INFLUENCE OF NITRATE AND AMMONIUM NITROGEN SOURCES ON GROWTH, NUTRIENT UPTAKE AND PHOTOSYNTHETIC ACTIVITY OF LUPIN (Lupinus albus L. var termis Forsk

A water culture experiment was carried out on lupin plants, to study the influence of different nitrate and ammonium ratios on growth, nutrient uptake and photosynthesis process, in respect of chlorophyll content and carbonic anhydrase activity (CAA). Nitrogen was applied in five NO₃ /NH₄ ratios : (100 : 00 ), (75 : 25) ,(50 : 50 ), (25 : 75) and (00:100). Results revealed that both shoots and roots dry weights wwere significantly increased as the portion of NO₃ in the growth medium increased. Also P and Mg concentrations in the shoots were increased with increasing NO₃. While, K and Ca in the shoots and K in the roots were increased with increasing NH₄ level. 75% of applied N in NH₄ form caused a decrease in Zn and Cu concentrations in the shoots. In contrast, Fe increased and no specific trend was observed for Zn , Fe and Cu in the roots. P uptake by shoots was not significantly affected, while P uptake by roots was significantly affected. Highest K uptake in shoots and roots was observed when NO₃ was the sole nitrogen source. Ca uptake by shoots and roots significantly increased when portion of NH₄ increased. Zn, Fe and Cu uptake by roots were increased significantly, when NH₄ portion increased. In addition, Zn and Cu uptake by shoots of lupin plants were increased significantly when plants were fed with nitrogen all in NO₃ from. Chl. a and Chl. ( a + b) showed the highest value when NO₃ was the sole source for nitrogen, except Chl b. which showed the maximum value when NO₃ was only 25% from applied nitrogen. In addition, CAA was significantly increased when 100% NO₃ was used in the growth root medium.