Salinidade e natureza catiônica da água de irrigação na morfofisiologia e produção da mamoneira.

Abstract

In semiarid areas of the Northeast of Brazil, the salt concentrations that affect the growth and development of plants vary and the effects on crops depend, among other factors, on both the concentration total and the ionic composition of water utilised in irrigation. In this context, in this study the emergence, growth, physiology, production of castor bean cv. BRS Energia and the possible impacts on soil chemical properties were evaluated. The experiment was conducted in drainage lysimeters under greenhouse conditions using an Eutrophic Ultisol of sandy loam texture, in the municipality of Campina Grande-PB, during the period from November, 2013 to February, 2014. Six water salinity combinations were studied (S1 - Control; S2 - Na+; S3 - Ca+2; S4 - Na++Ca+2; S5 - K+ and S6 - Na++Ca+2+Mg+2), in a randomized block design with four replications, each plot was composed of five plants, totaling 120 experimental units.In control (S1), the plants were irrigated with water of electrical conductivity (ECw) of 0.6 dS m-1, and the other treatments (S2, S3, S4, S5 and S6) water used was prepared with different cations, all in the chloride formand ECw of 4.5 dS m-1. During the experiment, the plants were irrigated daily and the volume of water applied was estimated by the water balance in the root zone, observing the volume applied and drained in the previous irrigation, plus a leaching fraction of 0.10. At 20 and 40 days after sowing (DAS), the growth and gas exchange was evaluated, and at 60 and 80 DAS only the growth variables were determined, and from 70 DAS started the harvest of the racemes.The emergence and growth of castor bean are more sensitive to ECw compared to the cationic nature of water, and the smallest reduction occurs in plants irrigated with water containing potassium in comparison to other types; The high concentrations of sodium in irrigation water cause greater reduction in water status resulting in severe damage to cell membrane integrity; calcium ion is the largest contributor to the osmotic adjustment in this species, as the lowest electrolyte leakage was observed in this treatment, in both the periods studied; the cationic nature of the irrigation water causes changes in photosynthetic activity of castor bean 'BRS Energia', and its effects increse with exposure time of stress; therefore increasing the efficiency of water use in plants irrigated with water containing potassium, represented one of the mechanisms of adaptation to salt stress although severe reduction in production of castor bean were observed. The adoption of leaching fraction of 0.10 was not enough to prevent soil salinization and resulted in increase in electrical conductivity of saturation extract ECes and exchangeable sodium percentage (ESP) in all treatments including control higher values being observed in treatments irrigated with water of 4.5 dS m-1 were used.