AGRI-BRIEFS
  AGRONOMIC NEWS ITEMS
From Agronomists of the
Potash & Phosphate Institute
655 Engineering Drive, Suite 110
Norcross, Georgia 30092-2837
Phone (770) 447-0335

Spring 1998, No. 1

SOIL TESTS MUST BE CALIBRATED FOR 1998 YIELD LEVELS

Space-age farming is a hot topic! Trade magazines and newspapers are full of stories about computerizing our tractors and harvesters and linking them to orbiting satellites to tell us—what to do—when to do it—and how to do it as we move across the field. Technology is wonderful, especially when those computers are making decisions for us based on sound, up-to-date information.

But what if the basic information is not sound? It's like having a shiny new car with a 300 horsepower engine, but with no tires. From a distance the car looks great, but on closer inspection it becomes obvious that it isn't going far.

Soil testing gives basic information for crop production. It provides us specific data on nutrient levels and other soil conditions needed to formulate an agronomically sound fertilizer program. It is essential that soil tests be calibrated to today's high yield production systems. In fact, it would be counter-productive to use soil tests calibrated for 125 bushels per acre of corn when the yield goal is actually 200 bushels or one bale of cotton when the goal is three bales.

Soil test calibration is a formidable task because production technology is continually improving, management systems are changing, and improved varieties are being introduced each season. Therefore, overall production systems are constantly changing, resulting in higher and more efficient production. Soil testing must not just keep up, but should lead the way.

Calibration research requires multiple sites and site-years spanning a range of soil and environmental conditions. The work is labor intensive, not nearly as glamorous as computerized tractors, and calibration information is frequently difficult to publish in scientific journals because of its applied nature. As a result, years or even decades pass between calibrations of many cropping systems. Frequently, a new calibration study will result in substantial changes in fertilizer recommendations because the previous calibration was done at a much lower production level.

Potassium fertilization of cotton in California is a case in point. Newly published guidelines from the University of California following an intensive multi-county research and Extension program recommend up to 400 pounds of K2O per acre. Previously, state-wide guidelines for cotton were not available. Because of a lack of in-depth research information, some questioned whether any potassium at all should be applied. It is now recognized that up to half of the cotton acreage in the San Joaquin Valley is potassium deficient.

In Idaho, industry and university researchers are working together to provide a continuous source of up-to-date calibration data. They initiated the Cooperative Fertilizer Evaluation Program (CFEP, pronounced SEE-FEP) in which data are being collected from commercial fields. New phosphorus recommendations for potatoes have been recently published. The recommendations were substantially increased utilizing data generated through this program. Also changes are under consideration for potassium that would double the recommended K2O rates for comparable soil test values.

These are just two examples to illustrate the value of calibration research. In both cases, new research produced dramatically higher recommendations. Previous recommendations were obviously too low for optimum production. So as we continue to develop more space-age technology, let's not forget the basics_and what is more basic than a reliable soil test?


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For more information, contact Dr. Albert E. Ludwick, Western Director, PPI, P.O. Box 1326, Bodega Bay, CA 94923. Phone (707) 875-2163. E-mail: aludwick@ppi-far.com.
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