The Effects of Secondary Soil Salinization :: Agriculture Agricultural Essays

Introduction: Irrigation has been used as tool by humans for over 8000 years. Irrigation started in the Nile valley where humans attempted to modify the way that the river seasonally flooded their fields in order to make cropland more productive (van Schilfgaarde, 1994). From 1940 to 1989 the amount of land being irrigated around the world has increased at a rate of 2.7% per year. In 1940 there were 95 M ha in irrigation while by 1989 there were over 280 M ha (van Schilfgaarde, 1994). This large increase in land under irrigation occurred at the same time as an exponential jump in human population, and increases in both are greatest in the arid and sub-arid regions of the Earth. Our population has therefore become reliant on irrigation to fend off large scale hunger (Abrol et al., 1988). As rain falls it carries no dissolved salts. Once this water strikes the earth and travels as surface runoff or in ground water it will come into contact with and carry dissolved salts. Any water used for irrigation carries ions in solution and by depositing this water on our fields in the form of irrigation we can effect the concentration of salts in our croplands. If these salts become too concentrated it can lead to salinization. Salinization can reduce yields in it's earliest stages and eventually lead to the destruction of fertility in the soil. Currently the Earth is losing 3 ha of arable land a minute to the effects of salinization (Abrol et al., 1988). Can we stop this loss? Will we be able continue using arid lands to meet our food needs? The Secondary Salinization Process Salinization has a direct effect on both plant growth and the structure of the soil. If the soil is saline a plant will have to expend energy bringing water into it's cells because it is forced to work against osmotic potential. The cation exchange complex (CEC) effects the stability of colloid size particles in the soil. The cation's positive charge will be attracted to the negative charge found on clay particles which make up most of the colloid fraction. Di-valiant cations(Ca, Mg) will allow the colloidal particle to get close enough together that Van Dehr Wahls forces will cause the clays to flocculate, or form stable aggregates. Sodic soils, whose CEC is dominated by mono-valiant sodium cations, will tend to be dispersed and not form stable aggregates.