Effects of acid soil infertility factors on mineral composition of soybean and cowpea tops

Abstract

Investigations on the effects of acid soil infertility factors on legumes are often focussed on growth, nodulation, and N₂‐fixation, while very little emphasis has been given to the mineral composition of plants. In the present investigation, effects of varying solution pH [4.5, 5.0 and 5.5], concentrations of Ca [0.05, 0.5 and 2.5 mM] and activities of Al [0 ‐ 33 μM] on chemical composition of the tops of soybean [Glycine max (L.) Merr. cv. Fitzroy] and cowpea [Vigna unguiculata (L.) Walp. cv. Vita 4] plants grown in dilute nutrient solutions were examined.

An increase in solution pH significantly increased concentrations of N, K, Ca, Mn, and Zn in soybean tops and concentrations of only K and Mn in cowpea tops. An increase in solution Ca concentration increased concentrations of Ca and Cu, and decreased concentrations of Mg, Mn, and Zn in both soybean and cowpea tops. The concentration of Al in soybean and cowpea tops was greater in plants grown in solutions containing a sum ofactivities of monomeric Al species [Sa_{Al mono}] of 6.5 μM than that in plants grown in solutions containing no Al. Further increase in Sa_{Al mono} in solutions decreased Al concentration in soybean tops, but not in cowpea tops. An increase in Sa_{A1 mono} in solutions decreased the concentrations of N, P, K, Ca, Mg, Mn, Zn and Cu in soybean and cowpea tops. However, the Sa_{Al mono} at which concentrations of each of the essential elements in plant tops decreased significantly were different for soybean and cowpea.