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Inside View: August 2009

Each August, Greenhouse Canada usually has water/irrigation as its
theme, and my column looked at this a couple of years ago with respect
to practical things that growers can do to reduce water consumption
(drip irrigation, blending, pot covers for example).

Each August, Greenhouse Canada usually has water/irrigation as its theme, and my column looked at this a couple of years ago with respect to practical things that growers can do to reduce water consumption (drip irrigation, blending, pot covers for example). Last year, Inside View offered up other “green” solutions, such as building green roofs, landscape swales and stormwater planters. But here’s the scale of this water issue for growers (taken from Water Year1):

• Globally, 69 per cent of all available freshwater is used for agriculture.
• In Africa, agriculture consumes 88 per cent of all water taken for human use.
• In Europe, most water is used in industry (54 per cent), while agricultural uses take 33 per cent.
• 1,000 tons of water are needed to produce just one ton of grain.
• Pasture and crops take up 37 per cent of the world’s land area.

FRESH WATER AVAILABILITY JUST A DROP IN THE OCEAN
Think of it another way. Some 70 per cent of the Earth’s surface is covered with water, but of that, only 2.5 per cent is fresh water, and of that, only one per cent is available to humans. In other words, it’s just a drop in the ocean.
The “GreenSys 2009” conference was hosted mid-June in Québec City. Martine Dorais and André Gosselin did a fantastic job as co-chairs of an organizing committee that brought together 500 delegates from 32 countries to enjoy almost 200 oral presentations and 143 posters over four days of joint scientific and technical programs.

Especially impressive was the number of presentations that reported water use/conservation as a key finding of their work, striking in that these were high-tech topics in developed nations where we often take water for granted. High-tech meaning intensive horticulture (glasshouse) systems that many already consider to be very water efficient.

SAMPLING SOME GREENSYS ENGINEERING SOLUTIONS
But beyond obvious opportunities of reducing water needs related to direct water application, here’s a few potential opportunities from an engineering perspective:

Mike Parrella (U.C. Davis)  looked at “Worldwide Development of Sustainable Production Systems in Greenhouses,” concluding that while we might need more greenhouses (especially like that of the new Houweling facility in Camarillo) to feed an increasing population, water is an increasingly critical issue. Indeed, many nursery growers in California are being restricted to watering but once per week resulting in numerous business closures.

Ariane Grisey (CTIFL France) looked at results of a geothermal greenhouse project. As well as expected results, such as a 21 per cent energy saving, Grisey highlighted a 41 per cent saving in water. This is significant in that reporting this would probably not have happened a decade ago.

Peter Klapwik (GreenQ, the Netherlands) discussed the potential for closed greenhouses in North America by looking at a trial greenhouse in the Netherlands. Growing tomatoes (inter-planted twice) over a period of 26 months, the crop yielded 200kg/m2 and in so doing used 20 per cent less water in 2008 (than a conventional crop). Peter also reported on aquaponic trials that make more efficient use of water by producing both greenhouse vegetables and edible fish.

Murat Kacira (University of Arizona) outlined the major needs for developing sustainable greenhouses, identifying water saving as one of these, and discussed capturing and reusing the water that is transpired by a crop into the greenhouse air.

Anja Dieleman (WUR, Wageningen, the Netherlands) presented a keynote speech entitled, “Energy Saving: From Engineering to Crop Management.” In so doing, she challenged conventional Dutch wisdom that increased transpiration means “active crops” and subsequent optimum yield. Dieleman found that leaf removal in peppers to about half of the normal leaf area index in August gave eight per cent energy savings without a yield penalty. Less transpiration requires less energy to maintain suitable greenhouse humidity.

 Clearly, reduced transpiration could lead to significant water savings.

Carlo Bibbiani (University of Pisa, Italy) presented some ideas that, while a way off from commercial application, offer potential for using photovoltaic panels to provide energy supply and water recovery from greenhouses by night radiation.

There’s a long ways to go to make the most use out of our “1 per cent of 2.5 per cent of 70 per cent,” but obviously many people are working hard to reduce the significant demands of agriculture’s share.
1           www.wateryear2003.org/en