HIGHLIGHTS

Irrigation using water with electrical conductivity above 2.5 dS m^-1 is not adequate for ‘Paulistinha’ cowpea.

Increment in phosphorus dose does not increase phosphorus content in cowpea plant.

Under salt stress conditions, cowpea plants require lower doses of phosphorus.

Key words:
Vigna unguiculata; mineral nutrition; single superphosphate; salt stress

ABSTRACT

Soil and water salinization problems are increasingly common in arid and semi-arid regions, so it is necessary to adopt technologies that enable the use of these natural resources in agriculture, allowing satisfactory plant development. Thus, the objective of this study was to evaluate the effects of saline water irrigation associated with phosphate fertilization on soil salinity and on phytomass accumulation and nutrient concentration in cowpea plants. The study was carried out in a greenhouse using a randomized block design in a 5 x 3 factorial scheme consisting of five electrical conductivity of irrigation water electrical conductivities (0.5, 1.5, 2.5, 3.5 and 4.5 dS m^-1) and three phosphorus doses (60, 100 and 140% of the recommended dose - 60 kg P₂O₅ ha^-1), with five repetitions. Plants were cultivated in 8 dm³ lysimeters until the flowering stage and, during this period, soil salinity, phytomass accumulation and nutrient concentration in the plant tissue were evaluated. Irrigation with water with electrical conductivity above 2.5 dS m^-1 increased soil salinity and sodium concentration in the tissues to toxic levels, reducing phytomass accumulation and concentrations of macronutrients in cowpea plant tissue, except for nitrogen. Application of 60% of the recommended dose of phosphorus for cowpea improves its ionic homeostasis, increasing the absorption of potassium and calcium, but does not reduce the deleterious effects of high salinity on phytomass accumulation.

Key words:
Vigna unguiculata; mineral nutrition; single superphosphate; salt stress