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Growing more food with less water - Improving water usage in agriculture

GROWING MORE FOOD WITH LESS WATER.

WATER

Expectations for the population to grow by 40 per cent to more than 9 billion by the year 2050 have raised the global question of how to grow more food with less water. With agriculture responsible for 70 per cent of all freshwater withdrawals, efficient and sustainable water use is needed for our own generation and future generations.

With our global water crisis in mind, we have created this resource to provide factual water news and information.

GREEN WATER

Green Water is also seen as a generic description for water that has been treated to a quality suitable for provision as a non-potable supply for industrial, residential or public use such as toilet flushing, horticultural/irrigation purposes, laundries, industrial processes or washing, heating/cooling functions.

GREEN WATER

Green water is the rainfall on land that does not run off or recharge the groundwater but is stored in the soil or temporarily stays on top of the soil or vegetation.

It includes soil water holding capacity and the continual replenishment of reserves by rainfall.

Eventually, this part of precipitation evaporates or transpires through plants. Green water can be made productive for crop growth. However, not all green water can be taken up by crops, because there will always be evaporation from the soil and because not all periods of the year or areas are suitable for crop growth.

Green water is the largest fresh water resource, the basis of rain-fed agriculture and all life on land.

Green water availability is calculated by the evapotranspiration of rainwater from land minus evapotranspiration from land reserved for natural vegetation and minus evapotranspiration from land that cannot be made productive.

Growing more food with less water - Green Water

GREEN WATER CREDITS

Green Water Credits (GWC) is a financial mechanism that supports upstream farmers to invest in improved green water management practices. Those farmers will benefit directly, but the benefits may not be sufficient to compensate their investments. To support these investments, a GWC fund needs to be created by downstream private and public water-use beneficiaries. Initially however, public funds may be required to bridge the gap between investments by upstream land users and the realisation of the benefits by those downstream. This pilot design, coordinated by ISRIC and supported by the International Fund for Agricultural Development (IFAD), is implemented since 2006 in Kenya and since 2008 in Morocco in close collaboration with various national institutions.

The amount of green water is determined by soil, terrain and climate, and by management.

The way that rainfall divides between infiltration and run-off is determined, in part, by soil surface attributes; some soils have a stable, porous surface structure, others crust and seal, especially when rain fall on a bare surface.

The rate of vertical and horizontal percolation of water is determined by the soil's hydraulic conductivity.

The amount of green water that may be held in the soil, or the available water capacity, depends on the volume of soil accessible to roots, its texture, structure, organic matter content and the kind of clay minerals.

Deep percolation to the groundwater may be hindered by compact layers and the lateral movement of infiltrated water to rivers is determined by the composition and architecture of unlithified materials down to the bedrock, and the shape of the soil-bedrock interface as well as the characteristics of deeper aquifers. Therefore, knowledge of about soil qualities and their spatial distribution is needed to understand the hydrological regime of both farmers' fields and river basins.

Mixed cropping, terracing and agro forestry belong to the practically feasible techniques for small scale farmers to retain 'green water' - green water is the water held in the soil as soil moisture. Green water management has proven to increase local food production, and the availability of 'blue water' for water users downstream.

Green water management in rain-fed agriculture can mitigate such land degradation.

When people refer to the Green water footprint, they are referring to the volume of rainwater consumed during the production process. This is particularly relevant for agricultural and forestry products, so products based on crops or wood, where it refers to the total rainwater evapotranspiration from fields and plantations plus the water incorporated into the harvested crop or wood.

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