Evolution of the soil chemical properties in slash-and-burn agriculture along several years of fallow

Abstract

Several studies have demonstrated the effects of slash-and-burn agriculture on soil chemical properties immediately or short-term after burning. This study aims to answer if: a) the slash-and-burn system affects soil chemical properties; b) management effects remain in a fallow chronosequence; and if c) these effects are restricted to the soil surface. The study was developed in the south-eastern region of the state of Paraná, located in southern Brazil. On-site, the land preparation was made through procedures comprising of fire, cropping, and fallow. The methodology was based on the chronosequence approach by different fallow periods: native forest, 30 days after burning, 2-year fallow, 5-year fallow, 7-year fallow, and 12-year fallow. The soil samples were collected at 0–5 and 5–10 cm depths for chemical analysis (pH, organic matter, ions availability (extractable phosphorus, potassium, calcium, magnesium and aluminum) and cation exchange capacity). The results indicate significant changes at 0–5 cm depth. The soil organic matter levels remained constant throughout the chronosequence. The direct effects of burning led to increased pH and nutrient availability (extractable phosphorus and calcium), which decreased within 2 to 5 years of fallow. The increase in basic cations was sufficient to guarantee the soil nutrient status up to 7 years of fallow. Successive slash-and-burn cycles in the same area caused an increase in soil sand content, and reduced cation exchange capacity.