This project deals with the introduction of cover crops in rainfed olive groves. The species used should be able to reduce the competition for water and contribute to the improvement of soil fertility. Legumes are annual species that can meet both characteristics: they are comparatively less competitive than grasses for water and fix atmospheric N, contributing to solving the main problem organic orchards management, i.e., the N fertilization. In addition, the cover crops may sequester atmospheric carbon, which can be accounted for Portugal achieving its commitments under the Kyoto Protocol.
Two different types of plants are tested in this project: self-reseeding annual legumes, such as subterranean clover, and other species, such as lupine, often used in Portugal as a green manure. A problem related to the management of the self-reseeding annual legumes, is the fact that growers do not have livestock. This kind of legume species are often used in pastures, being these farming systems extensively studied. However, experience in the management of self-reseeding annual legumes in dryland olive groves, through cutting or herbicide use, as proposed in this project, is practically nil. For lupines, although there is some tradition in its use in olive groves, we must learn to manage it as cover crop maintaining acceptable levels of competition for water. In practice, it is necessary to define the best time to cut it in order to balance N fixation and water loss by plant transpiration.