Comparison between nitrate and ammonium nutrition in fennel, celery, and Swiss chard

To evaluate the chance to reduce leaf NO3 content and to increase capability to use NH4-N even in the absence of NO3-N in the nutrient solution, plants of two Apiaceae species, fennel (Foeniculum vulgare Miller var. azoricum Mill. Thell.) and celery (Apium graveolens L, var. dulce Mill. Pers.), and of one species of Chenopodiaceae, Swiss chard (Beta vulgaris L. var. vulgaris), were hydroponically grown in a growth chamber with three different NH4-N:NO3-N (NH4:NO3) ratios (100:0, 50:50, and 0:100), but with the same total N level (4 mM) for 14 days. Swiss chard growth was inhibited by NH4 nutrition and reached the highest values with the NH4:NO3 ratio 0:100. For all the morphological and yield features analyzed, fennel and celery resulted to be quite unresponsive to nitrogen (N) chemical form. Water use efficiency increased in Swiss chard and decreased in fennel and celery with the increase of NO3-N percentage in the nutrient solution. The dependency of N uptake rate on shoot increment per unit root was more conspicuous for Swiss chard than fennel and celery. All species took more NO3-N than NH4-N when N was administered in mixed form. In the best conditions of N nutrition, Swiss chard accumulated NO3 in leaves in high concentration (3,809 mg kg(-1) fresh mass). On average, fennel and celery accumulated 564 mg NO3 kg(-1) fresh mass with the ratio NH4:NO3 100:0 and showed that by using NH, produce having very low NO3 content can be obtained. By increasing NO3-N percentage in the nutrient solution, NO3 leaf content of fennel and celery increased remarkably (7,802 mg kg(-1) fresh mass with the ratio NH4:NO3 0:100).