All living things need a source of carbon generally known as food. Animals eat their food, fungi absorb theirs, and plants make their own via photosynthesis. Plants must also obtain other necessary raw materials directly from the environment. These raw materials are mineral elements in ionic form. Light and air do a lot for a plant but they can’t do it all. Which is why fertilization, the providing of mineral elements essential for healthy plant growth and development, is an important part of any plant production system.
Fertilizers are produced with a wide range of compositions to make them applicable to virtually any situation (plant species, environmental conditions, phase of growth, etc.) but they come in only one of two basic forms—liquid or solid. Each has its advantages and disadvantages.
An examination of the nutrient shelves at a typical supplier reveals that the majority of fertilizers for hydroponic use are provided in liquid form. There are some good reasons for this. Concentrated liquid nutrients are easily diluted, and pouring, mixing, and transferring are straightforward operations. And, since hydroponics is a liquid process to begin with, it just seems natural for the inputs to be in liquid form as well. Not only that, but there are manufacturing considerations that have led many producers of hydroponic nutrients to go the liquid route.
Let’s not ignore the possibilities of nutrients provided in solid dry form, though. What are the key points to consider when choosing between dry and liquid fertilizers for hydroponics?
Highly soluble dry powdered compounds are much more concentrated than their liquid counterparts thus weighing less and taking up less space for the same quantity of elements. Liquid nutrients contain a significant amount of water, and water is heavy. Users of large amounts of nutrients often buy in bulk for the best price and bulk solids are not only lighter, but easier to transport, and easier to store compared to liquid formulations. The difference might not mean much to a casual grower, but for anyone handling large quantities, dry fertilizers can save transportation costs and space.
Another advantage of dry fertilizers is in their actual use. At first, it may be a bit less convenient to measure (usually by mass or weight) powdered material to create nutrient solutions, but once the procedures are standardized, it takes about the same amount of time, perhaps even less, as it does to prepare solutions starting with liquids. Most people find it is easier to accurately weigh a small amount of material on a good balance than it is to get an accurate liquid volume using a graduated cylinder (if you are not accurately measuring your liquid volumes, your results are only approximate anyway). Once standardized preparation procedures are in place, containers sized to hold exact desired masses can be used, bypassing the need for weighing altogether, and reducing the chance of error. If employees need training, it is just as easy to train them in preparing solutions from solids as it is from liquids.
Unlike liquid fertilizers, solid fertilizers can be made with variable properties based on solubility and particle size. Solubility can be controlled by selection of specific binding agents to hold the nutrient particle matrix together. Organic or inorganic coatings can also be applied to solid particles to control the rate of dissolution of the encapsulated nutrient material. Particle size also affects solubility. The particle size of solid fertilizers ranges from fine and powdery for typical high solubility formulations to large and granular for application to solid substrates. Granular products are well suited for inclusion in or topdressing of soil, sand, or coir, and under some conditions for use with gravel, rock, or expanded clay. The customizable solubility and particle size of dry fertilizers allows for the creation of controlled release formulations. Particles that dissolve slowly are able to provide plants with the elements they need for extended periods without overloading the root zone with salts.
In any case, once a mineral element is made available for plant uptake, no one can tell if it was made by mixing liquids or by dissolving solids. A solution is a solution no matter how it is made. Plants certainly can’t tell the difference.