Abstract

GONCALVES, M.C. et al. Relationship between different levels of salinity and nitrogen and maize production . Rev. de Ciências Agrárias [online]. 2007, vol.30, n.1, pp.88-102. ISSN 0871-018X.

Two experimental fields in Herdade da Mitra and Alvalade do Sado, were installed in different soils, using conventional field operations. The crop was Zea Mays irrigated with a triple emitter source irrigation system. In this layout scheme there are 3 sources of water with different water quality: salty water (water source with NaCl dissolved), irrigation water+fertilizer (water source with NH4NO3 added) and irrigation water only (fresh water). With the layout it is intended to obtain two gradients: one with different levels of salinity and another with different levels of nitrogen fertilizer, in order to be able to observe the responses of soil and culture to different levels of salinity and fertilizer. The objective of this work is to evaluate if different irrigation water salinity levels can be compensated by nitrogen, and still be able to achieve acceptable crop production levels even with low quality irrigation water. In the process soil solution (EC, soluble cations and nitrates) was monitored in the groups, at 20, 40 and 60 cm depth. At the beginning, at the middle and at the end of the irrigation periods, soil samples were also collected at the four Groups and 3 depths (020cm; 20-40cm; 40-60cm) to measure soil parameters like the electrical conductivity of the soil saturation extract. Maize harvest was done in a way to evaluate the different production in the various treatments and the paper shows results related with the impact of treatments on the soil solution and crop production, and reveals tendencies of the soil salinity progression in time and the productivity of maize. Multiple regression analysis was done relating yields with the total amount of salts and nitrogen applied in the two years of the experiments (R²=0.62, n=55). The production functions obtained point to a positive effect of salinity up to nitrogen content less than 4.83 g m^-2. This useful effect of irrigation water salinity during nitrogen scarceness could be due to the replacement, and consequent availability for the crop, of the ion NH4⁺, adsorbed in the soil exchange complex, by the ion Na⁺.

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