What we have come to know as ‘conventional’ farming methods, use science and technology to increase yield productivity and production efficiency: genetic engineering, mechanisation, pesticides, herbicides, chemical fertilisers, tilling, and irrigation water are all examples. Conventional agriculture “treats the soil as a medium to which mineral fertilisers and chemicals are added. The soil is ploughed, tilled, cultivated, or disked two or more times a year. Herbicides clear the weeds, insect infestation is treated with pesticides, and blight or rust is sprayed with fungicides. Lack of water is compensated for with irrigation which can cause salinization of the soils.” (Hawken 2017).
Conventional, large-scale irrigation does not work anymore - actually, it never did. Proponents of industrial irrigation argue that irrigation has been used by man since early history. Indeed, there is evidence of irrigation for six thousand years in Egypt. The earth and its biospheres have existed for 4.6543 billion years. Homo sapiens have been on earth for about three hundred thousand years and only developed agriculture during the Holocene, ten thousand years ago. Up until then, humankind were hunters and gatherers. People ate what was there, in their immediate environment. It was through our transition from the Hunter/Gatherer Mesolithic to the farming Neolithic era that this greater timeline shows us the impacts of what is a decidedly “modern” farming technique. Irrigation was used, yes, making it the greatest technological invention ever created, but then it was abused and caused the downfall of several great civilisations. Lessons have been learned. Or have they? The transition from hunting and gathering to growing crops under rainfall quickly graduated to using irrigation and then to using supplemental irrigation as populations and economies grew.
The International Commission on Irrigation and Drainage (ICID) defines irrigation as “the replenishment of soil-water storage in plant root zone through methods other than natural precipitation”. And defines “supplemental irrigation” as “the addition of small amounts of water to essentially rainfed crops during times when rainfall fails to provide sufficient moisture for normal plant growth, in order to improve and stabilize yields” (ICID). Interestingly, this definition suggests that the intention of supplemental irrigation is not to increase yields but to maintain them. Clearly, the idea of increased irrigation to the extent to artificially increase yields was an irresistible next step.
Water for irrigation can be taken from surface stores such as lakes, reservoirs, and rivers, or from groundwater. These waters can be distributed via canals, dams, dikes, aqueducts, and water storage facilities. Types of irrigation range from the total flood system as is used with paddy fields, to spray, to drip irrigation, Partial Root-zone Drying (PRD), and Regulated Deficit Irrigation (RDI), where precise amounts are measured out to each individual plant, as is seen in viticulture.
Irrigation became the new technology that permitted irrigation in arid and extreme environments; an efficient coping mechanism. However, history reveals that it is not a sustainable solution, economically or ecologically. Supplemental irrigation may be the quick fix to stabilising and increasing yields, but ultimately it reduces yields because it renders the soil incapable of sustaining agriculture due to salinisation. Further, as irrigation flushes the humus out of the soil, nutrients are then replaced by chemical fertilisers, replacing the soil’s own, organic nutrients, further sending the soil hurtling towards its demise.
The real problem with irrigation is Salinisation, which occurs when groundwater levels are close to the surface. In clay soils, this may be within three metres of the surface, whereas on sandy and silty soils, it is less. Capillary forces bring water to the surface where it may be evaporated, leaving behind any soluble salts it is carrying. Salinity problems can occur under all climatic conditions and can result from both natural and human-induced actions (irrigation). Generally speaking, saline soils occur in arid and semi-arid regions where rainfall is insufficient to meet the water requirements of the crops, and leach mineral salts out of the root zone.
Salt-affected soils occupy, on a global basis, 952.2 million hectares of agricultural land. And in the world’s vineyards where irrigation is legal (the New World, and now even parts of the Old such as southern France and Spain), salinisation is the greatest threat. Speaking to producers from Australia to California’s Central Valley, the new topic is soil regeneration …. They are desperate to bring back their over-irrigated, nutrient-deleted, dead soils.
LJB, Founder, The Wine and Climate Change Institutewww.twacci.org
