Response of Corn to Acidity Factors in Eight Tropical Soils

Abstract

The effect of soil acidity factors was determined on yields and foliar composition of corn grown on Ultisols and Oxisols typical of the Humid Tropics. Soil pH values increased from about 3.8 with a base saturation of around 20 percent to about pH 5 with a base saturation of around 70 percent based on cation exchange capacities determined with neutral ammonium acetate. The low pH values in relation to exchangeable base contents are explained by the presence of free salts. The level of aluminum saturation of the soil based on exchange capacities as determined with ammonium acetate decreased from 40-percent at about pH 3.9 to 0 at about pH 5.2. The Ultisols had a high content of exchangeable aluminum when acid but the more weathered Oxisols contained little aluminum. A very close relationship exists between exchangeable base (Ca + Mg) and aluminum values based on total exchange capacities determined either with ammonium acetate at pH 7.0 or by the sum of cations at a given pH permitting conversion of one value to another. Corn responded strongly to liming particularly on the Ultisols which had high exchangeable aluminum content when acid. Calcium content of the corn leaves increased with soil base content and with yields but foliar composition was not otherwise affected by liming. Corn yields increased with pH to about 5.2 at which pH level these soils contained essentially no exchangeable aluminum, with exchangeable base content as determined with ammonium acetate to about the 70-percent saturation level, and with decreasing exchangeable aluminum in the soil to essentially 0. Soil pH, exchangeable base, and exchangeable aluminum content were effective criteria for liming these soils.