INFLUENCE OF WATER QUALITY AND IRRIGATION REGIME ON MAIZE PRODUCTION

Many irrigated areas of the Mediterranean such as Apulia region have problems of high salinity of the irrigation water with a negative impact on soil fertility and on production. To limit these effects is necessary to minimize the supply of salt and promote leaching, using an adequate irrigation management, which may vary according to climatic conditions, soil type and crop management. Yield results related to a two years trial of a grain maize crop, irrigated with furrow method and included in a four-year rotation (maize, sunflower, maize, wheat), are reported. This activity was carried out in Apulia, on a shallow red soil, resting on fissured calcareous rock, as part of multi-year research, with the aim to evaluate the influence of water quality and irrigation regime on the production of some crops and the possibility that the rain water could leach solutes brought with irrigation water. Ten treatments, resulting from the factorial combination of two types of water (fresh water with electrical conductivity-ECw- of 1.2 dS m-1 and brackish water with ECw of 5 dS m-1) have been compared, with the following seasonal irrigation regimes: i) 75% of the maximum crop evapotranspiration (ETc); ii) 100% of ETc; iii) 100% of ETc, plus 50% of the needs of leaching (LR), calculated as: LR = ECw / (5 ECe - ECw), where ECw = electrical conductivity of irrigation water (dS m-1); ECe = electrical conductivity of the saturated extract of the soil; iv) 100% of ETc, plus 100% of LR, calculated as previously indicated; v) 100% of ETc until flowering, and 75% of ETc until the end of the crop cycle. It was adopted a split plot experimental design with four replications. Irrigation was performed when in the treatment irrigated at 100% of ETc, the matric potential of the water in the layer of soil explored by the roots was equal to 0.1 MPa, providing the irrigation volume necessary to bring the matric potential to -0.03 MPa. In the first year there was no difference of corn production attributable to the water quality; in the second year, however, due to the accumulation of solutes in the soil for three consecutive seasons, the yield of grain obtained in the plots irrigated with brackish water, compared to those obtained in the plots irrigated with fresh water, have been reduced by 33.3 % (6.8 vs 10.2 t ha-1). Moving from the lower irrigation volume, to the most abundant (seasonal volume of irrigation sufficient to satisfy, respectively, 75% and 100% of ETc, plus 100% of LR), as average of the two years, the yield of grain increased from 7.4 to 9.1 t ha-1.