Response of lucerne and sunflower on nitrate and ammonia nutrition in water and sand cultures at three intensities of solar radiation

agua ammonia ammoniac arena biomasa biomass biomasse contenido de materia seca dry matter content eau enzymic activity growing media growth inhibitors helianthus annuus inhibidores del crecimiento light light regimes light requirements luz medicago sativa necesidades de luz nitrate nitrate reductase nitrates nitrato reductasa nitratos nutrition des plantes ombrage plant nutrition regimenes de luz retardateur de croissance sable sand shading substrat de culture substratos de cultivo umbria urea uree water