Humic Haplustox under different land uses in a high altitude environment in the Agreste region of Pernambuco, Brazil

Abstract

SUMMARYThe Garanhuns Plateau in the Agreste region of the State of Pernambuco, Brazil is characterized by humid climatic conditions due to orographic rains, unlike the surrounding semiarid region. These soils are subjected to intense agricultural use and are extremely important for the regional economy. This study was carried out in the municipality of Brejão in the Agreste region with the aim of assessing changes in humic Haplustox soils subjected to different land uses. Four plots with different vegetation covers (native forest, secondary shrubby vegetation (capoeira), traditional cropping system, and planted pasture) were selected, and samples were taken from a soil profile and four small pits surrounding it at each site. Physical and chemical properties were assessed, including aggregate stability, humic organic fractions, and a microbiological evaluation through determination of basal respiration, microbial biomass carbon, and metabolic quotient. The soils under study showed physical and chemical properties typical of a Haplustox, such as low nutrient content, low cation exchange capacity, and high levels of acidity and Al saturation. The total organic carbon (TOC) contents were high regardless of the type of land use. Aggregates < 2 mm were dominant in all the conditions under study. The TOC content was higher in the soil under capoeira, 43.91 g kg -1 on the surface, while 34.36 and 33.43 g kg -1 of TOC were observed in the first layer of forest and pasture soils, respectively. While the microbial biomass C (MBC) was greater than 700 mg kg -1 in the forest and pasture areas (in the 0-5 cm layer), and 588 mg kg -1 in the soil under capoeira, these numbers were not statistically different. In the cultivated soil area, there was a reduction of around 28 % in TOC and MBC contents. Agricultural activity contributed to degradation of the humic 1338 horizon, as can be seen from a significant decrease in the TOC and changes in the relative distribution of the humic fractions. In contrast, aggregate stability was not altered as a function of the different land uses; the soil under planted pasture and capoeira were similar to the soil under native forest. Humin was the most important humified fraction for C reserves, contributing over 40 % of the TOC in these soils.Index terms: land use, highland soils, humic substances, aggregate stability, microbial biomass C. RESUMO: LATOSSOLOS AMARELOS HÚMICOS SOB DIFERENTES TIPOS DE UTILIZAÇÃO EM UM AMBIENTE ALTIMONTANO NO AGRESTE DE PERNAMBUCOO Planalto de Garanhuns, no Agreste de Pernambuco, destaca-se por apresentar características climáticas privilegiadas, favorecidas pelas chuvas orográficas, distinguindose da região semiárida circundante. Essas áreas mais úmidas são conhecidas como "brejos de altitude" e intensamente utilizadas e importantes para a economia regional. Este trabalho foi desenvolvido no município de Brejão, Agreste de Pernambuco, com o objetivo de identificar alterações nos atributos de Latossolos Amarelos Húmicos, submetidos às diferentes formas de uso do s...

Soil Microbial Activity and Biomass in Semiarid Agroforestry Systems Integrating Forage Cactus and Tree Legumes

“…Due to the lower C:N ratio of this litter, it is rapidly decomposed and mineralized by microorganisms [37], which explains the greater microbial activity. The results found in this study are similar to those found in soils under native vegetation and pasture cultivation in the semiarid region of Pernambuco [38], indicating that agroforestry systems and cactus monoculture are sustainable and beneficial models for microbial biomass. In general, the dry season had a higher qM and lower C-mic:N-mic ratio, indicating a better efficiency of microorganisms in metabolizing organic matter [23].…”