Yield and ion content in maize irrigated with saline water in a continuous or alternating system/Produtividade e teores de ions no milho irrigado com aguas salinas de forma continua ou alternada

Irrigation with water containing salt in excess can affect crop development. However, management strategies can be used in order to reduce the impacts of salinity, providing increased efficiency in the use of good quality water. The objective of this research was to study the effects of use of high salinity water for irrigation, in continuous or cyclic manner, on vegetative growth, yield, and accumulation of ions in maize plants. Two experiments were conducted during the months from October to January of the years 2008/2009 and 2009/ 2010, in the same area, adopting a completely randomized block design with four replications. Irrigation was performed with three types of water with electrical conductivities (ECw) of 0.8 (A1), 2.25 (A2) and 4.5 (A3) dS [m.sup.-1], combined in seven treatments including the control with low salinity water (A1) throughout the crop cycle (T1). Saline waters (A2 and A3) were applied continuously (T2 and T5) or in a cyclic way, the latter being formed by six irrigations with A1 water followed by six irrigations by eitherA2 or A3 water, starting with A1 at sowing (T3 and T6) or 6 irrigations with A2 or A3 water followed by 6 irrigations with A1 water (T4 and T7). The use of low and high salinity water resulted in lower accumulation of potentially toxic ions (Na and Cl) and improvement in the Na/K balance in the shoots of maize plants. Application of saline water in a cyclic way also allows the substitution of about 50% of water of low salinity in irrigation, without negative impacts on maize yield. Key words: Zea mays L., salt tolerance, irrigation management. A irrigacao com aguas que contenham sais em excesso pode afetar de forma negativa o desenvolvimento das culturas. No entanto, estrategias de manejo devem ser utilizadas de modo a reduzir os impactos da salinidade, proporcionando aumento na eficiencia do uso de agua de boa qualidade. O objetivo deste trabalho consistiu em estudar os efeitos de uso de agua de alta salinidade na irrigacao, de forma continua ou ciclica, sobre o crescimento vegetativo, a produtividade e o acumulo de ions em plantas de milho. Foram realizados dois experimentos durante os meses de outubro a janeiro, em 2008/ 2009 e 2009/2010, na mesma area, adotando-se um delineamento experimental em blocos casualizados, com quatro repeticoes. A irrigacao foi realizada com tres tipos de agua com condutividade eletrica (CEa) de 0,8 (A1), 2,25 (A2) e 4,5 (A3) dS [m.sup.-1], combinadas em sete tratamentos, incluindo o