Since 1991 the total land dedicated to organic agriculture in Spain has grown exponentially to almost a million hectares. It is primarily dedicated to extensive crops (pasture, fodder, grains and legumes). Vegetable crops, tubers, vine and olive and nut trees also cover significant areas 1. Organic agricultural production seeks to provide top quality food while respecting the environment and maintaining soil fertility through optimal use of resources. Organic agriculture promotes the recycling of nutrients to minimize the quantity of nutrients imported to the farm. If any product is to be used to maintain soil fertility it should not be synthetic. Organic matter is a key for maintaining fertility in the soil-plant system 2. The demand for organic products in local and global markets is growing and is likely to gain significance in the future. However, organic fertilizer of sufficient quality to be used in this type of production is currently quite expensive, in spite of the increase in organic livestock farming.