Growth and nitrogen recovery in the above-ground biomass of eleven self-reseeding annual legumes grown in a rainfed olive orchard

Most of the traditional dry-farmed olive orchards of the NE of Portugal are planted in shallow soils on sloping terrain. The olive yields obtained are usually low, due to the severe environmental constraints under which these orchards are grown. Growing olive trees in such hard conditions, may recommend the management of the orchards as organic, a low-input farming system from which the farmer profit can arise from the appreciation of the price of the olive oil. The natural soil fertility of these orchards is usually very low, being nitrogen the most limiting nutrient to the growth of the trees (Rodrigues et al., 2011). Objectively, to manage these orchards as organic and to maintain the soil fertility and the tree nutritional status in an acceptable level, there is a single option: the introduction of legume species as cover crops. Legumes can access atmospheric N2, due to the symbiotic relationship that they can establish with nitrogen-fixing bacteria (Russelle, 2008). In this work eleven self-reseeding annual legumes were introduced in a rainfed olive orchard in order to test their suitability to be used as cover crops. The legume species/varieties were grown as pure stand and managed without grazing, since currently the farmers of the region are not raising animals. The cover crops were shown in September 2009, and data on dry matter yield, nitrogen recovery, ground cover percentage, persistence of the sown species, …, are recorded for four consecutive growing seasons.

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