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Influence of Added Aluminum on Carbon Dioxide Production in Tropical Soils¹

ABSTRACT

Aluminum added to a yellow-brown Latosol, as Al₂(SO₄)₃, at rates of 6.6, 16.5, and 33.0 meg /100 g of soil decreased soil pH from 5.9 to 4.6, 4.0 and 3.8, respectively. Carbon dioxide production during 35 days of incubation decreased with increases in H-ion concentration. In an attempt to separate the effects of H-ion displacement from that of Al-ion hydrolysis on microbial activity, Al-treated soils were left unadjusted, or adjusted to pH 4.0, 5.5 or 6.5 before incubation.

Carbon dioxide production decreased with increases in added Al when the soil pH was maintained below about 4.0. Aluminum precipitated rather rapidly in soils with a higher pH and the Al had little influence on CO₂ production. Less than 1 ppm of Al was extracted by 1N KCl when the final pH of the soil was above approximately 4.0 (as determined in neutral salt). Below this range, exchangeable Al increased with increases in amounts of Al initially added to the soil.

In a second experiment, a highly significant negative linear relationship was found between CO₂ production and increasing percentages of Al in mixtures of Al- and Ca-saturated Everglades muck. Furthermore, when Ca-saturated muck was adjusted to pH 4.0 with HCl, and incubated, the production of CO₂ was significantly greater than in Al-saturated muck adjusted to pH 4.0. Since exchangeable Al did not increase when the Ca-saturated muck was adjusted to a lower pH, but did increase when the pH of the Al-saturated muck was lowered, it appeared that Al had an influence on CO₂ production in these acid soils.

¹ Contribution from the Department of Soils, Florida Agr. Exp. Sta., Gainesville. Presented before Div. S-3, Soil Science Society of America, Nov. 17, 1964, at Kansas City, Mo.

² Former Graduate Assistant and Soils Technologist, respectively. The senior author is now Post-Doctoral Associate, Department of Soils, University of Missouri, Columbia.

Received for publication October 11, 1965. Accepted for publication January 4, 1966.