One problem that concerns most maize researchers in northern climates is how to obtain adequate numbers of well-developed plants on a year-round basis. For some plant species that do not require intense light, standard greenhouses usually suffice. For others that require summer-like light intensities for normal development, supplemental lighting in a greenhouse is the usual manner of improving light quality and quantity. We have taken a different approach to solving this problem by constructing a large indoor growth room in which corn is capable of growing to maturity.
The dimensions of the growth room are 24 feet by 38 feet with a ceiling height of 19 feet. The floor is concrete with four floor drains. The two exterior walls are concrete block and the interior walls are covered with sheet-rock. The ceiling is corrugated steel. An epoxy paint was applied to waterproof the walls. There is a working area with sink and appropriately spaced water spigots for watering.
In order to provide adequate light intensity and quality, the growth room was outfitted with twenty-three 1,000 watt high pressure sodium (HPS) lamps and twenty-two 1,000 watt metal halide (MH) lamps. These lamps provided not only the intensity necessary, but when placed alternately, gave a very good spectral mix. The different lights are alternated within a row as well as between adjacent rows (i.e., one row starts with an HPS, the next with an MH). The spacing is four feet on center within a row and three feet on center between rows. This spacing was chosen to facilitate a blending of the light from the different lamps. The MH lamps are richer in the blue region of the visible spectrum (around 450 nm). The HPS lamps are rich in the red and far red region, especially around 550-600 nm. The plants are on a 14-hour light, 10-hour dark cycle. The ballasts for the lamps are mounted on a metal framework 12 feet from the floor. The reflectors are attached to the ballasts with a power cord that allows them to be moved via a pulley system. The height available for plant growth is 10-11 feet.
Temperature control is accomplished with two units (one is an air conditioner and the other is a combination air conditioner/heater) that have a total cooling capacity of 181,000 BTU/hr and air movement of 6,000 CFM. The ventilation system for this room is independent from that for the rest of the building. Plastic convection tubing (usually used in greenhouses for good heat distribution) is being used to assure effective air distribution and temperature control. The air conditioners are controlled by a remote sensor that is mobile and can be placed where desired in the plant canopy. The temperatures maintained are 66 F at night and 80 F during the day.
The soil mix used is a 1:1:3 (soil:sand:peat) that is mixed 3:1 with perlite. After the plants reach the four leaf stage they are fertilized once a week with 20-20-20 fertilizer (30 g/liter) and a soluble trace element mixture (25 mg/liter). This is applied with a 1:15 proportioner, with each pot receiving approximately 1,200 ml of the solution. The plants are grown in three gallon pots.
We have had good success growing many public inbred lines, as well as some special stocks. One line, W22 R-nj, which can be difficult to self in a winter greenhouse environment, has been grown and selfed successfully in our growth room. Plants are routinely selfed, except for a few lines where silking and pollen shed do not allow proper nicking. A high degree of prolificacy has also been observed among plants grown. The plants mature properly in all respects, and resulting ears have good seed development. Typically, ears are harvested five to six weeks after pollination. This continuous supply of plants has allowed us to make considerable headway in our corn tissue culture program.
Additional information is available from us upon request.
D. A. Kremer, C. E. Green and J. C. Woodman
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