Growth and mineral nutrition of cowpea as a function of salinity and chemical composition of irrigation water

Abstract

The salt concentration that reduces cowpea growth depends on cultivars and is also affected by the chemical composition of irrigation water. The objective of this work was to evaluate the effect of salinity and chemical composition of irrigation water on plant growth and mineral nutrition of cowpea plants [Vigna unguiculata (L.) Walp.]. Plants were cultivated in plastic pots, using 22 kg of soil in a greenhouse and subjected to four different salt concentrations (0.5, 1.5, 3.0, and 4.5 dS m^-1) in irrigation water. These different salt concentrations were obtained by adding NaCl, CaCl₂.2H₂O and MgCl₂.6H₂O (A1), a mixture of chloride, sulphate, carbonates, and bi-carbonates salts (A2), or alone NaCl (A3). A completely randomized design, in a factorial arrangement (3 x 4), with five replicates was adopted. Total leaf area and fresh and dry masses of leaves, stems and roots were measured 48 days after sowing. The contents of inorganic solutes (Na, Cl, K, Ca, P, Cu, Fe, Mn, and Zn) were also determined. The salinity of irrigation water caused reduction in the biomass production and in leaf growth, but effects of the chemical composition of water on these parameters were not observed. However, the ionic composition of irrigation water affected the contents of mineral nutrients, especially the contents of Fe, Cu and Mn.