Influence of nitrate and sodium chloride on concentration and internal distribution of mineral elements in broad bean (Vicia faba L.) and chickpea (Cicer arietinum L.)

The objective of the research was to evaluate the effect of nitrate and salt as limiting factors for the recycling of nutrient solutions in a hydroponic system. A broad bean (V. faba) and two chickpea (C. arietinum) cultivars (desi early) and kabuli (late flowering) type), were subjected in a factorial designed experiment to three levels of nitrate, and NaCl in the nutrient solution. The treatments were administered in a recycled nutrient solution. In the hydroponics system employed recycled nutrient solution was supplied freshly every 45 minutes. Nutrient solutions were fully refreshed every 2 weeks or when the initial volume declined by about 10 % due to transpiration. Increasing nitrate levels increased the vegetative yield of both chickpea cultivars in each salt level. Salt always decreased chickpea yields. At only 12 mM NaCl in the nutrient solution seed yield of the kabuli type was reduced by a factor of 8 while in the desi type yield was reduced only by a factor of about 2 to 3. Increasing nitrate in the solution counteracted the salt effect on both vegetative and seed production by up to a factor of 3. In contrast to chickpea the vegetative and seed yield of broad bean was less sensitive to salinity. The distribution of mineral nutrients between leaves and stems was depending on the nitrate and NaCl concentration in the nutrient: Phosphorus and manganese accumulated in the leaves relative to the stem with increasing nitrate supply but magnesium and sodium accumulated more in stems than in leaves. In contrast increasing salt in the solution decreased magnesium and calcium in the leaves relatively to the stems. Increasing nitrate or salt in the solution decreased the number of live nodules on broad bean roots. Increasing nitrate concentration in the solution decreased molybdenum and phosphorus content and uptake in both legumes. The strongest effect in the experiment was observed with nitrate on molybdenum concentration and total uptake, which was reduced due to increasing nitrate supply by a factor of five. The proposed explanation for these results is that the increase in the rhizosphere pH due to nitrate uptake reduced the concentration of the species H₂MoO_4- (pK₁=4.2) and H₂PO_4- (pK₁=7.2) close to the root surface.