Soil Analysis:

Use A Soil-Testing Laboratory or A do-it-Yourself Kit?

pH Meters, Friend or Foe?

By W. Carroll Johnson III and Wiley C. Johnson

The importance of soil testing in establishing and maintaining a premium food plot is well documented. Soil acidity (low pH) and nutrient deficiencies are among the most common agronomic problems with food plots. This is not surprising given the frequent location of food plots in neglected areas such as forest openings, abandoned fields, and utility rights-of-way. Even after choosing quality seed of an adapted forage species, soil acidity and nutrient deficiencies will lessen the chances for a successful food plot. As managers of food plots become more educated, questions arise about soil sample analysis. Is soil analysis the exclusive domain of public and commercial soil-testing laboratories or can “do-it-yourself kits” be used as a substitute?

Soil-testing laboratories are linked to land-grant universities, and public funds help underwrite their operation. Public soil-testing laboratories usually require a nominal fee for basic nutrient analysis, which is sufficient for food plots. For example, the University of Georgia Soil-Testing Laboratory charges non-farmers $6.00/sample to analyze for pH, phosphorous, potassium, magnesium, calcium, manganese and zinc. Nitrogen is not routinely included in a soil analysis because available nitrogen is extremely transitory in soils; either rapidly taken up by plants or lost by leaching. Commercial soil-testing laboratories also provide similar levels of quality service and often return results much quicker than public institutions. The Whitetail Institute’s soil test laboratory, for example, performs soil tests for $9.95 and usually returns soil results in two weeks.

Public laboratories and reputable commercial soil-testing laboratories are equipped with state-of-the-art analytical equipment, staffed with trained professionals and exist for the sole purpose of analyzing samples for available nutrients. Soil analysis followed by a scientifically based fertilizer/lime recommendation is their mission and vocation. If these laboratories did not provide quality service, they could not exist or remain in business.

Soil-testing laboratories routinely process large volumes of samples in a short period of time. Unless you are able to personally deliver soil samples directly to the laboratory, samples will need to be mailed or shipped. Once the laboratory has completed analysis, results and recommendations are mailed, faxed or emailed back to the food plot manager. Allow ample time for samples analysis and subsequent fertilization when planning for food plot establishment or maintenance.

An analysis report from a soil-testing laboratory includes raw data, which is an actual numeric measurement of nutrient levels in the soil and a pH reading. The raw data will have little outright meaning to most people. The exception is pH, which within limits, is conceptually understood. However, the absolute amount of these nutrients in soil is not the complete story. The portion of the total amount of an element that is actually available to plants during the growing season is the critical value. Results of the various analytical procedures have been correlated with crop growth and yield in extensive field tests. Soil-testing laboratories use these correlations to make recommendations for fertilizer and lime. The recommendations include the need to fertilize/lime, which type fertilizer/lime to use and amounts. This “bottom line” advice provided by public and private soil-testing laboratories is arguably the most valuable, yet under-appreciated, service available.

The do-it-yourself kits are among the newest tools available to food plot managers. These kits vary in cost, complexity and analyses performed. A common type is an inexpensive handheld soil probe and pH meter. Another type of do-it-yourself analysis involves taking a composite soil sample, adding distilled water to make a soil slurry and measuring the acidity of the slurry with a different type of pH meter. The amounts of soil and distilled water are critical. Haste, inexperience and failure to exactly follow instructions result in inaccurate and inconsistent readings.

Among the more sophisticated do-it-yourself choices are portable soil analysis kits that measure the pH, nitrogen, phosphorous, potassium and calcium content in soils. These kits involve making water-soil slurry and then adding specific reagents to obtain a color reaction. The resulting colors are then compared to a standard chart. These do-it-yourself soil analysis kits are capable of distinguishing very low from very high nutrient content but are not very accurate in the mid-range of fertility. You probably can do as well by evaluating plant growth and past fertilization history.

The do-it-yourself kits have only one tangible advantage to the food plot manager – instant results. In theory, the do-it-yourself kits eliminate the time lag of using a soil-testing laboratory and provide instantaneous results.

If do-it-yourself soil analysis is your option of choice, you must continuously ask yourself:

 “Is the raw data accurate?”

“What does the raw data mean?”

The concept of do-it-yourself soil analysis for time-savings is appealing, but improper use and poor quality equipment can lead to grossly misleading numbers. The written instructions for using the do-it-yourself soil analysis kits must be followed to the letter. Even then, how do you know if the raw data are accurate? Public and commercial soil-testing laboratories have the analytical equipment and trained personnel to consistently provide accurate raw data. Furthermore, soil-testing laboratories have rigid protocols to calibrate analytical equipment with established chemical standards to ensure accuracy. Quality control is a hallmark of a reputable soil-testing laboratory.

Assume that the do-it-yourself analytical equipment is being properly used and provides accurate raw data. What does the data mean? Are fertilizers or lime needed? If needed, in what amounts? The do-it-yourselfer can search the published agricultural scientific literature and find those answers. However, that is a lot of trouble, especially when answers are readily available elsewhere from qualified sources.

To prove these points, we analyzed soil samples from a food plot in southern Georgia , comparing the service provide by the University of Georgia Soil-Testing Laboratory versus the output from an inexpensive soil pH meter. The handheld pH meter used in this comparison consisted simply of a probe inserted into moist soil, providing a pH reading. Soil cores were collected from several places in the food plot at depth of 6 inches and pooled into a composite sample (total soil volume of about 1/2 pint), and then submitted for analysis. The handheld pH meter was used at the same sampling points and the readings averaged.

There are several points to note in this real-world comparison. Specifically, the soil-testing laboratory provides a thorough picture of the nutrient status of the soil. The soil-testing laboratory report shows a low pH (very acidic soil) along with low levels of phosphorous, potassium, calcium, and magnesium. The sample cost is recurring $6.00/sample. The sample turn-around time is 9 days. In contrast, the handheld soil pH meter provided only one measurement; an instantaneous pH reading of 6.9 and the unit had a one-time cost of $24.99.

Note the major discrepancy in pH value between the two methods; pH 4.7 (soil-testing laboratory) versus pH 6.9 (handheld pH meter). Which is correct? The implications of soil pH are enormous (food plot success or failure can depend on it). Legumes will hardly survive at a pH of 4.7, while a reading of 6.9 is acceptable. Thousands of farmers whose livelihoods depend in part on accurate soil analysis rely on public or commercial soil-testing laboratories, and it is a safe assumption that the soil-testing laboratories know what they are doing. Remember, quality control is the universal trademark of a reputable soil-testing laboratory. Therefore, we strongly feel that the pH level of 4.7 measured by the soil-testing laboratory is accurate and the result (pH 6.9) provided by the handheld pH meter is grossly inaccurate. We used the handheld pH meter according to the written directions and it gave erroneous results – not to mention an incomplete picture of the soil nutrient status and no fertilizer/lime recommendations. Following the erroneous results and incomplete analysis from the hand-held pH meter would have likely resulted in a costly food plot failure. This is why the Whitetail Institute does not sell pH meters. They do not meet the rigorous standards necessary to be recommended.

We recognize the logistical difficulty in managing food plots when located a significant distance from home. Soil analysis on the spot using a do-it-yourself kit would certainly help, but there is potential for too much error during one of the absolutely critical phases of food plot establishment and maintenance. The accuracy, reliability and thoroughness of an analysis provided by a soil-testing laboratory far out-weigh the minor convenience of instantaneous soil test analysis using a do-it-yourself kit. Stick with the pros. It will always pay dividends. The Whitetail Institute Soil Testing Service is available by calling (800) 688-3030.