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Soil Lab Selection

Soil lab selection: How does anyone choose the right laboratory? Aren’t they all the same? Should you send a sample to several different labs and average the results? How do you get the samples to a lab and what is the turnaround time? Some homework needs to be done here.

These are all questions that I hear on almost a daily basis. All labs are not the same. This does not mean that one laboratory is better than another. They all provide a different “menu” of services. It is important to find a lab that provides all of the services that you require. Are you just looking for a soil analysis, or do you also need an irrigation water test or tissue analysis?

Laboratories can also choose from a number of methods or “recipes” to obtain results. Which method would be best for your soil type or crop? “Presentation” of results can also vary greatly from one laboratory to another. It is important that you can read the report and make use of the information it provides. These are all questions that you should consider before choosing a laboratory.

Menu of Services

Packages with various soil parameters are usually available, plus some a la carte choices. This will vary greatly from one laboratory to another. I think we all agree now that there is a lot more to soil than pH. Therefore, look at what is included in the soil package you are requesting. Continue Reading →

Soil Testing: The Need for Total Testing

What many farmers probably don’t know about soil testing is that most soil tests only tell us what is soluble in the soil. They do not tell us what is actually there in the soil, no matter what fertilizer salesmen might like to imply. To find out what is actually there requires a total acid digest similar to what is used for plant tissue analysis. Mining labs run these total acid di­gests on ore samples which are crushed, ground and extracted with concentrated nitric and hydrochloric acid solutions, but a mining assay does not determine total carbon, nitrogen and sulfur as a plant tissue analysis would. These ele­ments need a separate procedure essen­tial for evaluating soil humic reserves.

Total soil testing is key to understanding your soils’ needs.

Most soil tests measure total carbon, which then is multiplied by 1.72 to calcu­late soil organic matter. This assumes that most of the carbon in the soil is humus of one form or another. While this may or may not be true, determining the car­bon to nitrogen, nitrogen to sulfur, and nitrogen to phosphorus ratios is a good guide for evaluating organic matter, and this requires testing total nitrogen, sulfur and phosphorus as well as carbon.

While carbon in almost any form is a benefit to the soil, it helps enormously if it is accompanied by the right ratios of ni­trogen, sulfur and phosphorus. Though these ratios are not set in stone, a target for carbon to nitrogen is 10:1, for nitro­gen to sulfur is 5.5:1 and for nitrogen to phosphorus is 4:1. This works out to an ideal carbon to sulfur ratio of 55:1, and a carbon to phosphorus ratio of 40:1. Because soil biology is very adjustable these targets are not exact, but achieving them in soil total tests is a good indica­tion of humus reserves that will supply the required amounts of amino acids, sulfates and phosphates whenever the soil food web draws on them. Continue Reading →

More Accurate Soil Testing

soil testingSoil testing that determines needed fertilizer will measure nitrate in the soil, but tests don’t sufficiently account for soil microbes, which mineralize organic nitrogen and make more of it available to a crop. As a result, farmers often apply more fertilizer than necessary.

Richard Haney, a U.S. Department of Agriculture soil scientist in Temple, Texas, has developed soil test that replicates some of the natural processes that occur in a field and accounts for microbial activity, along with measuring nitrate, ammonium (NH4) and organic nitrogen.

The new soil test is known as the Soil Health Tool. It involves drying and rewetting soil to mimic the effects of precipitation. It also uses the same organic acids that plant roots use to acquire nutrients from the soil. The testing tool measures organic carbon and other nutrients, accounts for the effects of using cover crops and no-till practices and works for any crop produced with nitrogen or other types of nutrient fertilizer. For more information visit http://www.ars.usda.gov/is/pr/2014/140710.htm

This article appears in the September 2014 issue of Acres U.S.A.