Difference between revisions of "Fundamental resources/Water/Water-efficient agriculture"

Revision as of 18:10, 17 June 2011

"We need a 'Blue Revolution' in agriculture that focuses on increasing productivity per unit of water — more 'crop per drop'.

70% of world water use goes to irrigation for agriculture. The single most important thing we can do if we want to reduce water demand is to increase the water-efficiency of agriculture. Along with protecting the environment and securing food supplies, this is a third reason to move to sustainable agriculture, which consistently effects large reductions in water used ^[1]. The various types of food-production suggested in the Food article are all very economical with water. There are several very simple ways to reduce agricultural water use —

• Permaculture designs generally avoid leaving earth bare. The ground is covered either with plants such as clover and grass, or with mulch such as straw or woodchips. When ground is covered, water does not easily evaporate from it. This method reduces water requirements 25-50%.
• Soil infiltration is the amount of water soil can hold. The higher the soil infiltration, the less water need be applied. No-till farming , which is gaining popularity around the world, dramatically increases infiltration while reducing labor and increasing yields.
• Compost, the basic fertilizer of sustainable farming, increase soil infiltration 125%^[2]
• Mob-grazing (a method of raising livestock that emulates natural grazing patterns), has been shown to increase infiltration as much as 775%^[3]
• Agroforestry (the practice of planting trees between crops), which is a key aspect of agroecology, significantly increases infiltration and reduces water use. In addition, trees have much deeper roots than food crops, so they can draw up deep groundwater and bring it into the field. The shade provided by the trees also reduces evaporation by two-thirds ^[4]
• Ancient peoples living in dry places devised some ingenious systems to catch what little rainwater they had and use it to grow plants. This is exemplified in the area around Syria and Jordan, where there are productive rainfed farms in areas with as little as 120mm of rainfall per year. Very simple earthworks can turn arid areas into productive farm. These include stone walls built on contour to stop water draining downhill, hollows dug into the ground to accumulate rainwater, swales, which are a combination of these two methods, and mini-dams to redirect ware towards productive areas. A combination of agroforestry and earthworks can make any area productive, as has recently been demonstrated in Burkina Faso, Niger

Swales are a simple and effective rainwater harvesting method that can be used anywhere. Without swales, rainfall runs off the hillside. When a series of swales, long depressions with an earthen wall on the downhill side, are dug, the rainfall cannot run off. It pools in the swales and gradually soaks into the soil. In this way, a single rainfall can provide moisture that can be used by plants and trees for months or even years.

• Currently, the most commonly used method of irrigation is the most inefficient: flood irrigation. 95% of all irrigation worldwide is done by this method^[5]. Drip and sprinkler irrigation can be used instead of flood irrigation. Drip irrigation is about 95% efficient ^[6][7], compared to about 50% for flood irrigation^[8]. If all the world's flood irrigation systems were replaced with drip irrigation, world water usage would be reduced by 29%. The main barrier to implementing drip irrigation is a lack of proper equipment: but the trend towards distributed digital manufacturing will allow anyone to easily fabricate sprinklers, pumps, controllers and supply systems appropriate to their local needs.
• Aeroponics uses a tiny fraction of the water of drip irrigation. It is by far the most water-efficient means of growing food yet devised.
• Seawater agriculture can grow food in coastal regions, requiring no fresh water at all.
• Aquaponics recycles the same water over and over, so that a given amount of plants can be grown in only 10% of the water a garden would need.
• Water-efficient varieties of crops can be grown in water-scarce areas. It is now possible to rapidly determine the water-efficiency of plants by measuring their carbon isotope discrimination. This means multiple varities of a given plant can be grown in controlled conditions and compared for water-efficiency. The most efficient can then be cross-bred and spread around the world.
• Large-scale atmospheric water condensers can readily be used to generate significant amounts of water from the air on farms.

A combination of these techniques — applied intelligently and with a sensitivity to local needs and resources — can enable even rather dry climates to secure their own food supply without the need to pump in water from elsewhere. Rainfed agriculture currently provides about 60% of the world's food ^[9]. This could be expanded to nearly 100% using the methods mentioned here, while we can also make irrigation at least twice as efficient. This would massively unburden the world's water needs.

The recent tragic famines in Niger, Sudan and Chad have been blamed on droughts, but they have more complex causes than a simple lack of rain. While drought was the immediate cause of the crop failure, the drought would not have done the same damage to an agricultural system that used water more effectively. By building soil infiltration and using groundcover and trees, we can build agricultural systems that are resistant to drought and put an end to catastrophic crop failures.