Spatial variability and changes in carbon stocks of a Regosols (Psamments) cultivated with sisal

ABSTRACT Information on spatial variability and soil carbon stocks after the conversion of Caatinga vegetation to different cropping systems is scarce. This study aimed to characterize the spatial variability and to evaluate the changes in carbon stocks and the emission of greenhouse gases after the conversion of Caatinga vegetation with different sisal cultivation systems. The study was carried out in three areas in the city of Valente, Bahia, two areas that had been cultivated for 20 years with sisal in either a traditional (TSC) or alternative (ASC) system, and the third area containing natural Caatinga vegetation. The cultivated soils were sampled at 40 soil sampling points with 15 × 10 m spacing at depths of 0-0.20 and 0.20-0.40 m. Total organic carbon (TOC) stocks had spatial dependence and the isoline maps allowed the variability in the studied depths to be analyzed. The conversion of Caatinga vegetation to sisal cultivation using traditional farming systems caused a 30% decrease in soil TOC stocks. Moreover, the alternative culture system caused an 11% increase in soil TOC stocks. The emission factor or carbon absorption due to changes in land use after 20 years was 0.66 t ha-1 yr-1 of carbon in the traditional farming system and -0.25 t ha-1 yr-1 of carbon in the alternative culture system.摘要：针对卡廷加（Caatinga）植被转换为不同种植系统后土壤空间变异与碳库的相关研究资料仍较为匮乏。本研究旨在阐明卡廷加植被转换为不同剑麻种植模式后的空间变异特征，并评估其土壤碳库变化及温室气体排放情况。本研究于巴西巴伊亚州瓦伦蒂市的三块样地展开：其中两块样地分别采用传统（TSC）与替代（ASC）剑麻种植系统，耕作时长均达20年；第三块样地保留原生卡廷加植被。耕作样地的土壤按0-0.20 m与0.20-0.40 m两层采集，采样点间距为15×10 m，共布设40个土壤采样点。总有机碳（TOC）储量具有空间依赖性，通过等值线图可对不同土层的空间变异特征进行分析。相较于原生卡廷加植被样地，采用传统种植模式的剑麻田土壤总有机碳储量下降30%；而采用替代种植模式的样地土壤总有机碳储量则提升11%。经20年土地利用变化后，传统耕作系统的碳排放因子为0.66 t C ha⁻¹ yr⁻¹，替代种植系统的碳吸收因子为-0.25 t C ha⁻¹ yr⁻¹。