While preparing for a trip to Uganda, I revisited some texts that were “required reading” when I was at university. (OK, so that was some time ago, but the principles contained therein haven’t changed!) As you can imagine, water is a premium resource in such places, and use has to be as efficient as possible. So, if you have limited amounts of water and crops growing in the field, it’s good to know when you can get maximum return on your water investment. In other words, at what time in the growing season does one get the most bang for one’s “water buck” in terms of plant response?
WHICH PERIODS OF CROP GROWTH ARE MOST RESPONSIVE TO THE WATER SUPPLY?
■ To determine the maximum yield, the grower (or crop modeller) needs to know a number of factors, including calculated maximum evapotranspiration rate, actual crop transpiration, factors that relate interactions between water supply, crop water requirements and actual yield, and the periods of crop growth that are most responsive to water supply. These vary with crop species.
For example, tomatoes produce maximum yield of high-quality fruit if provided with a controlled supply of water throughout the growing period. However, if water is limited, savings may be best made during the vegetative and ripening periods, rather than having significant yield or quality reductions when water is withheld during the other periods of transplanting/establishment, flowering and yield formation.1 Of course, in long-season hydroponic crops, flowering, yield formation and ripening all occur simultaneously and continually.
UNDERSTANDING WHEN YOU CAN GET AWAY WITH REDUCED CROP WATERING
■ For soil-grown peppers, the period at the beginning of the flowering period is the most sensitive to water shortage. Water shortage at this time reduces the number of fruit produced.
When water is in short supply, irrigation should preferably be adequate up to the first picking, and less harmful savings can be made thereafter.
The point of this is that if a combination of different crop species are being grown, and the most sensitive periods of water shortage are known for each crop, then in times of limited water supply, irrigation can be allocated to those crops that will provide better returns for this (water) investment.
The second thought comes from what’s happened in the U.K. this spring. Rather than one grower sharing the water supply differentially between crops over time, what if numerous growers (and other water users) in a geographical area would share water?
“The U.K. horticulture industry has responded to the announcement of drought status in parts of the country with a call for flexibility in sharing water resources. In the U.K., the Environment Agency (E.A.) has announced drought status in parts of the Anglian region, with areas in the South West, South East, the Midlands and Wales experiencing near-drought conditions.”2
HAVING GROWERS AND OTHER WATER USERS CO-OPERATE WITH WATER USAGE
■ Industry organizations met in June and agreed to look at flexibility in their abstraction licensing regime and to support the idea of growers joining together into water abstraction groups. In effect, growers could trade abstraction licences (or parts thereof), meaning producers and other water abstractors (such as industry and municipalities) who have water they are not using can help out other producers around them.
This could be particularly effective if combined with increases in winter storage, using floods to top up reservoirs, and better-timed irrigation of field crops. For example, “in parts of the central Fens, farmers and growers have volunteered to irrigate only at night, significantly reducing the amount of water lost to evaporation,” said E.A. representative Louise Finn.2
While the issue of abstraction licence groupings would require significant legislative changes, the fact that it is even on the discussion table highlights the need for strategic planning for water use in the U.K.
Will it really be any different here in the long term?
- Doorenbos J., et al. “Yield Response to water,” Food and Agriculture Organisation, Irrigation Paper #33.
- Tilley, J., “Growers look to share water abstraction,” Horticulture Week, Friday, June 17, 2011.