Soil Acidity and Liming: The Kamprath Approach.

During the 1960’s and 1970’s Dr. Kamprath and NC State were heavily involved in the USAID Trop Soils program, focused on expanding and increasing crop production in several developing countries in Central and South America. The soils in many of these areas are old, very acid, highly weathered soils, classified as Ultisols and Oxisols, many similar to those found in NC. Low pH and aluminum toxicity were major problems in many of the areas. In addition, locally produced ag lime was not often readily available for most farmers, and transportation costs were a significant expense to move lime and other inputs in to the developing interior areas such as the "Cerrado" of Brazil, to resolve pH and Al toxicity issues.

Liming recommendations in many areas in the developed World at that time, were being made to bring soils up to some "optimum" soil pH, often >6.5. A large portion of the underlying research supporting these recommendations was developed utilizing complex rotations relying on legumes such as clovers and alfalfa as the nitrogen source for subsequent corn or small grain crops. Work by NCSU soil scientists, including Dr. K, had indicated that Al in the soil solution was the primary factor reducing crop growth in many southeastern US and tropical soils, especially where nutrient availability did not rely primarily on native soil sources. In 1970, Dr. Kamprath published a landmark paper “Exchangeable aluminum as a Criterion for Liming leached Mineral Soils” which proposed applying 1.5 x the neutral salt exchangeable aluminum. This idea called for the application of significantly less lime than a set pH system, and was rapidly adopted in many regions of the world. Reactions to this idea, and subsiquent related work will be discussed.