Thursday, February 15, 2007

Back to Basics with Seeds and Seedlings

The exterior work on the two additional greenhouses is nearing completion, so this is the time to make choices in terms of the interior work that needs to be done. Chuck and I keep referencing Dr. Louis Albright of the Cornell University Controlled Environment Agriculture (CEA) experiments.

Dr. Albright did some experiments with a CO2 generator in a lettuce growing facility and found that when the extra heat produced by the unit kicked in the ventilation system to cool things down, much of the CO2 escaped through the vents.

He recommended a closed system, cooled by an air conditioning unit, rather than venting to the outside, in order to keep the much needed CO2 in the greenhouse. I proposed this to Chuck for both of our new facilities, but he balked.

He priced the most popular air conditioning systems and found them to be too costly. I, however, urged him to do more calculations. He should take the cost of the CO2 generating unit as well as the speeded up growth rate of the crops into account, before making his decision.

Following the model of the Cornell experiments, we plan to grow Brassica campestris L., cv Hypro, which is a type of pak choi that produces plants that weigh a pound each. Using CO2 regularly during the growth process, the lifecycle of this plant can be shortened to 35 days, from seed to harvest.

Seed germination takes place in a separate room of the greenhouse, where the temperature is set at 20º C (68º F). We use trays with plastic humidity covers and one inch rockwool cubes to hold each seed. Since we plan to produce 600 heads of pak choi per day—in order to compensate for losses, we use 14 trays that fit 50 cubes each tray.

The trays have drainage holes on the bottom and are immersed in an ebb and flow hydroponic apparatus. The trays are submerged in pure water for a 15 minute period, every 12 hours.

For the first 24 hours lighting is maintained at 50 micromoles per square meter and left on for the entire 24 hours. This will help germination immensely. The humidity covers make sure that the growing medium never dries out.

The day after a half-strength fertilizer solution is added to the germination system. In our case, this is Advanced Nutrients Micro and Grow, without the Bloom. The pH of the solution is adjusted to 5.8, using a small quantity of pH Down, since the pH of pure water is usually neutral, around 7.0.

The temperature of the germination room is raised to 25º C at this point and the light intensity is increased to 250 micromoles per square meter. These are the settings that the computer controlled environmental system maintains for the rest of the germination period for the pak choi.

On day 3 the humidity covers are removed—the seeds should have germinated and the radicle has penetrated into the grow medium. The high humidity levels for the first two days are necessary to make sure the seed doesn’t dehydrate. This is also the reason for starting with a low light level.

Possible double seedlings should be removed on Days 4 and 5 to ensure the uniformity of the pak choi crop. The uniform environmental conditions and growth progress are essential if a consistently uniform pak choi crop is to be produced.

Day 6 is set aside for seedling selection. Depending on the size and expansion of their first true leaf, only those that have reached at least 1 cm in diameter are allowed to continue. About twenty percent of the seedlings will be discarded at this stage.

On Day 7 the watering frequency is increased, since the seedlings have grown to a size that requires more water and nutrition. The system is adjusted to flood the grow medium in the trays four times per day for 15 minute periods each time.

The roots of the seedlings are sticking out on the bottom of the cubes. At this time, we hand dip each seedling into a mild solution of Voodoo Juice and add B-52, an excellent vitamin supplement to the nutrient mix.

On Day 10, the seedlings are ready for transplanting. Since this process usually involves some stress, we will use two outstanding Advanced Nutrient products—No Shock and Jump Start—to give our pak choi seedlings a head start and a smooth transition.

We place the seedlings in the rockwool cubes into our grow medium, taking extra care that the tender roots are not damaged in any way. Our grow medium consists of polystyrene boards with square holes cut into them to accommodate the rockwool cubes.

These boards are designed to float on the surface of our Nutrient Pond. The plants are given a 42 sq. inch space in which to grow and each square meter of board holds about 37 pak choi plants.

The day temperature in the greenhouse is kept at a steady 25º C (77º F) and the night temperature is allowed to go down to 20º C (68º F). The pH of the pond is automatically adjusted to 5.8, either by using pH Up or pH Down, depending on the circumstances.

The EC of the Pond should measure 1.2 and the dissolved oxygen should be at least 4 mg per Liter. We are going to position air stones at periodic intervals on the bottom of the Pond in order to make sure that the root systems get enough oxygen.

The relative humidity fluctuates between 30 and 70%, depending on the respiratory cycle of the plants, as well as on the continuous CO2 generation. Since the desired ppm of the nutrient solution is 840 ppm which equals the EC reading of 1.2 milliSiemens/cm, we are generating 840 ppm of CO2 to fill up the greenhouse and accelerate growth.

We will be working with the Advanced Nutrients Nutrient Calculator in order to make sure that our basic fertilizer plus root colonizers plus supplements when mixed together do not exceed this level of parts per million.

Our pre-mix tank is where we concoct our nutrient recipe for the optimum health and growth of our pak choi plants. Micro, Grow, B-52, as well as Sensi Cal Mg Grow go into it, as well as Barricade the night before, to ensure a thoroughly dissolved solution.

Barricade is a potassium silicate that is designed to strengthen cell walls and provide great resistance to pests and pathogens. Sensi Cal Grow is necessary to provide for the extra calcium needed to grow healthy leafy vegetables and salad greens.

Chuck relented and agreed to purchase two large size air conditioning units for the two new greenhouses. This way the CO2 will stay where it’s needed the most to help produce extra sugars for the enhanced growth of our pak choi crop.

posted by silvio @ 7:56 PM   0 comments