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The (Dirt) Doctor Is In

By Paul Rodman (paulgrowJune 13, 2011
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I have always been a big advocate of soil testing, I was thrilled when I was recently invited to tour the Michigan State University Soil and Plant Nutrient Laboratory on the MSU campus in East Lansing, Michigan. It was a very interesting experience.

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Would you go to the drugstore to buy a handful of different medications and take them without checking with your doctor?  Most of us would not do that, yet many homeowners and gardeners will go to the local big box store or garden center and purchase soil amendments such as fertilizers, fungicides and such without having a clue chemical makeup of their soil. I have heard a number of gardeners state that they lime their garden soil each year to "sweeten it" by adding lime you raise the pH of the soil which can effect greatly the crops that you grow in that garden.

I have the opportunity to speak to various garden clubs throughout the area; I was surprised at the number of gardeners who have never had a soil test conducted on their lawns and gardens.

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The test results are analyzed by computer

The soil test is an excellent measure of soil fertility. It is an inexpensive way of maintaining good plant health and maximum crop productivity. Soil fertility fluctuates throughout the growing season each year--the quantity and availability of mineral nutrients are altered by the addition of fertilizers, manure, compost, mulch and lime or sulfur, in addition to leaching.

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Lab manager Jon Dahl shows how samples are prepared for testing 

Most turf grasses, flowers, ornamental shrubs, vegetables and fruits grow best in slightly acid soils with a pH of 6.1 to 6.9.

Most soil nutrients are readily available when soil pH is at 6.5. When pH rises above this value, nutrient elements such as phosphorus, iron, manganese, copper and zinc will become less available. When soil pH drops below 6.5, manganese can reach a toxic level for some sensitive plants.

The soil test takes the guesswork out of fertilization and is extremely cost-effective: here it costs $12 for the lawn and garden test which includes pH, lime requirement, P, K, Ca, Mg & recommendations. It alos provides the CEC which is the indicator of the nutrient holding capability of the soil.

It not only eliminates the waste of money spent on unnecessary fertilizers, but also eliminates over-usage of fertilizers, hence helping to protect the environment.

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Samples are kept on file for a short period of time In the event a retest is needed

FAQ about soil testing
  • Soil testing is an important diagnostic tool to evaluate nutrient imbalances and understand plant growth.
  • The most important reason to soil test is to have a basis for intelligent application of fertilizer and lime.
  • Testing also allows for growers and homeowners to maintain a soil pH in the optimum range (6.0-7.0), which keeps nutrients more available to the plant for growth.
  • Protection of our environment - We cannot afford to pollute our surface and ground waters by indiscriminate application of phosphorous or nitrogen fertilizers, for example.
  • Cost savings - Why apply what you don't need? Soil test results provide information about the soil's ability to supply nutrients to plants for adequate growth, and are the basis of deciding how much lime and fertilizer are needed.

What is being tested in a soil sample?

  • The regular soil test includes determination of soil pH, available phosphorus, potassium, calcium, and magnesium levels as well as recommendations for lime and fertilizer. Other soil tests are available at supplemental costs, such as, organic matter, zinc-manganese, etc.

How do I know if the test results are accurate?

  • The lab takes various quality control measures to ensure the accuracy of results. Soil with predetermined nutrient levels is tested every 20 samples to provide an accuracy check.
  • MSU recommends testing soil every 3 years. If recent results are not consistent with past results, notify your county MSU Extension agent or the lab within one month to rerun the questioned test.

Why doesn't the regular MSU soil test include nitrogen analysis?

  • Soil nitrate levels are the best indicator of nitrogen availability. Because these levels fluctuate widely depending on rainfall and soil temperature, the best time to take soil nitrate samples in while the crop is growing. within two weeks of supplemental nitrogen applications.
  • A soil sample taken months ahead of this time will not provide an accurate measure of the nitrogen available to the plants.

How does the lab make nitrogen recommendations?

  • Nitrogen recommendations are based on the past and present crops grown plus the yield goal for the crop to be grown.
  • Less nitrogen is recommended when the previous crop was a legume, because they add nitrogen to the soil. 

Where can I get my soil samples tested?

Contact your county extension office for instructions and a test kit.

 


  About Paul Rodman  
Paul RodmanPaul Rodman has been gardening for over 45 years. He is an Advanced Master Gardener, and American Rose Society Consulting Rosarian. He is President Emertius of the Western Wayne County Master Gardener Association in Wayne County, Michigan. He currently serves as the greenhouse chairman of this group. Rodman has amassed over 5500 volunteer hours in the Master Gardener program. Rodman is the garden columnist for The News Herald newspaper, in Southgate, Michigan. He has also written for the Organic Gardening.com web site. He is a certified Master Canner and has taught classes on Home Food Preserving for 7 years. He has lectured on various gardening topics throughout southeastern Michigan. His favorite pastime is teaching children about gardening. For the past several years he has conducted classes for second grade students teaching them about subjects ranging from vermi-composting to propagation.

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