Soil acidification under some tropical agricultural systems. 1. Rates of acidification and contributing factors

Abstract

A paired site (developed v. undeveloped) approach was used to calculate acidification rates in several agricultural systems of tropical and subtropical Queensland. The systems considered were summer crop–winter fallow, grass or grass–legume pastures for hay production, tobacco, sugarcane, table grapes, and bananas. Mean acidification rates varied from -2·4 kmol H⁺ /ha · year for tobacco to 34·2 kmol H⁺ /ha · year for bananas. Acidification rates were higher than for comparable systems in temperate Australia.

Subsurface acidification occurred under all systems, and was particularly severe under bananas despite the surface application of at least 2·5 t lime or dolomite/ha· year. As bananas can be considered to be a generic perennial horticultural system, subsurface acidification may be a widespread problem in such systems despite surface applications of amendments.

There was a wide range in acidification rates within a particular agricultural system, suggesting that management practices can be manipulated to reduce acidification. As the N cycle terms were the major contributors to the acidification under cropping systems, N fertiliser management is likely to be the most critical acidification factor.