CHAPTER 2. BACKGROUND
2.4 WATER USE AND MANAGEMENT BY COMMODITY
Compared to the rest of Canada, especially the Prairies, in Central Canada, a relatively small percentage of water resources are allocated for irrigation purposes. While the water extracted for agricultural purposes is not significant, it still represents the third largest water consumer in Ontario accounting for 20% of total provincial consumption. Municipal water supply is Ontario’s top user, accounting for 38% of the total consumption, followed by the manufacturing sector (28%).
In Ontario 76% of the water extracted for agricultural use is consumed, meaning that this water is not returned to the source (De Loë et al., 2001). Across this area, for most part of the year, the rainfall received exceeds evapotranspiration. However, throughout the summer months of June, July and August, irrigation is generally required.
In Ontario, irrigation is mainly used for high value horticultural products, such as vegetable and fruit production. In Southern Ontario 43% of cultivated land is under irrigation, out of which 36% under vegetable production and 14% is under fruit production (Statistics Canada, 2011). Water sources for irrigation vary across the region. On-farm water sources can be rivers, ponds, dugouts or wells. In Ontario, producers rely mostly on on-farm water resources (i.e., ponds, reservoirs accumulating precipitations or fed from the municipal water ditches, etc.), since they fulfill 83% of their water needs. Of this total, 69% is obtained from surface water sources, while the remaining 14% from groundwater sources. Farmers supplement these on-farm sources with water from off-farm sources, such as municipal water, or water transported by a canal system or vehicle (Statistics Canada, 2013).
Irrigation technologies can be grouped into three broad categories: sprinklers (high and low velocity/volumes), micro (surface and subsurface drip), and surface irrigation (flood). In Ontario, the predominant technologies used are sprinklers, accounting for 70% of the irrigated area, followed by micro technologies that represent approximately 21% of the total irrigated area. The total area under irrigation in Ontario is 28,960 ha, with 1,045 farms using irrigation. Horticultural
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producers – fruits and vegetables producers (Statistics Canada, 2013) use most of the latter technologies.
Irrigation scheduling based on plants' water needs is crucial for optimal plant growth but also for water conservation purposes. In a survey of 34 southwestern Ontario irrigators, results provided by Dolan et al. (2000) results suggested that most of the respondents’ schedule irrigation based on water needs, mostly assessed by measuring rainfall and soil moisture levels. However, Bernier (2008) notes that producers rely predominantly on their own experience to trigger irrigation, using the "feel and appearance" technique. Evidence suggests that this irrigation practice generally leads to an overestimation of water needs.
2.4.2 Water Use in Cranberry Production
Availability of water represents a critical factor in cranberry production. Irrigation in cranberry production serves multiple purposes. It can fulfill additional water requirements for the plant, alleviate heat stress, and provide frost protection. Beyond irrigation, water is also used for flooding during the harvesting stage and for protecting the plant over the winter. The cranberry growing season averages 150 days, during which time, average water requirements are 62 mm per month, with peak requirements of 102 mm/month under extreme conditions (Caron, 2009).
As the Centre-du-Québec, the region where cranberry production is concentrated, receives at least 95 mm in July – the driest month, irrigation is necessary. In addition to irrigation, water is used for flooding at the beginning of winter, in early spring, and for harvest. The cranberry basin or cultivation beds are flooded with water, reaching depths between 30 to 40 cm. Cranberry production is water intensive, it was estimated that on a yearly basis it requires 15,000 to 25,000 l/ha (Eck, 1976). However, not all water used is consumed. It was estimated that over half of it is recycled and reused or released back into the original water body.
Growers require a water reservoir with the capacity of at least 5,000 cubic meters per hectare, in order to meet their production needs (Caron, 2009 cited in Poirier, 2010). In Centre-du- Québec, growers depend on rainfall and snowmelt to refill their reservoirs. In addition to natural recharge, they pump water from the nearby surface water source, the Becancour River.
Water management in cranberry production is complex and relies on a diversity of technologies and practices. In cranberry production, drainage management and water table depth are closely linked to management of irrigation (Sandler et al., 2004). Most growers use a sprinkler
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system for irrigation purposes. The nozzles are located within the cranberry beds, a few centimetres above the ground, between 15 and 18 meters apart (Pelletier et al., 2015). Water travels from the reservoir – usually located at higher elevation on the farm, into the field by making use of gravitational force. While gravity moves the water from the main reservoir to the cranberry bed requiring irrigation, the sprinkler system receives water with the use of irrigation pumps.
Another method of irrigation used by cranberry growers is sub-irrigation. Sub-irrigation is a dual-purpose water management system that provides both irrigation and drainage. Additional water can be supplied through the same pipes that are used for drainage. The water table depth is regulated with the use of control structures. To maintain an appropriate water table depth, water is supplied under the surface, to provide ideal moisture conditions in the effective root-zone (Handyside, 2003). During the growing season and especially after heavy rain events, the drainage system becomes a very important component of the water management system.
Irrigated plots are also equipped with drains, good drainage of the cultivated beds helps prevent fungal development, salinity issues and decreased yields. Drainage is also used to lower the water table during spring snowmelt and after harvest. This is realized with subsurface drains and surface ditches available under and along each field (Roper and Vorsa, 1997). To manage water resources, some growers use tensiometers, which is a tool used to indicate the water available to the plant in the soil.
2.4.3 Water Use in Onion Production
Southern Québec is a humid region. The average annual rainfall is 760 mm. However, with rainfall events unevenly distributed, water can become a limiting factor at critical stages of plant development. Therefore, onion growers increasingly rely on supplemental irrigation to meet the plant water requirements. Based on experts’ estimations, currently there are between 10-35% of onion growers who irrigate across Québec (LeBlanc and Turgeon, personal communication, February 19, 2016). Due to the shallow root system, onions are sensitive to water availability. Water becomes a critical factor at certain stages in onion production. For example, a lack of water at the vegetative stage can delay the bulbing, whereas insufficient water during the bulbing stage can affect the size of the bulb (LeBlanc, 2004). In sandy soils (found in Lanaudière, Capitale Nationale), producers need to irrigate to obtain good quality and yield. In organic soils (found in Montérégie), due to the higher capacity of the soil to retain moisture, the need for irrigation is less
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frequent, and thus it is less likely for growers to irrigate onions (LeBlanc, personal communication, January 26, 2016). In terms of water sources for irrigation, onion growers in Québec use a combination of sources, predominantly groundwater and on-farm reservoirs. Where irrigation takes place, most growers rely on the feel and appearance technique, when deploying irrigation (Leblanc and Turgeon, personal communication, February 19, 2016). The “feel and appearance” technique is a qualitative way of assessing soil humidity, by which the farmer uses a handful of soil to determine approximate soil humidity.