Descrição
Olive tree (Olea europaea L.) is present in large areas of mainland PortugaL
predominantly in less-favored regions. In spite of the fact that irrigated areas are
currently increasing, most of the olive orchards are still cultivated under rainfed
conditions. The success of olive farming under rainfed conditions is mainly due to the
high capacity of olive tree to develop anatomical, physiological and biochemical
drought resistance mechanisms. Nevertheless, the productivity is low. We propose
cover cropping to control soil erosion, improve soil quality and fertility of rainfed oli\'e
orchards. Cover cropping is widespread in fruit farming in temperate climates and in
irrigated olive orchards, where water is not a limiting resource. The effects of cover
cropping were investigated on a 14-year-old olive orchard (Olea europaea L., c.
Cobrançosa) with 240 trees ha-1, grown under rainfed conditions. The commercia!
orchard was located in Mirandela, in the Northeast of Portugal (41 0 31' N; 7° 12' W).
Four different soil management systems were compared: (i) development of natural
vegetation, (ii) self-reseeding pasture species, such as subterranean clover and other
annual legume species with short growing cycle grown as cover crop; (iii) white lupine
cover crop; (iv) conventional tillage, included as the control treatment. We verified that
self-reseeding pasture cover crop improved the photosynthetic activity of the olive trees
in association with increases of stomatal conductance, the quantum effective efficiency
of PSI!, the photochemical quenching and the apparent electron transport rate. The total
leaf soluble protein content in the leaves was higher in trees with self-reseeding pasture
cover crop that may represent increased activity of antioxidant enzymes. The level of
lipid peroxidation, measured in terms of thiobarbituric acid-reactive substances
(TBARS) contents, was lower in pasture cover crop and in the control treatments during
the dry season. In early winter lupine cover crop and conventional tillage had higher
TBARS concentrations, revealing increased peroxidative damage. At this early stage of
the study, data support the use of cover crop in olive rainfed orchards, specially using self-reseeding pasture species.
; Correia, C.M. 
