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Agriculture in Transition: Grid Sampling

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Grid sampling is about as high-tech as we can get down on the farm. However, we must question whether it is high-tech agronomically. This agronomist says, “No, it is not.” In fact, I will try to convince you why it is not agronomically sound.


The system is set up through satellite global positioning and is often referred to as “site-specific farming.” It is designed to accurately pinpoint positions on the earth’s surface. The purveyors of this system are dividing farms into 31 /2-acre grid sampling patterns. While it may sound good to be able to test and balance your soils in small areas of 1 to 3 acres, let us review the concerns of using this system by asking some hard questions.

  1. Can spreading equipment change application rates fast enough to provide a uniform application within the 1- to 3-acre blocks?
  2.  Why are they providing only soil pH, phosphorous and potassium tests? Isn’t it important to also know a soil’s cation exchange capacity (CEC), base saturation of the cations, calcium and magnesium levels, P1 and P2 tests, sulfur and trace elements?
  3.  How can we adjust calcium and magnesium levels when all we have to work with are constantly changing soil pH levels?
  4.  How can anyone make a potassium recommendation if they do not know the CEC of all of the different soil types found on any given farm?
  5.  Are they implying that nutrient balancing beyond phosphorous and potassium is not important?
  6.  Why are they now recommending you sample your soils every fourth year instead of every third year?
  7.  How are they handling “nutrient stratification,” which can develop in no-till soils where almost no tillage is done?
  8.  How do they handle situations where the 3-acre area straddles very different soil types?
  9.  Zone-tillers plant in the center of old rows. After the second year, there are old and new rows 15 inches apart. Many of these farmers apply all of their fertility inputs while planting and use both liquid and dry fertilizer bands. After a few years of banding every 15 inches, where will they be able to pull a reliable soil sample? 
  10.  Who pays for the costly spreading equipment, the high cost of sampling and the unscrambling fees when the military changes the signals coming from the satellites?
  11.  Why are they making recommendations, regardless of your tillage system, that all of your fertilizers be broadcast rather than the more efficient method of banding while planting?

If high technology puts limits upon your yields it is not agronomically sound. Grid sampling does not serve a farmer well if it locks him into a simple soil analysis such as we used 50 years ago simply to save money or forces him to use an outdated broadcasting system.

A soil analysis that merely covers phosphorous, potassium and soil pH, along with recommendations for broadcast of all fertility inputs, is a practice we want to move away from. It makes more sense to spend our money on more efficient fertility management of the first three soil basics — soil aeration, soil water and soil life. These are the things that determine how well our plants can recover the fertilizers.

We need to look at all yield-limiting factors and remove them in their order of importance. Studies show that a lack of soil fertility is rarely the top yield-limiting factor. It does not seem sensible to spend money on something that may give no return.

About the Author:

Donald L. Schriefer passed from this life on July 30, 1998. He had spent more than five years battling acute leukemia, but he did not lie down and wait for death to come. He left this manuscript as a legacy to his lifelong friends — the
farmers — knowing that those left behind would have it published.

Making education an integral part of his personal philosophy, Schriefer contributed frequently to various agricultural publications and was well known for conducting numerous seminars and farm programs annually. He has previously written two books, From the Soil Up and Tillage in Transition.

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