"At Your Service" Newspaper Column

 

Michael R. Milam

Agronomy Specialist and County Program Director

For Daily Dunklin Democrat-At Your Service

November 20, 2007

Soil testing: frequently asked questions

            Soil testing is one of the most important tools available to the farmer. Soil testing helps prevent the over fertilization of the field which is costly and it is detrimental to the environment. It also helps prevent the under fertilization which would also have a negative outcome. Too little fertilizer results in less than optimum yields. Soil testing is a wonderful tool for reducing risk, and for making crop management decisions. Some of the information came from and MU  Guide G9112, “Interpreting Missouri Soil Test Reports written by John Lory, Peter Scharf, and Manjula Nathan. This guidesheet can be obtained on-line at http://extension.missouri.edu/explore/agguides/soils/g09112.htm. It can also be obtained by calling your local extension office.

There are some frequently asked questions related to soil sampling and interpreting soil test reports. Q: When is the best time to take a soil sample? A: Sampling can be done at anytime of the year. However, the fall is an ideal time because the soil is generally moist which make the samples easy to take. Fall sampling is also recommended because producers will have in their minds or their notes if special problems occurred. Soil testing in the fall is also recommended because if the soil is too acidic, agricultural lime can be applied to neutralize it prior to the next growing season.

Q: How often do I need to sample the soil? A: In general, soil should be tested every 3-4 years. However, guidelines are available for nutrient management under several of the Missouri and Federal Conservation programs. If problems are noted, it might be important to re-test in order to rule out nutrient related problems.

Q: Will hot, dry conditions affect the need for soil testing? A: Under droughty conditions it is possible that the plants did not use the available nitrogen and other nutrients since the plant could not take them up. So prior to planting, you can take a sample for nitrates and other nutrients to see if they are still in the soil. Also, with the previous crop being soybean, less nitrogen will need to be applied.

Q: How do I get a good soil sample? A: Problems with soil test results are often due to inadequate sampling. It is best to take 15 to 20 core samples per field. These cores can be mixed to form a composite sample. Fields with problem areas should be sampled separately as should different soil types within the same field.  If the fertilizer has been banded, then double the number of core samples to minimize taking a sample from the band.  Sampling should be to a depth of 6 inches.

Q: How do I sample soils in a no-till or conservation tillage situation? A: In situations where the fertilizer and lime are applied to the soil and not incorporated, there can be a difference in the results. The soil pH tends to be lower near the surface and then increase with depth. To account for this difference, it might be beneficial to sample at the 0-3 and the 3-6 inch depths. For example, samples taken at 0-6 inches might show an ideal soil pH. However, a 0-3 inch sample may show a higher concentration of acid in the top layer that would need a lime application to create a better environment in the root zone.

Q: Is there a difference between red lime and white lime? A: Yes. The red lime or dolomitic limestone contains both calcium and considerably more magnesium. The calcitic lime or white lime contains mostly calcium. Both are effective in reducing the excess soil acidity, but read your soil test report to see if recommendations call for calcium or magnesium. If your soil test recommendation does not specify either calcium or magnesium, then use the cheapest source.

Q: Why is ENM used on limestone suggestions? The ENM is the effective neutralizing material. Agricultural limestone is typically made up of varying particle sizes and varying degrees of purity. In general, the smaller the particle size, the more rapidly that the lime will react with the excess acidity and neutralize it faster. To determine the amount of lime needed, divide the ENM value by the guaranteed ENM from your lime dealer.  For example, if the soil test report calls for 800 lbs/acre of ENM and the guaranteed ENM value is 440 lbs/ton, then the amount needed is 1.8 tons per acre.

Q: I want to sign up for nutrient management under the EQIP program, are all soil test procedures or lab results equal. A: No. According to Glenn Davis, USDA NRCS Nutrient Management and Precision Farming Specialist, only fertilizer recommendation procedures and recommendations from the University of Missouri or other land-grant university are acceptable. This is statewide policy as of October 1, 2007. Commercial labs may use the Bray I Phosphorus procedure, analyze it with a colorimeter, and use the University of Missouri recommendations.

Q: If I do precision grid sampling can I get a break on the price of soil samples? A: Yes. Check with the University of Missouri Soil Lab located at the Delta Center for volume rates. They can be reached at (573) 379-5431.

Soil testing is very important for any successful farming operation. Soil Test, Don’t Guess is a good motto and can save producers money in the long run and protect the environment.

 

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