Plant nutrition research update

by Steve Wagner
Stephanie Brace is a horticulture Ph.D candidate at Cornell University, and her topic for a Gro Research webinar was Vermicompost Usage as an Organic Fertilizer. Compost feedstock is made up of food scraps, animal waste and bedding (pig, horse, and cow manures), sawdust (occasionally), and elements from the bait industry. The other part of the equation is the worms that are used, which are primarily eisinia fetida (red wigglers). Factors that make vermicompost organic are allowed feedstock (the aforementioned feed scraps, etc.); and composting (thermophilic) which must be heated to between 130 and 170, or three days in an aerated system. “You do not want the heat to rise very high,” says Brace, “or else you’ll kill the worms. But the material is kept aerated at 70-to-90-percent moisture. When using manure-based products,” she says, “you have to be a little more careful to not use the wrong manure on your plants. The main thing is to keep records and check with your certifying agencies.”
Brace then compared two of the vermicompost trials they conducted. In the first one, they compared four sources and used them to grow tomatoes and peppers to compare the plant growth. Nitrates demonstrated relatively high levels across the board, manure-based ones being the highest. We found noticeable plant differences in growing tomatoes. Looking at peppers, using the same substrates, at a certain point past the 10 percent application rate, there was a decrease in growth.
If there is a “take home” message here, or strategies for success, they are relatively simple. There is no one size fits all fertilizer regime. Not all vermicomposts are equal. Fertility levels differ based on feedstock. Some vermicomposts are more suitable as substrate amendment than as organic fertilizer sources. Conduct your own house trials with new materials. Monitor supplies or batches for consistency. And ask for analysis of materials.
Silicon Fertilizer Enhances Stress Tolerance of Bedding and Potted Plants
The final presentation of this Cornell webinar featured research on silicon.
Si, as it’s known to many, is the 14^th element on the Periodic Table. And it is the second largest soil constituent. Any information beyond that gets us into Chemistry 101. It’s Neil Mattson, Cornell Plant Nutrition Research Specialist to the rescue. “Plants are growing in an environment where there is a lot of silicon around,” he explained. “And with this, plants take up orthosilicic acid. That is silicon connected to four oxygens connected to four hydrogens. Once plants take up silicon there is deposition in their shoot tissues.” For example, “rice is about five percent silicon by dry weight, and scientists have found the actual genetics related to silicon uptake in the root.” Ergo, rice roots are actively selecting for and absorbing silicon and transporting it to the shoots. Mattson says that a question arose about five years ago, ‘Do floriculture species in a soilless substrate take up silicon?’ “To answer that question, we screened 21 different floriculture species to determine if supplemental silicon enhances leaf tissue silicon. We were giving the plants weekly drenches with 112 ppm potassium silicate. We did that for 10 weeks.”
Conclusions from the initial screening were that weekly silicon supplementation did increase leaf silicon for half of the species that were studied. Differential silicon accumulation was not required to see a growth effect. Mattson said, “In subsequent work, we decided to grow plants with and without silicon, and impose stresses, to see if there were benefits on the plant.” Experiments involving salt were the first stress tests utilizing 28 species of plants. Seedlings were transplanted into a soilless substrate, fertilized daily, treated for five weeks, and harvested. Weekly Si supplementation increased leaf Si concentration for half of the species studied. And it should be noted that in the absence of (a)biotic stresses, Si did not have any dramatic effects on plant growth.
“Another experiment we did was done by Roland Leatherwood,” a specialist in post-harvest physiology, “and we grew poinsettias in a greenhouse with silicon. This was another case where we gave silicon at about 50ppm as part of the standard fertilizer regime. Once poinsettias reached commercial marketability we took the plants out of the greenhouse and brought them to a room.” They were kept at room temperature with fluorescent lights for 12 hours a day to emulate keeping the plant in an indoor environment. “The plants were well watered before we took them to that room,” Mattson said, “and then we stopped watering, and came back to them to see how many days it took them to wilt. Our silicon treated plants lasted about three or four days more before wilting.” Citing a Peterstar Red variety, he pointed out that was 12 days postharvest that did not have silicon and was already quite wilted, and compared it to a silicon-treated poinsettia “that was still turgid, and looking marketable.” His point is that silicon can be used to increase poinsettia shelf life if they’re not going to be watered in a retail setting such as big box stores. “We waited until the plants were wilted and we re-watered them. Silicon-treated plants showed recovery from wilt as well.”
The final silicon experiment was with heat stress. Petunias growing in a greenhouse for several weeks had a once-a-week drench of 100 ppm silicon for several weeks; others in a control group did not. In a special chamber, temperatures were ratcheted up to 95 degrees and 102 degrees Fahrenheit (heat stress), “which we kept going for 24 hours,” said Mattson. Studying photos of the results at 102 degrees, he said “all the plants are looking pretty bad, but the silicon-treated plants are more upright and showing less wilting. It is even more obvious at the 95 degree temperature. Three days after that 102 degree treatment the plants were actually starting to acclimate to that heat stress, starting to get used to it. They don’t look as bad as they did just after one day.”
A couple of caveats from Mattson before we depart: Tap water, fertilizer or substrate does not continually supply silicon as a contaminant. And silicon is not a miracle cure for every stress.