Saline water irrigation in semiarid region: II – effects on growth and nutritional status of onions

The use of saline waters for the irrigation of crops such as onion is a common practice in the Brazilian semiarid region. However, the effect of the use of these waters on onion nutrition and growth has been underappreciated. This work aims to evaluate Ca2+, Mg2+, Na+, K+ and Cl- levels and onion growth in two Fluvisols under irrigation with waters of variable electrical conductivity and increasing values of sodium adsorption ratio. A greenhouse experiment was conducted in two Fluvisols cultivated with onion. After transplanting each plant was irrigated with saline waters, in a factorial arrangement 2 x 3 x 6, corresponding to two soils (sandy loam and silt clay loam), three values of electrical conductivity (EC - 200, 700 and 2,000 μS cm-1) and six levels of sodium adsorption ratio (SAR - 0, 5, 10, 15, 20 and 25 (mmolc L-1)0.5). Plants were collected at 90 days after transplanting and onion growth parameters as well Ca, Mg, K, Na and Cl levels were each measured. The SAR of the irrigation waters and the soil did not show any significant influence on the onion growth variables or on the levels of the evaluated elements. The increase in salinity of the irrigation water promoted a reduction in the growth variables of the evaluated onion cultivar. Increases in the levels of Ca, Na and Cl as well as a reduction in the level of K in the onion plant dry matter were all observed with increasing salinity of the irrigation water; however, the Mg content level was not affected. As the salinity of the irrigation water was the main factor affecting onion growth, an EC of 200 µS cm-1 is the limit to promote the best onion growth cultivated in both sandy and silt clay soils.