Long fallows allow soil regeneration in slash-and-burn agriculture

Slash-and-burn is a typical soil management system in tropical regions, in which the use of fire and the fallow time are key factors for controlling the dynamics of the physical and chemical attributes of the soil. The present study evaluated the ability of the fallow period to regenerate the soil, making it similar to the soil of a mature native forest, and compared it with other agricultural soils using a slash-and-burn chronosequence. Soil samples (0-5, 5-10 and 10-20 cm) were collected in areas with slash-and-burn agriculture [2-year crop (cassava); 10 and 15-years fallow] and in nearby areas with eucalyptus forest plantation, agroforestry system and mature native forest.

Slash-and-burn agriculture does not alter soil bulk density; however, it reduces aggregate geometric mean diameter (GMD). A 15-year fallow can restore the GMD to values similar to those other areas. The sensitivity index of GMD shows the improvement of aggregation after a 15-year fallow. Total organic carbon decreases in a 2-year crop but increases in a 10-year fallow. A 15-year fallow increases particulate organic carbon and mineral-associated organic carbon compared to a 2-year crop. Total nitrogen, particulate nitrogen and mineral-associated nitrogen decrease in the years following the burning but increase throughout a 15-year fallow.

The results of the chemical and physical attributes evaluated indicate that a fallow period of 15 years or more after a crop cycle in slash-and-burn agriculture can restore the original soil conditions. The soil quality conservation in the slash-and-burn agriculture is superior to that of continued cultivation of agricultural crops, or monoculture plantations. © 2019 Society of Chemical Industry.