"It's not what you eat, it's what you absorb," a phrase that applies equally to the uptake of essential nutrients by plants. Application of an essential plant nutrient does not always mean that the plant will be able to uptake that mineral and then move it through the vascular system into the plant tissues.
The availability of plant nutrients is in fact dictated by the form of the mineral, environmental temperature, humidity, photosynthesis, pH of the root zone, and most importantly the relative concentration of each mineral in the nutrient solution. It is the balance of these minerals that are often forgotten when growers are formulating plant nutrient recipes and adding supplements to reach specifically targeted mineral compositions.
There is a well-known system that classifies essential plant nutrients into "macro" and "micro" categories based on their concentrations in the plant tissue. Less understood is the relationship of the electrical charge of the individual ions and how it affects their bioavailability to the plant. Ions exist as either positively charged (cations) or negatively charged (anions) depending on the balance of electrons (negative) versus protons (positive). It is the strength of the ionic charge that will affect the movement of the ions into and out of the plant. By understanding the strength of the positive or negative charge of essential plant nutrients, we can begin to comprehend the selective ion uptake mechanisms of a plant's physiology. The table below shows the elemental forms of plant nutrients and their ionic charges in the forms that are available for plant uptake.
The movement of ions into plant roots occurs by both active and passive transport. Passive transport means that the ions are carried with the uptake of water into the plant without energy from the plant. The water movement factors that affect passive transport are temperature, humidity, photosynthesis rates, the concentration of ions in solution versus within the plant cell, and plant transpiration rates based on the stage of growth. Active transport requires energy from the plant and ion movement is determined by competition between ions based on their individual charge. The monovalent ions (single charged) are moved into the plant more easily than divalent ions (double charged), while divalent ions are taken up more easily than trivalent ions (triple charged). This means that the plant will accumulate more potassium (a monovalent ion) than calcium and magnesium (divalent ions) due to the difference in their charge. Plants typically maintain a negative interior (inside the plasma membrane) relative to the exterior. The slightly negative state of the cell interior and the environment must be maintained and, thus, is related to ion uptake. When there are more cations than anions present, the overall charge becomes excessively positive, and an increase in anions or a decrease in cation uptake occurs to restore physiological conditions. For example, an excess of ammonium (NH4+) cations decreases the uptake of potassium (K+), calcium (Ca2+), and Magnesium (Mg2+). The same relationship exists for anions - excess anions lead to a lower uptake of anions or an increase in cations to balance the cell’s charge. If nitrate (NO3-) is the major anion in excess, then the uptake of cations such as potassium (K+), calcium (Ca2+), and Magnesium (Mg2+) will increase to compensate for the overall negative charge caused by excess nitrate levels.
Many growers give themselves labels based on the types of inputs they use in their gardens, often referring to "strict organic practices" or "sterile, mineral-based hydro". Perhaps you're the type of gardener who avoids "chemicals", or only uses "organics", but can you define these terms? What makes something truly organic? Every grower should understand what they put into their gardens and why.
What is a chemical?
When we use words like chemicals or chemistry, we are simply referring to the study and use of elements from the Periodic Table. The elements found in the Periodic Table are the basic atoms that make up everything on this planet and many chemicals that exist in the natural world. All Plants produce chemicals throughout their life cycle. In an organic garden, we rely on microorganisms to convert organic matter into chemical forms that are taken up by plants. Chemicals can originate from natural sources. In some respects, organic gardening is a natural way of feeding chemicals to plants.
So, the next logical question: What is Organic?
Chemists and physicists will tell you that nearly any compound containing carbon is organic, whether that compound is natural or not. The truth is many natural substances are not organic. For example, certain types of naturally occurring rocks are crushed to make fertilizers that contain inorganic phosphorus. Those rocks are technically inorganic, even though they were mined directly from the ground. Many gardeners and agricultural professionals use the word organic to describe fertilizers and plant products that are derived exclusively from plants and animals (manure, kelp, bone meal, etc.). By that definition of the word, Organic growers cannot use inorganic substances, even if they occur naturally.
One thing to keep in mind: many organic garden products contain inorganic salts. Two popular examples are bat guano and seaweed extract. Because these are derived from animals and plants, they qualify for organic gardening. However, the lab analysis shows a dash of inorganic material included in the final products.
Confused yet?
What are Minerals?
The Periodic Table contains (among other things) the 17 elements required for plants to live: carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, boron, chlorine, copper, iron, manganese, molybdenum, nickel, and zinc. Many scientists and university studies give evidence that silicon should be added to that list as well. Minerals occur in nature, but they are not sourced from plants or animals. These minerals may come from crushed rocks, or they may be generated in a lab via chemical processes. When looking at basic elements and minerals, there is no difference between the crushed rock form and the laboratory derivative. It may take millions of years to accumulate rock formations, which then have to be mined and pulverized, so the laboratory version is much faster. Mining can be quite harmful to the environment, not to mention, expensive and unsafe for workers. Depending on the specific element, one method may be better suited than another for obtaining these minerals with the least environmental and budgetary impact.
In recent years, there has been increased discussion regarding the use of high-quality or low-quality minerals in plant foods. The real difference in quality can be determined by the level of contaminants in the final product. Pure, uncontaminated elements are the same, regardless of the source. Elements and compounds that are not available to plants can bog down roots and slow nutrient absorption and availability. For the highest quality mineral plant foods, avoid contaminants and questionable ingredients.
Reasons for using organics
There is little argument that mineral fertilizers can more easily burn plants if used carelessly. Overfeeding is always a concern, but is less likely when using organics. Microbes and fungi must work to convert elements into plant available forms, which slows reactions in the root zone as it becomes nutrient rich. While overfeeding with organics is possible, the microbiology at work in the root zone offers a natural buffer. The flavour of organically grown tomatoes, culinary herbs, and resin-producing plants is often said to be better and more complex than crops grown with minerals. The fact is that low-quality or high-quality harvests can be grown with either mineral or organic inputs. One reason why well maintained organic gardens often produce very deep aromas and flavours is, in part, because overfeeding has been avoided.
Reasons for Using Minerals
We live in an age where plant chemistry and biology have been analyzed to an exacting degree. Scientists have discovered which elements are taken up by plants, and the specific ratios required for optimum performance. Mineral nutrient formulations can be made using highly available forms, allowing plants to absorb them right away. This process can lead to faster growth, bigger harvests, and increased quality. Many hobby gardeners grow delicious tomatoes in their backyards, using mineral salts from the local garden centre. Even without organics, mineral-grown crops can offer increased flavours and aromas, as long as the grower does not over-use plant foods or harvest prematurely. Attention to detail is required when using mineral fertilizers, and there is no need to sacrifice quality by overdosing plants. When given the correct amounts of mineral inputs, plants can achieve optimum health. Overall plant health is the key to both higher yield and quality.
Hybrid Nutrient Systems
Growers all over the world have achieved big yields and potent flavours by using organics and minerals together. Both offer unique benefits, and there is no reason you can't use them in tandem to get the best of both worlds.
Many naturally occurring inorganic compounds are not only safe for plants, they are safe enough for you to eat! Don't reject the idea of using organics, minerals or both before doing some research on the pros, cons and effectiveness of each type of nutrient.
What are you feeding your plants?
Not every garden product should be assumed to be safe or effective. Learn about the elements your plants require and the additional organic inputs that offer increased quality. With a little bit of knowledge and high-quality plant nutrients whether organic, mineral, or both, your garden will flourish!