Autor(es):
Cubera, Elena 
; Nunes, Jorge ; Madeira, Manuel ; Gazarini, Luiz
Data: 2009
Identificador Persistente: http://hdl.handle.net/10174/3430
Origem: Repositório Científico da Universidade de Évora
Assunto(s): herbaceous biomass; shade; fertilization; irrigation
Descrição
In an open woodland in Portugal, the nature of interactions between Quercus ilex trees and herbaceous
plants was assessed during 2 years by studying how manipulation of incident solar
radiation, water and nutrient supply affect the herbaceous biomass and N, K, P, Ca, Mg, and Mn
concentrations. Measurements were carried out in three environments consisting of (1) open
grassland, (2) beneath the tree canopy, and (3) under artificial shade. Each of these environments
was subjected to two regimes of fertilization and two water levels in a factorial design.
The fertilizer treatment consisted of application of no fertilizer or a combination of 200 kg calcium
ammonium nitrate ha–1 (26% N) and 350 kg superphosphate ha–1 (8% P), while the water-supply
treatment consisted of either no irrigation or irrigation fortnightly from February 1 to April 30.
Grasses showed significantly lower nutrient concentrations than forbs. However, nutrient concentrations
of the whole herbaceous community were within the recommended ranges for cattle
nutrition. A negative effect of shade on herbaceous biomass production was observed. The
effect of watering on herbaceous biomass was less prominent than the effect of fertilization, irrespective
of the environment, suggesting that Q. ilex does not compete for soil-water resources
with herbaceous biomass in this ecosystem. Fertilization increased total biomass by 106%,
49%, and 97% in the open grassland, beneath the tree canopy, and under artificial shade, respectively.
During the first and second year, fertilization increased herbaceous P concentrations
by 24% and 83%, respectively, if compared with concentrations obtained at the unfertilized plots.
Higher K and Mg concentrations were observed in herbaceous plants beneath the tree canopy
than in the open areas, indicating a positive effect of trees on pasture quality. The positive and
negative effects of trees on understory forage are discussed.
