<p>As the world population continues to grow, it will be
challenging to manage resources, reduce environmental pollution and maintain
growing demand for food production. Controlled environment agriculture (CEA) is a novel solution to reduce freshwater use
in agriculture, minimize environmental pollution from agriculture sector, and
meet the growing food demand. CEA allows for the year-round cultivation in inhospitable
climatic conditions. Hydroponics is a common method of growing crops in CEA,
where plants grow in a solution enriched with nutrients and oxygen. The
technique significantly reduces water use and fertilizer run-off during
production. In the United States, lettuce is one of the most important crops
grown using hydroponics.</p>
<p> Hydroponic
production uses several methods to grow lettuce including nutrient film
technique (NFT) and constant flood table (CFT). Moreover, several cultivars of lettuce are
grown in the Midwest. There is a lack of knowledge on whether optimal
fertilizer concentrations change depending on the cultivar or hydroponic
production system. Little information is known about the suitability of a cultivar
to a specific method of hydroponic production. For year-round lettuce
production in hydroponics, supplemental lighting (SL) and heating are required in the Midwestern
regions of the U.S. The energy requirements for SL and heating can be too
costly in winter for some growers to produce crop year-round. In addition to
light quantity, spectral composition of light can impact growth. Heating the
root zone to produce a micro-climate may be more efficient than heating the entire
greenhouse and possibly reduce overall heating costs. However, information on
spectral composition of light and the efficacy of root zone heating is unclear,
at best. Certain cultivars that can tolerate cold stress can be more suitable
in the U.S. Midwest during winter. Lettuce cultivar screening for yield under
cooler environments is limited. </p>
<p> A
completely customizable hydroponic production system that can aid in conducting
research related to above-mentioned issues was built as a part of my Master of
Science program. Using this system, 24 popular cultivars from four lettuce
groups were evaluated for productivity during summer/fall under different
concentrations of fertilizer solution, and in two production methods including
NFT and CFT during spring. In addition, yield of all 24 cultivars were
evaluated under 10, 15.5 and 21.1 °C
in a growth chamber. The eight best performing cultivars from the summer/fall trial
were evaluated during the winter in a greenhouse with the addition of SL and
root zone heating with minimal ambient air heating. </p>
<p> Results
indicated that the lowest level of electrical conductivity (EC) of the fertilizer solution used (1.3 dS·m<sup>-1</sup>) resulted
in highest yield, regardless of cultivar or method of production. Among the 24 cultivars;
Red Sails (Leaf), Salvius
(Romaine), Cedar (Oakleaf), and Adriana (Butterhead) had the highest yields
among each group during summer. Growth chamber study indicated that
Dragoon, Adriana, New Fire Red and Red Sails cultivars had higher yields than
other cultivars under cooler (10 and 15.5 °C) air temperature conditions. In the winter study,
lettuce cultivars did not reach harvestable size even after 40 days of growth
without SL and root zone heating. Supplemental light composition significantly
affected lettuce growth with higher yield under Purple (with higher proportion
of red) than White LED lighting. Commercially acceptable lettuce could be
produced using root zone heating. In general, plants grown under CFT yielded
higher than those grown under NFT in the winter trial. Among the cultivars,
Salvius, Black Seeded Simpson, Cedar, and Red Sails performed better under SL
and root zone heating during winter.</p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/11323364 |
| Date | 05 December 2019 |
| Creators | Alexander G Miller (8085998) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/Optimization_of_Greenhouse_Hydroponic_Lettuce_Production/11323364 |
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