The Wonder of Plants
The practice of plant husbandry began with early man. Even before we had the slightest concept of plant physiology, it was observed that certain conditions had an influence on plant health and vigor. Eventually we began to select and organize desirable plant types and contribute to their basic requirements. We suspected that there was something in the soil that plants consumed but it took thousands of years to stumble upon even the most basic understanding of the science of plant chemistry. Only in the last one hundred years has technology advanced to the point that we can accurately measure and manipulate a plants internal functions. And even more recently isolate and identify plant substances genetically and at an atomic level. This knowledge has allowed us to breed and propagate specialized flower, food, and resource crops, more prolific and abundant then ever before. We must use good judgement because our ability to alter the natural way of things is a power not to be used haphazardly.
Our goal is to provide select and precise constituents to a plant growth environment, in a properly balanced manner, neither lacking or in excess. Most people realize that living plants are a complex organism, whose internal functions are generally taken for granted. Some people seem to have a sense of awareness and unity with plants, while others simply see an inanimate object.
What do you see? Do you see water and minerals moving across and into the roots, and traveling through stem and branches into living leaf cells? Or the water molecules evaporate out through the open leaf stomates? Do you see the CO2 molecules diffusing into the chloroplasts, and then being fixed by photosynthesis into carbohydrates which then travel by vascular pathways to all points of demand? Do you see the ions from essential minerals being selectively absorbed and combined into coenzymes and organic compounds? Do you see the nourished cells split and reproduce to form the splendor of foliage and flower we see before us? Of course not, but it is happening, and we can gain at least a sense of awareness that it is.
A plant, as any living organism, is a marvel of chemistry, yet it operates much like a machine, governed by the laws of physics. This being the case it stands to reason that anyone can learn to grow plants. Especially with the technology and automated systems available today. Maybe it's not necessary to understand the internal workings of a plant to successfully manage a growing operation and produce plentiful crops.
The properties of air and water and the substances dissolved in them begins the miracle of plant physiology. There is what seems a dimensionless symphony of chemistry occurring at a molecular level all around us. Plant systems are dependent upon these basic constituents: light/heat, CO2 water, and essential minerals. As growers, our task is to provide all of these requirements in a plentiful and properly balanced fashion. This booklet will deal primarily with functions related to nutrient assimilation and the management practices necessary to maintain ample solution properties. We will address the concern of fluid as a means of translocating nutrient elements into the plant and its cell structures. We will touch on some of the fundamentals of plant physiology and attempt to address some of the most frequently misunderstood aspects of plant science.
Plants consist of a complex arrangement of cell bodies working together, each in their own way to form a living organism. These cells are made up of, or contain many components such as proteins, polysaccharides, amino and organic acids, lignin's etc. These compounds are themselves comprised of principle elements which over 80% (as dry weight) consist of oxygen and carbon. Followed respectively in quantitative sequence is hydrogen, nitrogen, silicon, potassium, calcium, sulfur, phosphorus, magnesium, aluminum, iron, chlorine, sodium, manganese, boron, copper, zinc, molybdenum and other assorted scarce minerals. Different combinations of these constituents form molecules of many identities to construct new cells and tissues. This is why these essential elements must be readily available. These sixteen elements, along with water and sunlight, plants are able to synthesize all the compounds they require, as well as, vitamins and enzymes necessary to us as consumers. These essential elements can be provided in their elemental form, pure and immediately available, with the application of high quality inorganic fertilizers. These essential elements can also be found in organic molecules (such as found in soils) however, organic materials must be broken down into their pure elemental (inorganic) form before they can be utilized by the plant. Additional energy is required to disassociate these more complex organic commodities. Plants will absorb and accumulate numerous nonessential elements. Plants can uptake, breakdown, or retain many substances. If these substances are beneficial it could be desirable but if they are toxic it could be disastrous. Many elements have been found in plant tissue which are not known to have any influence on plant metabolism. Lead, arsenic, mercury, gold and fluoride are among the more than 60 other known elements.
Roots not only provide a means of support, but they act as receptors providing pathways for select solutions and substances to be regulated into the plants circulatory systems. Root anatomy consists primarily of a xylem and phloem core of vascular tissue, surrounded by a cortex tissue and an outer layer of epidermal tissue. Microscopic projections called root hairs usually develop on the epidermal cell to further enhance the water absorption capability of the root surface. These follicles are very delicate and should be protected from dryness, extreme temperatures, harsh chemicals or abrasion. Root health is vital, as the survival of the whole plant depends on it.
Roots are specially adapted tissues which readily absorb aqueous substances and transport them into the plants main vascular system. This vascular network originates at the tips of the roots and is continuous throughout the plant. Absorption is supported by the process of diffusion. Diffusion is the process by which ions and molecules distribute uniformly throughout a contiguous volume. Nutrient ions will diffuse into the root, between it's cells, through intercellular spaces called the apoplast, and interconnecting protoplasm called the symplast. These pathways allow water and solutes to pass across the cortex and through the endodermal layer and into the vascular bundles. Xylem and phloem bundles guide solutions through the plants roots and stem. The xylem tissue forms the vessels that channel solutions up into the plant and the phloem tissues primarily distribute internally manufactured foods throughout the plant. Once in the main phloem it is transferred to all parts of the plant. All plant cells, each with a different appetite, will be exposed to these fluids and accumulate the nutrients they require to achieve their assigned functions.
The movement of solution through the plant is a complex combination of internal and external forces. This force is then used by the plant in a variety of ways, some of which include:
1. To deliver essential substances to the various internal mechanisms as well as removing waste products.
2. To provide systemic pressure to give the plant structural integrity.
3. To facilitate cooling of plant tissues by transfer and evaporation.
Solutions travel throughout the plants leaves and stems via capillary channels called veins. These vascular bundles perform two modes of transport. First to deliver water and nutrients to all cellular tissues for assimilation and second to translocate manufactured food substances (photosynthates) from the point of photosynthesis to all parts of the plant (flowers, fruit, meristems, etc.). These conduits are called the xylem and the phloem tissues.
Many factors play a role in moving solutions through the plant's circulatory system: absorption, capillary action, cohesion, menisci, hydration and root pressure, to mention a few. The combination of these forces serves to propel solution up and throughout the plant. Transpiration is the major contributor to this process. Simply put, it is the affinity of dry air to obtain water vapor. As the air removes water from the leaf, it literally draws more up into the plant to replace it. This captivation relies upon the cohesion of water molecules (a term for the attraction of one water molecule for another) which literally pulls water up the plants vascular capillaries like a chain. These fluids are the life blood of the plant and must be available consistently for good health. The use of a high quality plant nutrient will assure that the transport system will function properly.
Within a plant's structure exist many types of cells. These cells vary in their ability to absorb solutes by the nature of their membranes. A solute could be anything dissolved in a solvent (water). Membranes are thin permeable tissues which surround the cell bodies. These cell membranes are designed to be specific to which elements are able to pass through them. The following forces control this flow (flux) process.
1. Osmosis is the tendency for a solvent (in our case water) to pass through a membrane from the side of less soluble salts to the side of higher concentration. It is attempting to dilute the solution to gain equilibrium on each side. This action is regulated by particle concentration, not by their properties. When this activity is measured it is termed the chemical potential.
2. The second type of membrane flow is called the electrical potential. This force is driven by the exchange of positive (cation) and negative (anions) ions creating a + or - potential within the cell. A positive affinity will generally attract negative ions to balance its polarity (and vise versa). This creates a flow of ions by electrical attraction.
3. Another method involves the use of a carrier molecule, often part of the membrane itself. If an ion is attracted to a site on a carrier molecule, it may then diffuse readily across the membrane to be released on the other side. This method controls ion selectivity by the ability of the carrier to combine with a specific element ion. This explains why only certain ions are able to pass through a given membrane tissue type.
Many factors and conditions effect these processes and their ability to absorb essential elements. Among these are, nutrient solution concentration, balance, pH, temperature, or the presence of incompatible chemicals which may bind and inhibit important minerals from being available to the plants.
The scientific definition of organic is "any chemical compound containing carbon". A more common interpretation is any substance derived from living organisms, plant or animal. The concept of organic gardening usually implies that, the essential elements required for plant nutrition will be attained by dissociation from decomposing matter. This process occurs in nature when a plant or animal expires or sheds tissue which is then systematically acted upon by organisms and environmental conditions. These influences range from abrasion, dissolution, combustion, chemical reduction, to consumption by man or animals. When organic matter is consumed and digested by microorganisms (primarily bacterium), it is broken down and released as enzymes of proteins, starches, vitamins, hormones and other such metabolites. Some of these compounds can be taken up into the plant and stored, or selectively utilized by the plant for metabolic functions. These processes of plant chemistry are very complex electrochemical interactions which take place in a series of stages, in an infinite chain of events not yet fully defined by science. The end result of all of this is to provide pure inorganic elements which are the building blocks of all life.
The term "inorganic" defines a substance as a non-living material neither of plant or animal origin. Generally referring to matter not containing carbon. All organic structures are composed of inorganic compounds and will eventually degrade back to this original form. Pure inorganic elements and combinations thereof, are the foundation of all living things (and otherwise) on this planet. The mysterious interactions of these 103 elements somehow manages to create or at least sustain life and all things of substance.
When used in a horticultural context, it describes the type of feeding program which utilizes basic elemental complexes as mineral salts. About fifteen (15) of these elements are known to be essential for normal plant growth. When these elements are in solution they become available (to some degree) for plants to assimilate, either in their pure form or as ions of simple compounds. All essential substances necessary for plant functions can be manufactured by the plant from these inorganic elements. When these elements are combined into compatible compounds, they are referred to as chemical fertilizers. These carefully balanced nutrient blends allow us to provide, pure and precise allocations of mineral elements and encourage the type of plant response desired. Hydroponic techniques have proven that pure elemental solutions are the most dependable and predictable way to insure optimum productivity. These methods allow us to totally isolate and contain a complete grow system. Solutions may be circulated and recovered and re-proportioned for subsequent use. This can mean tremendous benefits in terms of ecology, productivity, economy, and application. These methods can provide food for people in areas where conventional farming methods would not be possible.
Chemical fertilizers have undeservingly been given a bad rap because they have been associated with large scale wasteful misuse. This has resulted in the contamination of soils and water supplies. This is not the fault of the chemical, rather the management thereof. Another unfair association is that of pesticides, fungicides, herbicides, inoculates, and preservatives etc., of which chemical fertilizers have no relationship. Chemicals compounds are not undesirable just because it has been refined or combined by man.
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