A: Approximately 12,000 gallons.
Closed-loop irrigation systems have been shown to achieve significant increases in water resource efficiency. Commercial lettuce production guidelines published by the University of Hawaii, for example, suggest that optimal field irrigation rates for head and leafy lettuce varieties require the application of .6 gallons per ft2
per week (1 inch/acre/week) in humid climates.1
Closed-loop hydroponic systems growing lettuce crops have exhibited water use efficiency gains of 60% and greater as compared to irrigation rates of open field cultivation.2
Other crops have exhibited a range of efficiency gains when grown in closed-loop systems. A study conducted in Jordan on hydroponic production of forage crops (i.e. peas, barley, wheatgrass) resulted in efficiency gains of over 95%3
while an Australian study documented a 33% increase in water efficiency for hydroponic cucumber production.4
Closed-loop irrigation methods have also achieved large gains in fertilizer use efficiency. Commercial guidance published by the University of Arizona recommends the application of 175-200 lbs. of nitrogen per acre per season for lettuce crops as an example. However, that same guidance projects that as much as 50% of that nitrogen will be lost to run-off during the growing season.5
Comparatively, a scientific study examining nitrogen use in lettuce production utilizing closed loop techniques reported as much as a 75% gain in nitrogen use efficiency over field production methods.6
The actual gains in water and fertilizer gains that can be realized by a Cityblooms micro-farm are not yet known and we are looking forward to analyzing the data gathered during the trial. It is expected that resource efficiency gains realized will be in line with results documented by the scientific community. Using these metrics, a 16 unit Cityblooms micro-farm under lettuce production would realize an annual water savings of 12,160 gallons as compared to a similar area under field cultivation.
1. Valenzuela, Kratky, and Cho, Lettuce Production Guidelines for Hawaii, CTAHR, University of Hawaii. http://www.extento.hawaii.edu/kbase/reports/lettuce_prod.htm.↩
2. Monaghan, Wood, and Hilton, Improved Efficiency of Nutrient and Water use for High Quality Field Vegetable Production using Fertigation. Acta Horticulture (2010), Vol.852 . pp. 145-152. ISSN 0567-7572↩
3. Al-Karaki and Al-Hashimi, Green Fodder Production and Water Use Efficiency of Some Forage Crops under Hydroponic Conditions, ISRN Agronomy (2012).↩
4. Grewal, Maheshwari, and Parks, Water and Nutrient Use Efficiency of a Low-Cost Hydroponic Greenhouse for a Cucumber Crop: An Australian Case Study, Journal of Agricultural Water Management, volume 98, issue 5 (March 2011).↩
6. See note 2.↩