Bridging the Gap Between Mineral and Organic Plant Nutrition
Plants are autotrophic. In other words, they are able to produce everything they need to grow and reproduce from sunshine, water, carbon dioxide and a handful of essential minerals. Gardeners often debate with each other over the best ways to “feed” their plants, with strong divisions arising between organic and chemical fertilization strategies. The fact is that plants are “self-feeders”, utilizing nutrients from both mineral and organic sources. Plant roots cannot take up large organic molecules. Organic matter must first be broken down by microorganisms in the soil into small ionic molecules that can be easily absorbed by the plant. In essence, organic gardeners are feeding soil-borne microorganisms which in turn feed the plants.
Plants can also be grown in a soil-less environment using pure mineral elements- a process commonly referred to as hydroponic gardening. Mineral elements are mined from the earth, processed into water-soluble form and fed directly to the plant roots as a complete nutrient formula, without the help of microorganisms. In essence, hydroponics may be thought of as creating the perfect soil, providing all of the essential mineral elements in the ideal balance for plant growth. A nitrogen-rich grow formula can be provided at the vegetative growth stage, and a phosphorous and potassium-rich bloom formula can be used at the fruiting and flowering stage. As long as a relatively stress-free environment is maintained, hydroponic systems make it possible to harvest bumper crops of highly nutritious fruits, vegetables and herbs year round. By simply maintaining proper pH and mineral levels, crops can be grown with exceptionally high vitamin content, flavor and yields, without ever touching soil.
Once a baseline of proper fertilization management is established, whether organically or inorganically derived, it is possible to further improve the health and vigor of plants through the judicious use of organic biostimulants. Biostimulants are organic substances that, when applied in small quantities, enhance plant growth and development. Biostimulants improve the uptake of water and nutrients, stimulate the plant’s natural resistance to pests and disease, condition the plants to better handle stress, and generally improve quality and yields. Although biostimulants do not take the place of fertilizers, they help plants utilize fertilizers more efficiently, speeding up the metabolism of the plant while enhancing the plant’s natural immune system.
The secrets of biostimulants are found in nature. In a healthy organic soil, there is a dynamic relationship between the roots of plants and beneficial microorganisms. Enzymes and organic acids from microorganisms break down soil particles and large organic molecules into ionic minerals that plant roots can easily absorb. Microorganisms also provide small organic molecules to the plant, such as growth hormones, amino acids, Krebs cycle intermediates, vitamins and organic chelators. Therefore, most organic biostimulants are derived either from plants, such as seaweed extracts, or from beneficial microorganisms, such as mycorrhizal fungi and plant growth promoting rhizobacteria. The more gardeners know about these additives, the better decisions can be made about their use.
B-Vitamins
There are several vitamins that act as plant biostimulants, but the most popular ones are B1, B2, B3 and B6 because of their positive affect on the metabolism of the plant. Chemical reactions in plant cells are dependant on enzymes, large organic molecules that act as catalysts. Enzymes allow chemical reactions to take place many times faster and more efficiently than under normal conditions. Many enzymes, however, are inactive until turned on by a co-enzyme. B-vitamin derivatives form many of these important co-enzymes.
Seaweed Extracts
The benefits of seaweed extracts have been known to growers for thousands of years, but only in modern times have their active ingredients been identified. Seaweed extracts are rich in natural plant growth hormones and beneficial trace elements, and they are an important component of most biostimulant products found on the market today.
Humic and Fulvic Acids
The greatest value of humic and fulvic acids are their roles as chelators. “Chela” is a Greek word meaning “claw”. Humic and fulvic acids have functional groups that act as claws, holding mineral ions strongly enough to keep them from reacting with other minerals and becoming unavailable to the plant, but weakly enough so that they can be released to the plant cells on demand. Humic acid forms a bridge between clay particles in the soil and potassium ions, making more potassium available to plant roots. Fulvic acid, on the other hand, is a smaller, more biologically-active molecule. Fulvic acid can transport mineral ions directly into the plant and release them where needed the most.
L-Amino Acids
Like humic and fulvic acids, amino are also intermediate chelators, making mineral nutrients more available to the plant. Amino acids have a dramatic affect on calcium uptake by the roots; especially amino acid blends rich in the primary chelators- glutamic acid and glycine. In nature, as in hydroponics, calcium tends to react with phosphates and sulfates, precipitating out of solution as “lime scale”. Amino acid chelators, on the other hand, attach to calcium ions like a claw, preventing them from reacting with other minerals to form lime scale. At the same time, glutamic acid and glycine stimulate root cells to open up calcium ion channels, allowing plants to take up calcium ions thousands to millions of time faster than simple osmosis. Enhanced calcium levels strengthen cell walls, making plants more resistant to pests and fungal diseases, while protecting the plant during times of temperature stress.
Root, Grow and Bloom Stimulants
There is no single biostimulant that cures all ills at every stage of plant development. Instead, the best plant biostimulants are usually a combination of organic and inorganic micronutrients, specifically balanced to steer plant growth in the desired direction. Plant biologists, particularly in the Netherlands and Germany, have spent many years researching plant physiology and developing new organic products that stimulate plant growth, with the added goal of reducing the need for synthetic chemicals and pesticides. Root, grow and bloom stimulants are some of the results of their efforts.
Rooting Hormones
Many gardeners are familiar with rooting powders and gels which are used to root cuttings. Auxins initiate rooting, but once plant roots are actively growing, applying auxins alone would actually restrict root growth! Organic root stimulants do not contain artificial rooting hormones. Instead, they stimulate the plant to produce its own natural rooting hormones to help increase lateral root growth and root mass. In nature, plant growth promoting rhizobacteria produce tryptophan as a byproduct, an amino acid that can easily penetrate cell membranes in the roots. Tryptophan is then transported to the leaves where it is transformed into IAA, the plant’s natural root promoter. Trace elements such as zinc are also necessary in the transformation. So a combination of amino acids, trace elements and organic chelators can have a dramatic effect on active root growth.
Growth Stimulants
Other combinations of plant growth hormones, amino acids and organic acids are better at the vegetative growth stage. Most gardeners know the importance of nitrate and ammonium fertilizers for strong vegetative growth, but inside the root cells, nitrogen is changed into glutamic acid for transport throughout the plant. Applying glutamic acid directly to the roots also aids in the uptake of calcium and potassium, essential elements required for building new cell walls and enhancing carbohydrate metabolism. Seaweed extracts can further enhance the growth process. Seaweed extracts are rich in natural cytokinens, plant growth hormones that stimulate cell division and shoot growth. In addition, beneficial trace elements such as nickel, cobalt and molybdenum facilitate nitrogen metabolism and improve the health and vigor of plants.
Bloom Stimulants
One of the truly revolutionary horticultural innovations of our times is the advent of bloom stimulants. For years, plant scientists have searched for the elusive flowering hormone called “florigen”. Although no one substance has been identified as florigen, biologists have identified a compound directly linked to the flowering process. The compound is called a “zinc finger transcription factor”. It consists of a zinc ion surround by four cysteine molecules, which are amino acids containing sulfur. The sulfur-containing functional groups attach to the DNA molecules in plant cells, turning on the genes that tell the plant to stop making stems and leaves and start making flowering parts. To enhance the process, the internal balance between other plant growth hormones changes, acting as growth suppressors. The energy of the plant goes into the flowers and fruit instead of into vegetative growth.
There is no magic elixir of life. Biochemistry is an intricate dance between thousands of organic and inorganic compounds, working together in a dynamic and exquisitely timed sequence of events. The products of some metabolic processes form the substrates for other chemical reactions, all coordinated by the plant’s genetic code. If plants are to reach their full genetic potential, a bridge must be formed between mineral and organic nutrition. Organic biostimulants promise to bridge that gap; increasing yields, improving resistance to pests and diseases, conditioning plants against environmental stress, and improving the nutritional value of food. If future generations are to feed the world with limited natural resources, we must learn to work with nature, not against it.
BIOSTIMULANT VOCABULARY
Bacillus Subtilis- a common beneficial bacteria that colonizes plant roots.
Beneficial Elements- mineral elements that, though not essential, improve health and vigor of plants.
Biofungicide- organic molecules produced by microorganisms that protect plants against pathogenic fungi.
Biostimulants- organic substances that in small quantities positively affect plant physiology.
Brix- percentage of sugars and other dissolved solids in plant sap or fruit.
B-Vitamins- biostimulants that help stimulate plant metabolism and improve recovery from stress.
Calcium Ion Channels- gated channels in cell membranes that take up calcium thousands to millions of times faster than simple osmosis.
Carbohydrate Metabolism- respiration; the chemical breakdown of sugars into useable energy for plant growth.
Cations- cat-ions; positively charged mineral ions, usually metals.
Chelators- organic acids that attach to cations like a claw, preventing chemical reactions with other elements.
Chirality- left or right-handedness of molecules; left handed molecules are usually more biologically absorbable.
Coenzymes- small organic molecules that turn on enzymes, usually vitamin derivitives.
Electrical Conductivity (EC)- measurement of the concentrated strength of ionic fertilizers.
Enzymatic Hydrolysis- break down of large organic molecules into smaller molecules through the use of enzymes.
Enzymes- protein molecules that catalyze chemical reactions; one gene = one enzyme.
Essential Element- one of 17 mineral elements without which plants could not live and reproduce.
Humic and Fulvic Acids- organic acids extracted from prehistoric compost piles.
Hydroponics- a method of growing plants without soil using mineral fertilizers and water.
Hyphae- the threadlike filaments formed by fungi.
Ionic Minerals- inorganic minerals that conduct an electrical charge in water.
Krebs Cycle Intermediates- organic acids that are the byproducts of the steps of cellular metabolism.
L-Amino Acids- organic acids derived from the enzymatic hydrolysis of proteins.
Metallic Co-factors- metal ions, such as copper, zinc, iron and manganese, that turn on enzymes.
Mitochondria- the power plants of the cell; organelles in which carbohydrate metabolism takes place.
Mycorrhizal Fungi- root fungus; beneficial fungi that form symbiotic relationships with plant roots.
Organic Molecules- carbon-containing molecules that form living tissue.
Pectin- the calcium and magnesium salts of pectic acid that forms the “glue” that holds plant cell walls together.
Photosynthesis- the chemical process in green plants that uses light energy to transform carbon dioxide and water into simple sugars.
Phytoalexins- natural chemicals produced by plants to fend off pests and diseases.
Plant Growth Hormones- small organic molecules that trigger physiological changes in the plant.
Plant Growth Promoting Rhizobacteria (PGPR)- bacteria that colonize plant roots and produce substances beneficial to plants.
Protease- an enzyme that breaks down proteins into amino acids.
Respiration- the opposite of photosynthesis; the process by which sugars are broken down into water and carbon dioxide, releasing energy for plant growth.
Root, Grow and Bloom Stimulants- specific combinations of biostimulants that direct the energy of the plant into desired forms of growth.
Seaweed Extracts- concentrated liquid biostimulant processed from the brown seaweed ascophylum nodosum.
Secondary Metabolites- natural chemicals produced by plants in response to pathogens or environmental stress.
Siderophores- proteins produced by microorganisms that sequester iron.
Superoxide Dismutase (SOD)- enzyme that breaks down superoxide, protecting cellular membranes.
Synergistic- when two or more substances work much better together than either one alone.
Systemic Acquired Resistance (SAR)- plant response to a single attack in which the plant becomes resistant to future attacks for an extended period of time.
Tryptophan- amino acid that is transformed into auxins by the plant and pumped to growing tips.
Zinc Finger Transcription Factor- one zinc ion surrounded by four molecules of the amino acid cysteine; it attaches to DNA and turns on the genes that promote flowering.
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