yet fully known. Although proponents of the Albrecht formula claim that adding Ca to correct base saturation ratio will markedly stimulate beneficial soil life and humus formation, we have not yet seen this in the VABF study. However, longer-term studies may be required to evaluate possible effects of base saturation ratio on soil life.
Cation balancing is site-specific

For several reasons, it does not make sense to apply a single cation balancing formula to all farms. First, some types of soil clays hold onto calcium much more tightly than others. Montmorillonite, bentonite, vermiculite and smectite clays have high CEC, but they bind Ca quite firmly. Soils of the midwest and prairie regions are rich in these minerals, and may need 60-70% Ca saturation to provide sufficient crop-available Ca. Kaolinte clay has a lower CEC, but it holds Ca more loosely, so that soils rich in kaolinite may provide sufficient available Ca at just 40-50% Ca saturation. Mica clays such as illite are intermediate in their Ca-binding behavior. Most soils in the southeastern US have primarily kaolinite and mica clays, although there are exceptions.
Humus has very high CEC and it releases Ca to plants as readily as kaolinite. Thus building organic matter generally enhances Ca availability. In the VABF study, vegetable crops have obtained sufficient Ca from two soils with “low” Ca (<60% saturation) but good organic matter levels.
Second, care must be taken on sandy soils with low CEC to ensure adequate Mg and K availability. Gypsum can aggressively leach-out these two nutrients on such soils. In the VABF field study, adding Ca (gypsum) to a sandy Tidewater soil tended to reduce tomato yields and soil microbial activity, possibly by making Mg and K less available. Surprisingly, the gypsum has also gradually tightened an existing hardpan. For sandy soils, many consultants use a modified Albrecht formula, with base saturation of about 60% Ca, 20% Mg and 6-10% K.
Third, plant species differ widely in their needs for Ca. As mentioned earlier, peanuts, cabbage-family crops and some other vegetables require plenty of Ca, and may be sensitive to low soil Ca or Ca:K ratios. Cereal grains, corn, forage grasses, sweet potatoes and most soft fruits have a lower Ca requirement and do well in a wide range of soil base saturation ratios. Buckwheat, vetches, some clovers, phacelia, and some perennial broadleaf weeds have high tissue Ca concentrations, but their roots extract soil Ca quite efficiently, even where soil Ca availability or pH are low. Deep rooted cover crops (and weeds too!) with this capability help recover Ca that has leached into the subsoil.
Finally, the crop may “see” a different nutrient profile than that shown on a soil test. For example, healthy, well-fed soil life can “buffer” soil nutrient levels so that crops have good nutritional balance despite “low” or “excessive” levels of some nutrients on a soil test. Conversely, a compacted or biologically depleted soil may not release nutrients effectively. At one of our study sites, soil tests showed low P, K, and Ca, but good biological activity, and broccoli was well supplied with all of these nutrients. At another site, the compacted clay soil had over 70% Ca base saturation, yet tomato showed Ca deficiency.
Furthermore, different soil labs use different methods, so that one lab might rate the Ca level of a certain soil as “sufficient” and another rate it as “low.” Some soil consultants utilize the Morgan extraction method for estimating plant-available cation levels. Because soil-microbe-crop interactions are so complex, a plant tissue analysis often gives a better picture of the nutritional status of the crop than a soil test does.
Is Cation Nutrient Balancing Environmentally Sound?

Calcium amendments, like other inputs from off-farm sources, entail environmental costs, including fossil fuel use in transportation, as well as mining operations to extract limestone or gypsum. Ecologically conscientious growers seek to minimize their dependency on off-farm inputs, and to use primarily on-farm sources to maintain soil fertility.
Some soils are naturally lower in Ca and higher in Mg than recommended by Dr. Albrecht, because of the composition of underlying rocks and minerals from which the soils have developed. Adjusting such soils to conform to the Albrecht formula can require two to four tons of high calcium lime or gypsum per acre. For a larger farm, this could mean purchasing, mining and transporting (often from distances of 100 miles or more) many tons of mineral amendments – all at considerable cost to both farmer and environment. Good management of organic matter and soil life can keep many high-Mg soils productive and easily worked without the need for massive Ca inputs.
However, if a low-Ca soil is also prone to compaction, ponding, runoff or erosion, it makes ecological sense to correct the situation. Since calcium, organic matter and soil life work together to promote good tilth, several light applications (1000 lb lime or 500 lb gypsum per acre) in conjunction with green manure or other organic inputs, will give the best results. (1000 lb/acre = about 23 lb/1000 sq ft.) Adding a large amount of readily available Ca (gypsum or finely pulverized lime) at one time can temporarily inhibit soil life, and much of the applied Ca may leach away. A single heavy application of coarsely ground limestone is acceptable (since the Ca is released gradually over several years) and may be the most economical strategy for larger fields. Providing adequate organic inputs along with the Ca is essential, as a healthy, living soil retains Ca much better than does a worn-out soil.
For crops that are particularly dependent on plenty of available Ca, Albrecht sometimes recommended drilling or banding finely pulverized limestone near the crop row, at just 100 or 200 lb/acre (2-5 lb/1000 sq ft). This creates a Ca-saturated zone near the crop, which allows it to thrive despite the lower Ca levels in the bulk of the soil.
In conclusion

• Soil cation balance is important to soil, crop and livestock health. If the soil is managed to provide sufficient but not excessive levels of each nutrient, it is usually unnecessary to make the soil’s base saturation ratio conform precisely to the Albrecht formula.
• Cation balancing is site-specific, depending on soil type and crop mix. It cannot be prescribed for all farms by a single base saturation ratio formula.
• Moderately high Mg levels (up to 25 or 30% saturation) are usually not harmful to soil tilth or crop health. When acid soil pH warrants liming, it is wise to choose high-calcium lime if Mg is above 20% (25% for sandy soil), and dolomitic lime if Mg is below 10% (15% for sandy soil).
• High K (≥8% saturation) can make some clay-loam soils more sticky and prone to crusting or hardpan. Too much K relative to Ca may aggravate Ca-stress disorders in some vegetables, or reduce disease resistance. Soil K saturation equal or greater than that of Mg can lead to crop Mg deficiency, or grass tetany in livestock.
• Feeding and maintaining the soil as a living system helps maintain favorable cation levels, buffers pH, and reduces leaching losses of Ca, Mg and other nutrients.
• A crop foliar nutrient analysis can reveal the soil nutrient balance that the plant actually “sees.”
• The effects of base saturation ratio on the web of life in the soil needs further exploration.
• The experienced grower’s intuition and knowledge of his/her land may lead to better decisions than reliance on soil test results and base saturation formulas alone.

CEC Explained

CEC (Cation Exchange Capacity)

CEC is a calculated value that is an estimate of the soils ability to attract, retain, and exchange cation elements. In order for a plant to absorb nutrients, the nutrients must be dissolved. When nutrients are dissolved, they are in a form called “ions”. This simply means that they have electrical charges. Larger CEC values indicate that a soil has a greater capacity to hold cations (cation is a positive charged ion). Therefore, it requires higher rates of fertilizer or lime to change a high CEC soil.

When a high CEC soil has good test levels, it offers a large nutrient reserve. However, when it is poor, it can take a large amount of fertilizer or lime to correct that soil test. A high CEC soil requires a higher soil cation level, or soil test, to provide adequate crop nutrition. Low CEC soils hold fewer nutrients, and will likely be subject to leaching of mobile “anion” nutrients.
Base Saturation is a measurement, or estimate of the percent of the soil CEC that is occupied by a particular nutrient (nutrient saturation), or the sum of a group of nutrients (base saturation). This information gives us another tool to use in predicting the soils ability to provide adequate crop nutrients, and indicate needed changes in fertilizer or lime programs.