Effect of fire severity on hydro-erosive processes and black bean (Phaseolus vulgaris L.) productivity under slash-and-burn agriculture

Abstract

A traditional practice of slash-and-burn agriculture in tropical countries is discussed, focusing on its negative impacts, such as socioeconomic impacts, land conversion, deforestation, and soil erosion, etc. Despite the criticisms, slash-and-burn agriculture is still practiced in various regions worldwide. This study was conducted in the southeastern region of the State of Paraná–Brazil, to understand the relationship between soil burn severity, post-fire hydro-erosive processes, and crop yield. After burning, the following four treatments were set out: unburned, low, moderate, and high burn severity. Fire severity was determined using the burned area reflectance classification method (BARC). Before and after burning, biomass samples were collected and the soil was analyzed for chemical properties including pH, carbon content, base content, and cation exchange capacity). Ash cover was measured for each of the four fire severities. Under each treatment, six erosion plots measuring 10 × 1 m² were stablished (4 treatments × 6 plots = 24 plots). Hydro-erosive processes were monitored throughout the bean cultivation cycle (from November 2022 to February 2023). Soil moisture and crop yield were determined for each plot. Burn severity was heterogeneous although biomass was homogeneously distributed on the cultivation plots (CV 22 %). Soil loss was related to fire severity. Soil loss was 1.59 t ha ⁻¹ under low fire severity, 1.97 t ha ⁻¹ under moderate severity, and ∼ 4.67 t ha ⁻¹ under high severity, indicating that soil loss increased threefold from low to high fire severity. The lowest bean productivity was recorded under low fire severity (0.49 t ha⁻¹), followed by high fire severity (0.57 t ha⁻¹), whereas moderate burn severity had the highest productivity of 0.71 t ha⁻¹. The soil burn severity in the study area was patchy and significantly affected hydro-erosive processes, soil properties, and bean yield. The most important effect of fire was indirect.