Urochloa brizantha in silvopastoral and monoculture systems: soil, trees, and microclimate in an altitudinal gradient of the Amazon

Abstract

The aim was to determine the edaphic and microclimatic influence of an altitudinal gradient on the production of Urochloa brizantha in monoculture (MCS) and silvopastoral systems (SPS). Twenty-four farms were located along an altitudinal gradient from 150 to 1260 masl. The study reveals that, along the altitudinal gradient, neither altitude nor management system significantly affected the soil’s physical and chemical properties. However, significant differences (95% CI) in pH, phosphorus (P), potassium (K), and cation exchange capacity (CEC) were identified at mid-altitudes, associated with the presence of CaCO₃. These findings suggest edaphic stability in Amazonian pasture systems despite altitudinal and management variations, while highlighting the key role of CaCO₃ in soil fertility under these conditions. SPS exhibited high tree diversity, with more than 20 families and 40 species identified − 58% of which belonged to Simaroubaceae, Asteraceae, Fabaceae, and Malvaceae. The greatest tree diversity was concentrated at 170 m altitude, indicating greater ecological stability and resilience at lower elevations. Additionally, SPS showed a strong capacity to regulate the microclimate by lowering temperature and solar radiation while increasing relative humidity, in contrast to MCS. These microclimatic conditions promoted greater vegetative growth of U. brizantha, as reflected in highly significant differences (p < 0.0001) in leaf length compared to MCS. In contrast to expectations, the growth and development of U. brizantha did not significantly respond to soil properties, exhibiting similar performance in both acidic soils (pH ~ 4) and slightly alkaline soils (pH ~ 7.5), as well as across varying levels of P, K, and CEC. However, the altitudinal gradient had a notable influence, with the highest growth values recorded at mid-altitudes.