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Manjula Nathan
University of Missouri
Plant Science & Technology
(573) 882-3250

Have You Tested Your Soil? Soil Fertility Summary Trends in Missouri for 2009 Prompts That You Should!

Manjula Nathan
University of Missouri
(573) 882-3250

Published: March 16, 2010

Spring is the time when normally the labs get flooded with soil samples for testing. Even though fall sampling is ideal for farmers, as it gives the starting point to plan for next year's nutrient management plan, we have many who wait until spring to test their soils. Last year, the excess rainfall during the months of September and October delayed harvest and the cooler temperatures that followed made it nearly impossible for producers to sample their fields in fall. To add to the problem, the winter weather conditions that persisted until mid February prolonged frozen soil conditions, causing further delays in sampling in early spring.

The soil fertility summary provides a valuable index of the soil fertility status of Missouri farmland and identifies broad soil fertility trends in the state. The trends in soil fertility status summary in the state for 2009 emphasize the importance of soil testing (Table 1). Of the 18,615 field crops samples tested by the MU Soil Testing Labs in the state during 2009, about 30% tested very low to low in soil pHs (less than 5.3) indicating lime should be applied for economically viable crop production. Another 37% of the samples received tested medium in soil pHs (5.4 to 6.0), and is likely to need lime to avoid profit loss.For example, the desired soil pHs range for alfalfa and row crops is between 6.1- 6.5. The lower soil pH will hinder alfalfa establishment and nodulation. The statewide trend in soil P indicated 49% of the samples tested low to very low, and P fertilizer is essential to avoid profit loss by crops. Another 23% of the P tests were medium (23 to 45 lbs of P/ac), and indicate P fertilizer is required for economic crop production. The desired soil P levels for row crops, small grains, and alfalfa are 45 lbs/ac and for forages are 40 lbs/ac. The majority of soils (47%) in the state tested medium in soil K (111to 220 lbs/ac) and 17% tested low to very low (less than 110 lbs/ac) and indicate K fertilizer will be required to avoid profit loss by crops. In Missouri the soil organic matter (OM) tests are used to estimate N availability in soil. The N credit from soil OM varies depending on soil texture. A general rule of thumb is every 1% of soil OM in the soil will release about 20 lbs of N/ac for crop. The majority of the soils tested had medium levels of soil OM (2 to 2.9%).

Table 1. Statewide Soil Fertility Status Summary in Missouri Based on Samples Received by the MU Soil Testing Labs in 2009
Test Very Low Low Medium High Very High
-----------------------Percentage of samples-----------------------
pHs 2 25 37 35 0
Bray P, lbs/ac 34 15 23 13 15
Soil K, lbs/ac 3 11 39 26 21
Soil OM, % 1 16 47 23 13
pHs: Very low less than 4.5; low 4.5 to 5.3; medium 5.4 – 6.0; high 6.1 – 7.5; very high greater than 7.5
P1: Very low less than 14 lb/ac; low 14 – 22 lb/ac; medium 23 – 45 lb/ac; high 46-70 lb/ac; very high greater than 70 lb/ac
K: Very low less than 65 lb/ac; low 65 – 110 lb/ac; medium 111 – 220 lb/ ac; high 221- 330 lb/ac; very high greater than 330 lb/ac
OM: very low less than 1; low 1-1.9:%; medium 2.0 % to 2.9%; high 3.0 – 4.0 %; very high greater than 4%

If you are going to apply nutrients in spring you need to know how much to put on. Without soil testing, nutrient applications are a guess, and there is no room for guessing in today's atmosphere of narrow margins due to varying fertilizer prices, and public concern of the environmental pollution. Testing soils reduce the risks involved with misapplying nutrients. What kind of fertilizer do you need to achieve your yield goals? Well, a good place to start would be the MU Soil and Plant Testing Lab.

Soil testing is a farmer's best guide for the wise and efficient use of fertilizer and soil amendments. A soil test is like taking an inventory of the nutrients available to plants, which are too high, too low, or just right. While plant growth and prior yields may offer clues to nutrient availability, a farmer won't precisely know until they test their soil. Although soil-testing kits are available in garden centers, laboratory testing is more reliable, and the results from laboratories are accompanied with specific interpretations and recommendations.

Soil fertility fluctuates throughout the growing season each year. The quantity and availability of mineral nutrients are altered by the addition of fertilizers, manure, and lime in addition to leaching and de-nitrification losses. Furthermore, large quantities of mineral nutrients are removed from soils as a result of plant growth and development, and through the harvest of crops. The soil test will determine the current fertility status and also provide the necessary information needed to maintain the optimum fertility year after year.

Soil testing takes the guesswork out of fertilization and is extremely cost-effective. It not only prevents over-spending on unnecessary fertilizers, but it also eliminates the over-usage of fertilizers, hence helping to protect the environment.

Soil samples can be taken in the spring or fall for established sites. Although it's best advised to test in fall and early spring, it can be done anytime soil is not frozen, barring recent fertilizer or lime applications. For new sites, soil samples can be taken whenever the soil is workable. Optimally, Fall is the best time to test, allowing ample time to apply lime to raise the soil pH.

As clearly evident from the statewide soil fertility status summary, soil testing is strongly recommended for field crops. The cost of soil testing is minor in comparison to the cost of seeds and labor. Routine fertilizer or lime applications can result in excessive soil nutrient levels or deleterious soil pH. For example, many fertilizers tend to have lower soil pH, and after several years of fertilization the pH may drop below desirable.

The test results are only as good as the sample taken. It is extremely important to provide a representative sample to the testing lab so that a reliable test and recommendations can be made for the entire area. This can be accomplished by submitting a composite sample. Take 15 random samples in a zigzag pattern at plow depth; mix well and submit a sub-sample from to the lab. We recommend that you divide your field and submit one sample for each 40 acres.

Testing your soil for nutrients and pH is important to provide balanced application of nutrients, while avoiding over application. At University of Missouri Soil Testing Laboratory we offer a regular fertility test that includes measurements of pH, lime requirement, organic matter, available phosphorus, potassium, calcium, magnesium, and cation exchange capacity. Soil pH greatly influences plant nutrient availability. Adjusting pH often corrects the nutrient problem for most plants. The optimum pH for most plants is between 6.0 and 7.0. The lime requirement measurement indicates the amount of amendment (usually lime) necessary to correct a pH problem. Organic matter has several roles in the soil; generally the more organic matter the better. Nitrogen recommendations are based on the organic matter level. Phosphorus, potassium, calcium, and magnesium are all essential plant nutrients. The cation exchange capacity (CEC) value is a measure of the soil's ability to hold nutrients.

Test costs vary according to the number of nutrients tested. The University of Missouri Soil Testing Laboratory charges $10.00 (when submitting directly to the lab) for a regular fertility test. Several other specific analyses are available. These include but are not limited to soil analysis for sulfur, micro-nutrients (Zinc, Iron, Copper, Manganese, Boron), salt content (electrical conductivity), heavy metal analysis, and soil texture. Test reports provide interpretation and nutrient recommendations. The turnaround time for a soil test is 24 hours. Customers have to add mailing time to get the reports by mail.

You can contact your Regional Agronomy/Horticulture/Natural Resources Specialist or local County Extension Office to obtain Sample Information Forms and boxing materials, and can submit samples through their offices. The Regional Specialists at your local Extension Offices can be a source of information for interpreting and personalizing your soil test reports and recommendations. Samples can be also submitted directly to the University of Missouri Soil Testing labs at 23 Mumford Hall, Columbia, MO 65211 (Tel: 573-882-0623). Samples can also be submitted to the Delta Soil Testing Lab located the Delta Research Center at Portageville or mailed to them. Every sample submitted should have a sample information form duly filled. Samples submitted directly to the lab should be accompanied by a check written in favor of MU Soil Testing for the amount due.

The lab maintains a comprehensive web site at http://soilplantlab.missouri.edu/soil/. It includes information on how to collect soil and plant samples, and how and where to submit them. The web site provides a list of services, pricing, and sample information forms, as well as contact and location information. The lab also provides web access to soil test results with a specifically assigned password for clients upon request. Results can also be sent by e-mail.

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REVISED: April 6, 2012