Monday, February 21, 2011

Questions and Answers - Hydroponics Panel at ProGreen EXPO 2011

ProGreen EXPO 2011 in Denver earlier this month was a great success. This annual event is the single best regional green industry show in the Rocky Mountain West. There were over 140 seminars on both the most basic and the hottest topics in the green industry, plus over 650 exhibit booths of interesting products and services.

On the final day at ProGreen, I hosted an open panel on hydroponic greenhouse production with three nationally recognized experts in hydroponics. We spent an hour responding to questions from the audience. The dialogue is summarized below.

Who were the panelists?

Questions from the audience with answers from the panelists:

Recently, the Oregon Department of Agriculture released a stop sales order on many fertilizers that are not legal for sale or distribution in the state of Oregon due to failure to register. What is the opinion of the panel on this issue?
First, the State of Oregon is trying to protect the consumer from fraudulent products and fraudulent claims that often result from untested or unregistered fertilizer products. Next, their intention is to protect the environment from inappropriate use of fertilizers resulting in excess runoff into the waterways.
The rule making organizations that are creating and enforcing the rules do not always have all of the knowledge that they need to make appropriate decisions. Therefore, they rely on the registration procedures that they have developed and are trying to support those companies who manufacture products based on good science. The majority of the products on the stop sales list are either not registered with the state of Oregon or are mislabeled.
What is the suggested filtration process for disposing hydroponic wastes?
Hydroponic solutions that are no longer useful for maintaining plant growth is high in fertilizers, dissolved solids, and potentially plant pathogens. It is not appropriate to dispose of these solutions as storm water or sanitary sewage.
The ideal disposal process is through bioremediation through application on secondary and tertiary crops. Ideally these should be plants you can sell, such as nursery crops or turfgrass sod. The waste solution needs to be drained, collected, and stored in a safe and efficient way. From there it can be pumped outdoors to a turfgrass site or other outdoor crops.
Treatment of the effluent using reverse osmosis is expensive. The use of constructed wetlands is an additional alternative worth exploring.
Can the wood from Mountain Pine Bark Beetle killed trees be used as a hydroponic substrate?
Pine bark is a very effective growing medium for hydroponic production and has been used by many growers successfully. There has been a great deal of research conducted comparing sphagnum peat moss, coconut fiber, etc. (see the Mississippi State University Greenhouse Tomato Handbook).
Pine wood waste is high in cellulose and requires composting to make good soil substrate. Pine bark is high in lignin and resistant to degradation. 
The biggest issue with the use of beetle-killed trees is access. Most of the trees are in hard to reach areas and the expense of harvest, shipping, and processing makes this product cost prohibitive.
Many of the tomato cultivars that we are growing taste terrible. Are the varieties getting better and what is the future of tomato selections?
Flavor of tomatoes grown in the greenhouse is based on solar load, the pH of the hydroponic solution, and the nutrient status of the plants. Greenhouse production in the spring (Mississippi) provides more sun than the fall, which yields better tasting fruit. Most people like an acid flavor with the sweetness. The pH of the solution does have an impact.
What about varieties? Seed suppliers base their product lines somewhat based on what customers want. Older varieties (heritage included) lack modern disease resistance. Yet, many customers think that older varieties have better flavor.
De Ruiter Seeds, one of the largest greenhouse vegetable seed suppliers, is now owned by Monsanto. Their corporate approach is to determine the best seed sales and eliminate those varieties that do not meet market demands. Therefore, they are eliminating some varieties that are not selling well on an international scale. Ultimately, this is resulting in the loss of some good varieties, such as Blitz.
Summer tomatoes tend to taste better in summer due to stress due to heat and water stress. Pushing yields to compete with field growers is probably costing us some flavor.
Grafting heirlooms onto modern cultivars with more disease resistance will improve yield and flavor.
What is the projected yield on grafted heirloom tomato cultivars?
The first fruit cluster will yield well and then dwindle on future clusters. Genetically, most heirlooms will behave determinately and not bear fruit over the long term.
Do we have tomato cultivars that have higher nutritional content?
The longer tomato fruit are kept on the vine, the higher the nutritional value and flavor. Fruit harvested green or as breakers will not yield the best flavor. This is the same for hydroponic and field production.
Are there programs breeding tomatoes for higher nutrition?
Most tomato breeders are working on increased yield and disease resistance.
What is the difference between natural sunshine and artificial light? Does artificial lighting grow plants just as good as natural sunlight?
The answer is yes and no. High pressure sodium lamps do grow good plants, but it does not provide adequate heat stress on the plant resulting in some loss of flavor. There is a considerable amount of effort on LED lamps. Those on the panel did not have any specific experience, but are paying attention to the literature.
For the best wavelengths to grow plants, use light sources that provide PAR (photosynthetic active radiation) lighting. Remember that light intensity drops significantly as distance from the lamp increases. Northern European growers use high pressure sodium to extend photoperiod primarily, but their electric power is cheaper than what we have in North America. In Colorado, with few cloudy days, supplemental light is probably unnecessary. It is difficult to acquire the appropriate solar load, which leads to high costs for tomatoes. Other crops with higher value may benefit from lighting.
What is the appropriate spectrum for growing tomatoes under artificial light?
High pressure sodium lamps have poorly balanced red and blue spectra, but plants seem to grow well. There is a great deal of LED research for supplemental light in the proper blue-red balance is underway at many research centers.
Blue light, such as that from metal halide lamps, has shown plants to become more susceptible to insect infestations. Blending light from high pressure sodium with T-5 fluorescents will add some blue for a better balance when using high pressure sodium.
When using coconut fiber (coir), should it be charges with fertilizer for earlier cluster yields?
Coir is the dust and fibers from the mesocarp of a coconut fruit. It can be a great resource for growers as a root substrate because it is available in large quantities and is an agricultural waste product. However, coconut palm trees are resistant to high levels of sodium and grow in coastal areas. Therefore, some coconut fibers are high in sodium. Some processors do not rinse their product well prior to compression. Fresh coconut fiber should be soaked in a solution in calcium nitrate overnight will push out the sodium (total use a calcium nitrate solution with an electrical conductivity of 3 or 4 dS/m). 
What plastics are best used for the floor of a tomato greenhouse?
White plastic is reflective increasing light distribution, but the plastic used needs a uv inhibitor blended during its manufacture. Black plastic does not degrade as quickly as white, but it does not provide reflection. There are plastic products available that are co-extruded with white and plastic layers, but they are expensive. Consider using food-grade polyethylene for your plants. Polypropylene is also an option. Remember, black plastics can be painted white.
What is the best way to recycle rockwool used as a root substrate?
Rockwool is widely used in Europe and they have mandatory recycling programs often incorporating it into asphalt. Some growers have tried to recycle rockwool into potting media for bedding plants, but the issue of removing the plastic and the plant debris makes this practice cost prohibitive.

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