BIOGENIC AND PHYSICOGENIC AGGREGATES UNDER DIFFERENT CROPS WITH BLACK OAT IN NOVA FRIBURGO, BRAZIL

ABSTRACT The objective of this study was to evaluate the efficiency of black oat (Avena strigosa Schreb) crops in recovering soil aggregation, and quantify the nutrient contents in aggregates considering their formation pathways (biogenic and physicogenic) in crop areas in a mountains environment in the municipality of Nova Friburgo, RJ, Brazil. The landscape was stratified into two sections for the study: upper, two areas with black oat crops, one fertilized and one not fertilized one not fertilized, and one adjacent forest area representing the original soil conditions; and lower: one fertilized area with black oat, and one fertilized area with black oat intercrops with oilseed radish (Raphanus sativus L.) and vetch (Vicia sativa L.), and one adjacent forest area representing the original soil conditions. The aggregates were separated according to their formation pathways, quantifying the weight percentage of each formation pathway. The aggregate stability and nutrient and organic carbon contents were evaluated. The fertilized area in the upper section had the highest biogenic aggregate percentage, which was associated with the highest total organic carbon contents, and soil fertility. This area also had the highest weighted mean diameter (WMD) and geometric mean diameter (GMD) of aggregates. The intercrop area in the lower section had the highest biogenic aggregate percentage and the lowest P, Ca+2, Mg+2, and K+ contents in the aggregates. The management systems affected the aggregate formation pathways. Morphological classification is an important tool for the monitoring of soil management. The black oat crops increased the biogenic aggregate formation, which become reservoir of nutrients.摘要 本研究旨在评估黑燕麦（Avena strigosa Schreb）作物对土壤团聚体结构的恢复效能，并针对巴西里约热内卢州新弗里堡市（Nova Friburgo）山地环境中的作物种植区，依据团聚体的形成路径——生物成因团聚体（biogenic aggregate）与物理成因团聚体（physicogenic aggregate）——量化团聚体中的养分含量。本研究将研究区域的景观划分为两个区段：上坡区域包含2个黑燕麦种植区，分别为施肥区与未施肥区，以及1块毗邻的森林区域，代表原始土壤条件；下坡区域包含1个单作施肥黑燕麦种植区、1个与油料萝卜（Raphanus sativus L.）和野豌豆（Vicia sativa L.）间作的施肥黑燕麦种植区，以及1块毗邻的代表原始土壤条件的森林区域。研究人员依据形成路径对团聚体进行分离，并量化各形成路径的重量占比，同时测定了团聚体稳定性、养分及有机碳含量。上坡区段的施肥区拥有最高的生物成因团聚体占比，该指标与最高的总有机碳含量及土壤肥力水平显著相关，且该区域团聚体的加权平均直径（weighted mean diameter, WMD）与几何平均直径（geometric mean diameter, GMD）同样为所有区域中最高。下坡区段的间作区拥有最高的生物成因团聚体占比，但其团聚体中的磷（P）、钙离子（Ca²+）、镁离子（Mg²+）与钾离子（K+）含量最低。土壤管理系统会对团聚体的形成路径产生显著影响。形态分类法是监测土壤管理措施的重要工具。黑燕麦作物可促进生物成因团聚体的形成，此类团聚体可作为养分储存库。