June 2000 . . .A new issue paper by the Council for Agricultural Science and Technology (CAST) helps pinpoint factors that need to be considered as farmers and others use soil tests as a guide to protecting the environment while producing economical food. The Relevance of Soil Testing to Agriculture and the Environment issue paper provides perspective on the increasingly important role of soil tests, which farmers have long used in making crop production decisions.

“This paper should make regulatory officials, policy makers, and environmental consultants, as well as farmers aware of some of the issues that are involved in using soil tests to make judgments about how to best produce food and fiber, and simultaneously protect the environment,” said Dr. Eugene Kamprath, who chaired the CAST task force of nine authors for the paper and is the William Neal Reynolds Professor Emeritus of Soil Science at North Carolina State University. “Soil tests for environmental interpretations are more complicated than for agronomic purposes. From an environmental standpoint, one has to consider the kind of fertilizer or animal waste material being applied, the type of soil, proximity to water bodies, hydrology, and erosion hazard.”

The paper calls for a comprehensive approach to evaluating issues and identifies areas where additional information is needed. One important issue involves the use of soil tests to determine application rates of waste, such as livestock and poultry manures, so the environment will not be harmed. Although research has demonstrated numerous benefits of using these products to enhance soil fertility, there is concern that the traditional practice of applying animal waste based on the nitrogen requirement alone may result in the buildup of certain nutrients, such as phosphorus, copper, and zinc.

Environmental interpretations should take into account the loss of nutrients from soils. For nutrient loss to occur from agricultural soils, both a source of the nutrient and a mechanism for transporting it to surface or ground water are needed. The CAST paper indicates that a key to effective management of nutrient pollution is to focus on the critical areas where these two requirements are met. The Phosphorus Index (P-Index) is an example of a tool being developed to use soil tests and other site-specific factors, such as erosion rates, to help identify critical source areas of nutrient loss and to manage them appropriately. According to the CAST authors, the ongoing national effort to develop a reliable P-Index addresses environmental concerns regarding nutrients in a way that is more economically and environmentally effective than proposals limiting nutrient applications based on soil-test levels alone. However, soil testing will remain the foundation of any successful attempt to understand and control nutrient losses from the soil.

CAST is an international consortium of 38 scientific and professional societies representing more than 180,000 member scientists. Its mission is to identify food and fiber, environmental, and other agricultural issues and to interpret related scientific research information for legislators, regulators, and the media for use in public policy decision making. More information on CAST and its numerous scientific reports are available at https://www.cast-science.org. Copies of the reports, including Relevance of Soil Testing to Agriculture and the Environment, are available from CAST at (515) 292-2125 or by e-mail at cast@cast-science.org.