Is Sustainable Agriculture with Seawater Irrigation Realistic?

Abstract

Since 1966 the use of seawater for agriculture was often studied. Despite intensive research and projects, only few organisms have been found, which can be grown with seawater: some mangrove trees and shrimps. Even today there is still no considerable use of seawater irrigation. Some halophytic vascular plants, however, can fulfil their whole lifecycle with seawater. But they also grow better on half seawater concentration. In many thousands (!) of other projects (with many cash crops) the use of only 10-20% seawater concentration has been tried. But even this concentration is often too high and spoils the soils in their structure, especially if not an efficient leaching is applied. A sustainable agriculture based on irrigation with seawater on a large scale seems to be still an utopic illusion. For special cases certainly a small scale seawater irrigation on anyhow saline coastal areas may be in fact very advisable and even economic, e.g. for production of secondary compounds, for producing fiber material, for horticultural purposes and especially for phytoreclamation of sometimes large areas of salt- and sand-deserts of desiccated seafloors (e.g. Aral Sea) etc. For saline and alkaline degraded lands only real Eu-Halophytes and Recreto-Halophytes can be used for phytomelioration. For their propagation it needs special techniques. And it needs special techniques for planting seedlings and saplings depending on site conditions. There are many applications but very few for food production. Under an arid climate sustainable agriculture with high production of crops per surface area is always only achievable with nonsaline conditions. On the long run it pays more to spend additional costs to maintain sustainable irrigation and leaching systems to keep salinity of soil low. The takehome message is: "No irrigation without drainage!" This also means it pays more to invest in good desalinization technology systems (inverse osmosis, energy sources from high radiation in deserts, photovoltaic devices etc.), to keep soils low in salt, since fresh water is always indispensable for human welfare. Basic facts and ecological principles on climate, aridity and salinity, on ecophysiological behaviour of plants to salinity and definition of halophyte-types, on salt balance in ecosystems, in soils and fields, on saline agriculture and crop yield as well as on sustainable agriculture with seawater at specific sites are discussed with the help of often-heard statements, relevant answers and take-home messages are supplied.