Nitrate and ammonium nutrition in chicory and rocket salad plants

To evaluate chicory (Cichorium intybus L.) and rocket salad [Eruca vesicaria (L.) Cav.subsp. sativa (Mill.)] capability to use ammonium-nitrogen (NH4-N) even in the absence of nitrate-nitrogen (NO3-N) in the nutrient solution, and the chances they offer to reduce leaf NO3, content, cultivated rocket and two cultivars of chicory ('Frastagliata', whose edible parts are leaves and stems, and 'Clio', a leaf hybrid) were hydroponically grown in a growth chamber. Three nutrient solutions with the same nitrogen (N) level (4 mM) but a different NH4-N:NO3-N (NH4:NO3) ratio (100:0, 50:50, and 0:100) were used. Rocket growth was inhibited by NH4 nutrition, while it reached the highest values with the NH4:NO3 ratio 50:50. Water and N-use efficiencies increased in rocket with the increase of NO3-N percentage in the nutrient solution. In the best conditions of N nutrition, however, rocket accumulated NO3 in leaves in a very high concentration (about 6,300 mg kg(-1) fresh mass). For all the morphological and yield features analyzed, chicory resulted to be quite unresponsive to N chemical forms, despite it took more NO3-N than NH4-N when N was administered in mixed form. By increasing NO3-N percentage in the nutrient solution, NO3 leaf content increased (5,466 mg kg(-1) fresh mass with the ratio NH4:NO3 0:100). On average, both chicory cultivars accumulated 213 mg NO3 kg(-1) fresh mass with the ratio NH4:NO3 100:0 and, differently from rocket, they showed that by using NH4 produce can be obtained very low in NO3 content.