ABSTRACT
Many people are of the opinion that hydroponics is all chemistry and that the plants grown by this technique are “inorganic” (Figure 4�1), which is not true� Some basic high-school level chemistry will help one understand how to prepare nutrient formulations, but even without such a background one can easily learn the procedures� Preparing nutrient solutions can also be done by purchasing ready-made nutrient mixtures� As far as the plants are concerned, they require the same essential elements regardless of whether they are obtained from hydroponic sources or by natural breakdown in the soil� The advantage of hydroponics is that one can provide the plants with optimum levels of each of the essential elements through the nutrient solution formulation (Figure 4�2)� When growing in soil these same nutrients are added by the application of fertilizers and compost� However, because of the heterogeneity of the soil, it is more difficult to apply the nutrients at levels that are optimum for plant growth (Figure 4�3)�
The nature and properties of the soil determine the availability of nutrients to plants� Different types of soils, such as, sand, sandy loam, loam and clay, are determined by their percentages of natural inorganic particle sizes and organic matter� Sandy soil composed of large mineral particles permits water and nutrients to move quickly through it and past the root zone of plants� These are not ideal for vegetable growing unless large amounts of water and fertilizers are supplied regularly� Pure igneous (volcanic) sand in fact is suitable as a hydroponic medium, where oxygenation to plant roots is readily available� At the other extreme is clayey soil that consists mainly of small particles that hold together tightly retaining water and minerals� This type of soil often has excess water with poor drainage causing lack of oxygen to plant roots� With this poor aeration, plants also suffer from lack of mineral uptake� A loamy soil has a good mixture of large and small minerals plus organic matter (humus), which provides adequate minerals, water, and oxygen to the plants� Maintaining soils in this optimum state of structure and fertility is often challenging, requiring soil tests and frequent additions of fertilizers and compost of adequate quantities for plant growth�
With hydroponics, the choice of substrate depends on the availability, cost, crop, water retention, oxygenation, structural integrity, and sterility� For most backyard gardeners, the availability and cost of the substrate are not restrictive because they use relatively small amounts� Some crops grow better in more porous substrates, whereas others grow well where there is higher water retention� However, oxygenation is important to all plants, so drainage is critical, especially for long-term crops such as tomatoes, peppers, eggplants, cucumbers, and other vine crops� Some shortterm crops, such as herbs (basil, mint, and watercress) and lettuce can grow in water
culture systems� Structural integrity, the ability of the substrate to retain its structure and not break down during the growth of the plants, is basic to hydroponic growing� This quality and sterility are of prime importance in the selection of a medium� If the substrate is not free of pest and disease organisms, they will attack the plant roots causing decreased plant vigor and yields� You will then be in a similar situation as what often occurs with soil growing� All of the variable properties of soils that can restrict plant growth through lack of oxygen and mineral availability, and/or occurrence of structural breakdown, and the presence of pests and diseases are difficult to
control� With hydroponics, you choose the best substrate that provides optimum levels of oxygen, minerals, and water� In addition, most of the pest and disease factors in a soilless substrate are avoided�
Overall, hydroponics and soil growing are not different with regard to the needs of the plants� The chemistry behind hydroponics is not different from soil growing with regard to providing ideal levels of nutrients to the plants� Only the procedures and some sources of nutrients differ� With soil we like to use slow-release compounds that will not rapidly pass beyond the roots of the plants, whereas in hydroponics we want highly soluble compounds that will dissolve completely in water because the nutrient solution is applied directly to the plant roots� The chemistry is the same for the plants as they must actively take up the same nutrients and water from the soil solution of the soil, or from the nutrient solution in hydroponic culture�
The principal difference between soil and hydroponic cultivation is this precise management of the availability of the essential elements to the plant roots under hydroponics� The other techniques in the care of the above-the-ground portion of the plants are similar in both hydroponic and soil cultures� All aspects of plant training, pest and disease control, even watering by a drip irrigation system also apply to soil culture� One step further is to extend your growing season by the control of environmental factors such as temperature, light, carbon dioxide, and relative humidity through greenhouse growing� You may grow either soil or soilless in the greenhouse, but normally it is advantageous to use hydroponics under controlled environments to maximize the health and yields of your plants�
