Abstract
Cowpea is widely grown in the Brazilian semiarid region, however, due to excess salts in the soil and irrigation water constantly low crop productivity has been observed. Accumulation of salts in the soil, growth and biomass partition of cowpea under salt stress and phosphorus fertilization was evaluated in this study. The assay was conducted in a greenhouse in Mossoro, State of Rio Grande do Norte, Brazil, from September to December 2015, using a Alfissol Latosolic with low phosphorus content. The experiment was carried out in a randomized block design in a factorial 5 x 3 arrangement, consisting of five water salinity levels (0.5, 1.5, 2.5, 3.5 and 4.5 dS m-1) and three doses of superphosphate (60, 100 and 140% of the recommended dose for crop - 60 kg ha-1 of P2O5), with five repetitions. The plants of cowpea cv. Paulistinha were cultivated for 49 days after sowing in lysimeters with 8 dm3 capacity. During this period was determined the accumulation of salts in the soil, growth and biomass partition plants. Water with salinity higher than 1.5 dS m-1 increased soil salinity above the crop’s threshold of 4.9 dS m-1, 21 days after sowing. Increased salinity impaired growth and biomass partition of cowpea plants, with greater accumulation of dry matter in the leaves and stem in comparison to the root. Hinghest dose of superphosphate promoted greater growth of cowpea plants.
Highlights
Cowpea (Vigna unguiculata L.), a leguminous species with great food potential
There were variations in the electrical conductivity of the saturation extract as a function of the different periods of collection, fertilization managements, and electrical conductivity of the irrigation water used in the cultivation of cowpea plants (Figure 1A, B, and C)
During the first 14 days of cultivation, none of the water salinity levels conditioned the soil to salinity values higher than the threshold of the cowpea crop, which is 4.9 dS m-1 for the saturation extract (AYERS; WESTCOT, 1999), regardless of the studied fertilization management
Summary
Cowpea (Vigna unguiculata L.), a leguminous species with great food potential. Because of its high protein content, cowpea is an important crop, especially for developing countries (MOUSINHO; ANDRADE JUNIOR; FRIZZONE, 2008; RAMOS et al, 2012). Considering that cowpea tolerates electrical conductivity of up to 3.3 dS m-1 in the water and 4.9 dS m-1 in the soil (AYERS; WESTCOT, 1999), irrigation management strategies for the crop become necessary because of the accumulation of salts in the soil, especially in the form of sodium chloride, which can cause necrosis of leaf tissues and accelerate the senescence of mature leaves, factors that reduce the area available for photosynthesis (ESTEVES; SUZUKI, 2008; MEDEIROS et al, 2003; MUNNS; TESTER, 2008; NEVES et al, 2009; TAIZ; ZEIGER, 2013). Salt stress has three crucial effects on plants: osmotic effect, restricting water absorption by the plant, affecting growth and cell elongation; accumulation of potentially toxic ions inside the plant, causing discontinuity in the enzymatic and hormonal activity of the plants; and nutritional disorders, causing deficiency of essential nutrients, affecting the entire physiological functioning of the plant (ESTEVES; SUZUKI, 2008; MUNNS; TESTER, 2008; TAIZ; ZEIGER, 2013)
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