Dec 31, 2015
Agriculture assumes huge stake in future water availability

Agriculture will continue to play a major role in the use and management of the world’s water supply in future decades. What are the realistic options available for the agriculture sector to help alleviate the potential for a global water crisis exacerbated by climate change and other factors?

In order to be able to adequately feed and support the world’s growing population, the global economy needs to continue to grow. Water is critical to future growth. But according to most observers, it also can become the major limiting factor to growth, including the long-term vitality of the specialty crop agriculture sector.

Growing Blue, a group created by Veolia Water in consultation with the United Nations, Columbia University and water conservation groups, cited an International Food Policy Research Institute (IFPRI) analysis that found 4.8 billion people – more than half the world’s population – and approximately half of global grain production will be at risk due to water stress by 2050 if current behavior is followed.

The IFPRI study also found 45 percent of total Gross Domestic Product ($63 trillion) will be at risk over water stress by 2050. That’s 1.5 times the size of today’s entire global economy.

“By wasting less, polluting less, reusing more, managing effectively and becoming more efficient in all uses of water – individual, collective, agricultural and industrial – we can achieve higher water productivity levels (economic output per drop) and reduce water stress,” according to a Growing Blue report. “Continued evolution of technology and infrastructure improvements will enhance water supply capacity for cities and industries.”

According to a Growing Blue analysis, agriculture withdrawals represent 70 percent of all water withdrawals nationwide. In many developing countries, irrigation accounts for more than 90 percent of all water withdrawals. Yet in high-income countries, industry takes the greatest share of water withdrawals, with 59 percent.

“Given today’s accelerated pace of human development and the slow pace of managing issues as complex as water resources, tomorrow’s challenges are already at our door,” according to Growing Blue. “Whether improving our governance models or our infrastructure systems, years and even decades are required to implement change.”

The United Nations World Water Development Report 2015: Water for a Sustainable World, suggested that by 2050, agriculture will need to produce 60 percent more food globally and 100 percent more in developing countries.

“However, current growth rates of agricultural demands on the world’s freshwater resources are unsustainable,” stated the report, published by the Food and Agriculture Organization (FAO) of the United Nations. “Inefficient use of water for crop production depletes aquifers, reduces river flows, degrades wildlife habitats and has caused salinization of 20 percent of the global irrigated land area.”

FAO proposed five principles that should be pursued to meet the world’s water needs, including improving efficiency in the use of resources through sustainable agriculture.

“Sustainability requires direct action to conserve, protect and enhance natural resources,” FAO said. “Agriculture that fails to protect and improve rural livelihoods and social well-being is unsustainable. Enhanced resilience of people, communities and ecosystems is key to sustainable agriculture. Sustainable food and agriculture requires responsible and effective governance mechanisms.”

FAO points to two options to increase water-use efficiency: reduce water losses and increase water productivity.

The latter include the choice of genetic material and improved soil fertility and plant protection.

“It is important to note that plant breeding and biotechnology can help by increasing the harvestable parts of the biomass, reducing biomass losses through increased resistance of pests and diseases, reducing soil evaporation through vigorous early growth for fast ground cover and reduced susceptibility to drought.

“Managing overall demand through a focus on water productivity rather than concentrating on the technical efficiency of water use alone is an important consideration,” according to FAO.

FAO maintains maximum crop productivity is achieved using high-yielding varieties with optimal water supply, soil fertility and crop protection.

“Crops also can produce well with sub-optimal water supply,” FAO said. “In deficit irrigation, water supply is less than the crop’s full requirement, and mild stress allowed during growth stages that are less sensitive to moisture deficiency. The expectation is that any yield reduction will be limited, and additional benefits are gained by diverting the saved water to irrigate other crops or for other beneficial uses.”

FAO pointed to studies in India on irrigated ground nuts. Production and water productivity were increased by imposing transient soil moisture-deficit stress during the vegetative phase, 20 to 45 days after sowing.

“Water stress applied during the vegetative growth phase may have had a favorable effect on root growth, contributing to more effective water use from deeper soil horizons,” FAO said.

Higher water savings are possible in fruit trees compared to herbaceous crops, FAO said.

“In Australia, regulated deficit irrigation of fruit trees increased water productivity by approximately 60 percent, with a gain in fruit quality and no loss in yield,” FAO reported. “It should be noted, however, that deficit irrigation can only obtain good results if the irrigation systems provide very reliable water services that are also quite flexible.”

Conservation model

In the United States, the potential impact of a depleted water supply may be no more evident than in the past few years in California and other Western states, as prolonged drought conditions continue to make their mark.

One strategy for maintaining the water supply that has potential for success in the long-term may involve a practice of flooding farms in winter to help replenish water.

University of California, Davis (UC Davis) researchers are encouraged by early results from tests to see if deliberately flooding farmland in winter can replenish aquifers without harming crops or affecting drinking water.

Researchers said pears, wine grapes, many annual crops, and some varieties of almonds, peaches and plums appear best suited for on-farm flooding.

“On-farm flooding looks very promising,” said Helen Dahlke, a UC Davis professor and hydrology expert. “We’re pleasantly surprised by how quickly water tables have responded to on-farm flooding without damage to crops.”

Dahlke and her team are working with alfalfa growers in Siskiyou County and will test flooding on almonds in the Central Valley this winter, looking at plant physiology, infiltration rates, potential water quality concerns, costs and other issues. They are building on previous research in the Kings River Basin, where up to 75 percent of diverted floodwater percolated down to aquifers.

“We flooded pistachios, alfalfa hay and wine grapes,” said Don Cameron, manager of Terranova Ranch along the Kings River in Fresno County. “Our wine grapes
were under water for five months, which raised a few eyebrows, but they did fine. Diverting floodwater to farms can recharge groundwater and reduce the risk of downstream flooding. It’s a good situation all around.”

Not all soils are particularly permeable and not all crops can tolerate extra irrigation in the winter. Some soils are especially saline, and some crops need more nitrogen than others. Researchers wonder whether flooding fertilized farmland or saline soil will leach those chemicals into the groundwater. Or, could on-farm flooding actually improve groundwater quality by diluting salts and nitrates?

Professor William Horwath, a soil biochemist with the UC Davis Department of Land, Air and Water Resources, and Phillip Bachand, environmental engineer with Tetratech, in Davis, started looking at on-farm flooding at Terranova Ranch in 2010 when downstream flooding was a bigger issue than drought in California. They diverted floodwater from Kings River to various test plots and found that it recharged groundwater without hurting crops or water quality.

As the drought wears on, more researchers are taking a closer look at
the possibilities and limitations of on- farm flooding to recharge groundwater. Soil expert Anthony O’Geen, a UC Cooperative Extension specialist with
the UC Davis Department of Land, Air and Water Resources, recently concluded that some 3.6 million acres of farmland have good recharge potential because they could likely accommodate deep percolation with little risk of crop damage or groundwater contamination.

Gary Pullano, Associate Editor

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