Evaluating the Efficiency of Wicking Bed Irrigation Systems for Small-Scale Urban Agriculture

Abstract

A wicking bed (WB) is a plant driven system where plants receive water through capillary rise from a self-contained coarse material-filled subsoil reservoir. WBs have been widely promoted as a water-efficient irrigation solution for small-scale and urban food gardens. However, little published research exists to support popular claims about their effectiveness. In this study, the performance of WBs was compared with best-practice, precision surface irrigation in terms of water use efficiency (WUE), fruit yield, fruit quality and labour input, using tomato (Solanum lycopersicum) as the experimental crop. The influence of WB design variables (reservoir depths and soil bed depths) was tested. Results showed that WBs performed as well or better than precision surface irrigated pots, showing statistically significant improvement in WUE, yield and fruit quality. The results also suggest an optimum design exists for soil depth (where 300 mm outperformed 600 mm) but not reservoir depth (no difference between 150 and 300 mm). The WBs were more labour efficient, requiring significantly less frequent watering to achieve the same or better WUE. WBs are inherently low-tech and scalable and appear well-suited to a variety of urban agriculture settings.Horticulturae 2016, 2, 13 2 of 18 to rural water supplies for commercial horticulture [14,15]. There is therefore a great interest in the development of efficient irrigation systems which can secure urban water resources and provide urban gardeners with an economically efficient means of irrigation that is not technologically complex [16][17][18].Although improved practices exist for efficient crop irrigation in commercial farm management, there has been limited adoption of these techniques in urban areas due to the barriers of cost and knowledge to maintain them [18]. In urban gardens, the issues principally revolve around determining when and how much water needs to be applied to crops. For example, precision irrigation scheduling has been widely applied for efficient irrigation of large-scale monoculture crops. At the domestic and community garden scale, however, plants tend to be mixed and irrigation cannot be optimally scheduled to meet the needs of multiple crop water use patterns [19,20]. As a result, homeowners frequently apply more water than necessary, which leads to water loss as subsoil drainage [21]. Another major problem for urban growers is the labour invested in watering which may conflict with other activities [22]. In some regions, those interested in growing crops are not able to do so due to the presence of legacy contamination [23] or a shallow water table [24].Capillary wick irrigation has been investigated for some years as a method to deliver water to plants in container gardens [25]. Existing approaches include wicking mats, self-watering pots, and sub-irrigated planters [24,26]. The more recent "wicking bed" (WB) [27] has been characterized by a saturated media-filled reservoir beneath an unsaturated soil (root zone). Water is delivered by capillary acti...

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“…Whereas the most dominant two frequencies were daily and then weekly for bed-mixed (46%; 31%) and for raised-mixed (50%; 40%). This finding supports the only other published scientific research on wicking beds, by Semananda et al [38], who found wicking beds to be significantly more labour efficient than precision surface irrigation. While growing seedlings, their experimental wicking beds could go up to 4 weeks without irrigation, and with mature tomato plants could go 1-2 weeks without irrigation [38].…”

Evaluation of Deficit Irrigation and Water Quality on Production and Water Productivity of Tomato in Greenhouse

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“…Contact between water surface and growing substrate ensures water availability within the rhizosphere due to upward water movement associated with hydrophilic nature of the growing substrate. This system is using similar principle to wicking hydroponic system (Datta, 2015;Semananda et al, 2016). Garcia and Mendoza (2008) reported that high soil or substrate water content increased shoot growth, but excessive water condition could limit root growth.…”