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Effects of Heating on Soil Chemical Properties and Growth and Nutrient Composition of Corn and Millet¹

ABSTRACT

Heating or burning has a wide variety of effects on soils, the magnitude of which is determined largely by the temperature to which the soil is heated and on soil properties. In parts of Africa, the practice is used on soils in the field to improve crop production. The objective of this study was to determine the effect of heating Alfisol and Mollisol soil materials on their chemical properties and on the early growth and nutrient composition of corn (Zea mays L.) and millet (Setaria italica) grown in the greenhouse. Heating the soils to 110°C decreased pH, but the pH increased when the soils were heated to 200 or 250°C. Organic matter and extractable Mg decreased while extractable NH⁺₄ and Mn and electrical conductivity (EC) increased greatly with heating. The effects on soil-test P and K and extractable Ca were small and variable, but the soils were already higb in these elements. Increases in extractable NH⁺₄ and Mn, EC, and pH probably came from both the destruction of soil organic matter and release from inorganic compounds in the soils. Heating soils to 110°C resulted in greater growth of both corn and millet, but heat treatments of 200 and 250°C suppressed growth. The increase in the growth of corn and millet was attributed primarily to moderate increases in extractable NH⁺₄ at 110°C. The suppression of growth with heat treatments of 200 and 250°C was thought to be due largely to excessive amounts of NH⁺₄. Extensive work on NH⁺₄ shows that certain levels of this form of N may be toxic to plants. Heating of soil was shown to be both heneficial and detrimental to the growth of plants. Crops may benefit from nutrients released when soils are heated, provided the amounts are not excessive. The detrimental effects observed in this study would not usually be noticeable under field practice, because only a small proportion of the soil volume is heated.

¹ Contribution from the Dep. of Agronomy, Univ. of Kentucky, Lexington, KY 40546-0091. Published as Jour. Paper no. 82-3-52 with approval of the Director of the Kentucky Agric. Exp. Stn.

² Graduate Research Assistant and Associate Professor of Agronomy, respectively.

Received for publication April 1, 1982. Accepted for publication August 13, 1982.