The Influence on Rate of Growth of Transferred Plants in Hydroponic Systems Compared to Soil

ABSTRACT

        The purpose of this experiment was to establish if there was a difference in growth rates between plants transferred to hydroponic systems when compared to those transplanted to soil.  Four different plant species were used in this study.  Each species of plant was transferred from soil into two indoor hydroponic systems and two soil systems.  Substrates were varied in each system.  In each system substrates’ were assorted as follows: the first hydroponic system (H-1) Hydroton clay substrate, the second hydroponic system (H-2)  had a Hydroton clay/barley straw substrate, in soil system (S-1) a soil bat guano/horticultural charcoal mixture, and last soil the control soil (S-2).  Each plant’s overall appearance and color was recorded to compare health of the plant in each system.  Plants in each system were measured on a weekly basis and data was compared after three weeks of growth.  An ANOVA single factor test was used to determine if there were statistically significant differences in growth rates among each plant species.  The results concluded that there are no significant differences in the growth rate between hydroponic and soil methods of indoor cultivation for onion chives (Allium schoenoprasum), parsley (Petroselinum crispum), tabasco chili peppers (Capsicum frutescens), and yellow bell sweet peppers (Capsicum annum).

INTRODUCTION

        Hydroponics is the cultivation of plants in a nutrient enriched aqueous solution without the use of soil.  Hydroponic systems require the use of water as a primary resource for roots to uptake nutrients.  In hydroponic systems there are many different types of mediums or substrates that are used; however their purpose is to provide a soilless alternative in which plants can grow.  With the use of hydroponic systems, vegetables and other plants can be grown year round.  Adhering to seasonal growth times of   many varieties of vegetables and fruits becomes unnecessary.  These nutrient rich foods can be more easily accessible with a space saving, hydroponic home garden.  Another added benefit to hydroponic systems is that expensive plants, such as water lilies, can be transferred from outdoor ponds when temperatures drop to indoor water based systems.  This transplanting method is a form of “overwintering”.  This technique keeps these plants growing until they can be transplanted back to the pond in warmer months (Dunn, 1997).  

Hydroponic gardens can be indoors or outdoors.  Hydroponic systems do not have to adhere to traditional seasonal growing of plants.  The use of indoor light-emitting diode (LED) bulbs, compact fluorescent lamps, high intensity discharge (HID) lamps, or simply placing the system in a sunroom or outdoors with natural sunlight can keep hydroponic plants healthy (Patten, 2008).  Transferring outdoor plants to an indoor hydroponic system before cold months arrive can save a crop, thus increasing yields.  The quality of fruits and vegetables can be improved by allowing growers to add and regulate nutrient amounts used in hydroponic solutions.  Plants grown in hydroponics often have better quality and higher yields when using the same amount of water as compared to traditional soil methods (Rouphael, et. al. 2004; as cited by Azad et. al., 2009).  Re-circulating, dripping, or misting plants with nutrient enriched water solutions conserves fertilizers, and water, requires less energy, and decreases waste (Magan et. al. 2003; as cited by Azad et. al., 2009).  These methods give the hydroponic indoor farmer more control of the conditions for their plants, water sources used, added nutrients, and cleanliness.  Using hydroponics requires a fraction of the amount of water required in soil systems (Bradley and Marulanda 2000; UNDP, 1996; as cited by Azad et. al., 2009).

Hydroponic systems are economical and recycle water before it is disposed as runoff.  This is the case in recovery, or closed, hydroponic systems.  A closed hydroponic system is also known as a nutrient recovery system.  In the closed system the nutrient enhanced water is re-circulated.  A plant requires carbon, oxygen, hydrogen, which are acquired from the air and water.  Additional nutrients are required for plant growth in the form of macronutrients and micronutrients.  The macronutrients that are considered primary nutrients for a plant to sustain growth are nitrogen, phosphorus, and potassium.  Micronutrients, and secondary nutrients include: magnesium, zinc, calcium, boron, chlorine, cobalt, copper, iron, manganese, molybdenum, selenium, silicon, and sulfur (Patten, 2008).  There are various models of hydroponic systems that are considered “closed”, such as deep water culture (DWT) and top-feed buckets (Patten, 2008).  Nutrient film technique (NFT) is another method of closed hydroponics.  This method delivers a constant nutrient rich flow of solution to the root system.  This nutrient enriched solution drains down through the substrate and is delivered to the roots.  Nutrient solute is then air pumped back up through drip tubes recycling the solution over growth media.  This is a re-circulating drip irrigation system that requires pH regulation and mixing of nutrients in the water solution after it has been recycled by the plants.  This recycling by the plant changes the pH of the solution; therefore it must be changed at a suggested seven to ten days with a fresh nutrient solution (Patten, 2008).  A pH meter is placed in the solution and regulated at pH 5-6 for optimum plant growth conditions.  This closed hydroponic (NFT) method was used in a pH-buffer nutrient treatment experiment by (Azad, et. al., 2009).  

Another type of hydroponic system is called an open hydroponic system.  The delivery of nutrients in open systems is similar to a closed hydroponic system because the plants are given nutrients via irrigation systems.  The difference is often in model design.  Open hydroponic systems contain runoff after the nutrient solution is delivered.  There is no recirculation of solute.  The nutrient solution is mixed and delivered fresh every time plants are watered.  This is in contrast to closed systems, where the solution is circulated and changed less frequently.  Close monitoring of pH is essential in any hydroponic system closed or open.  “In hydroponics, the nutritional quality of a nutrient solution is limited by water quality… the control of pH is important to plant growth” (Bouchra, 1998; Robert, 2006; as cited by Azad, et. al., 2009).

Substrate used for hydroponic systems has to be chosen for its specific characteristics.  The media must have excellent water holding capacity.  The term substrates used is the same as the term media when searching for soilless systems.  The media has to serve as a growing environment but also have airy interstitial pockets to ventilate plant roots.  Aeration to roots is essential to the plant’s survival. “Good air properties are especially advantageous in the growing of epiphytes” (Kleiber and Komosa, 2010).  There are many different varieties of substrates to use in hydroponic systems to include: coco coir, perilite, rock wool, rocks, expanded burnt clay pellets, and more varieties.  Rock wool is often used in plug or pellet form when sprouts are transferred (Patten, 2008).  In Poland the common, inexpensive growing media used for the cultivation of Birdsey (Anthurium cultorum), is expanded clay pellets, and polyphenolic foam (Komosa and Kleiber, 2003b; as cited by Kleiber and Kimosa, 2010).

Expanded clay pellet substrate is made from burnt clay.  This medium is not only cost effective, but it also has very stable properties.  This type of substrate is reusable and has excellent aeration properties. Proper cleaning between uses of clay media prevents formation of microbes in water, pH imbalances of water, and allows reuse of substrate.  Coco coir (coconut fiber) has excellent water holding capabilities and can be mixed with soil and clay pellet substrates (Patten, 2008). Substrates that have poor aeration qualities and may clog a hydroponic system would be sand and fine gravel.

Hydroponics have a lot of advantages.  A hydroponic system is more environmentally friendly and requires the use of less energy in comparison to traditional soil methods (Bar-Tal, 1999; as cited by Azad, et. al., 2009).  The primary advantage is that it puts the grower more in control of what additives are introduced during plant growth.  Insecticides and pesticides are typically found on outdoor soil crops and have been found to be hazardous to humans and animals.  Managing what chemicals, macronutrients and micronutrients are used to supplement the de-chlorinated water and sprayed onto foliage is of importance to hydroponic gardening (Patten, 2008)

There are also disadvantages of hydroponic systems which include growth of algae in water, mites on plants, and maintaining pH regulation.  These can be regulated with automated timers, nutrient regulators, antimicrobials, algaecides, scheduled tank cleanings, ultraviolet lamps, and filters that control algae.  Algae can invade hydroponic clear tanks that are in direct light.  Algae need moisture, nutrients, and light source to grow.  A method of darkening containers that are in direct light is often used to prevent algae growth.  This can be done by painting the outside of container with spray paint or covering container to omit light source from penetrating container (Patten, 2008).  There is a higher risk of root-borne pathogens spreading in re-circulated closed hydroponic systems than in open systems.  Prevention of diseases to plants can be done by UV radiation, slow filtration, pasteurization, and draining of the nutrient solution before re-circulation (Bergstrand, et. al., 2011).  One of the disadvantages is the cost factor of the media, such as coir, vermiculite, and other substrates.  There are alternate media that work just as well if not better than traditionally used media.  Some countries do not have access to more expensive growth media, and are using byproducts of industry as media that would otherwise have little economical use. The use of more economical substrates is on the rise (NeSmith and Duval, 1998; as cited by Navindra et. al., 2011).  

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