1. Field of the Invention
This invention relates to compositions and methods for use in aquaculture. More particularly, it relates to methods employing controlled release fertilizer compositions to release nutrients into closed aquatic ecosystems such as ponds, lakes, watersheds and other aqueous environments in order to enhance the growth of phytoplanktonic algae populations in the water and to thereby promote marine life populations.
2. Description of Related Art
Fertilization has been recognized heretofore as being an important technique in management of closed aquatic ecosystems such as ponds, lakes, watersheds and the like, particularly for purposes of stimulating the growth of phytoplanktonic algae in the water. Such phytoplanktons serve as the basis of the food chain in such aquatic environments and are, therefore, necessary for increasing fish production in these closed aquatic ecosystems. In addition, proper fertilization techniques have been shown to serve several other useful functions including limiting the growth of troublesome aquatic weeds in the closed aquatic environment and improving water quality.
For most freshwater ponds and lakes, phosphorus is considered to be a key nutrient in fertilizers, but inclusion of nitrogen and other nutrients in the fertilizers has been recognized to be desirable. However, phosphorus is the limiting nutrient for development of phytoplanktonic algal blooms. Thus, most ponds require frequent addition of fertilizers rich in phosphorus to maintain good phytoplankton blooms throughout a production cycle. Frequent fertilization with phosphorus is needed because available phosphorus is quickly adsorbed by pond muds or taken up by phytoplankton. Once adsorbed onto pond muds, little phosphorus is released back into pond waters, because the oxidized water-mud interface acts as a barrier between mud and overlying surface waters.
Pond and lake fertilization has undergone several stages of development over time. Recently, these changes have resulted from attempts to reduce the rising cost of fertilization and to respond to concerns relating to the effects of fertilizer on the environment.
In early fertilization programs, granular N-P-K fertilizers such as 8-8-2 or 20-20-5 compositions were simply broadcast over shallow areas of ponds, or poured from a boat along the shallow water edges. Later research demonstrated that placing fertilizers on an underwater platform produced similar results, required less fertilizer, and was less time-consuming. Wind and wave action were found to distribute nutrients throughout the pond and to make them more readily available to phytoplankton rather than tied up by pond muds. A single, well-placed platform could service a pond with up to 6 surface hectares (ha) of water. Subsequent findings indicated that ponds with a history of fertilization required only phosphorus fertilization and costs could be substantially reduced.
Despite the proven performance of fertilizer platforms, few pond owners used platforms in actual practice. Probably the biggest breakthrough in the use of fish pond fertilizers came in the form of liquid fertilizers. Besides the superiority of liquid fertilizers over granular fertilizers in increasing fish yields, liquid fertilizers had several other attractive attributes. Liquid fertilizers which are almost totally soluble in pond or lake water if properly applied could be used effectively at reduced application rates relative to prior granular products, were relatively easy and safe to apply, and were relatively economical to use.
Thus, it has been known previously to apply common, soluble fertilizers to ponds and lakes in order to increase inorganic nutrient concentrations, to favor greater phytoplankton growth and to ultimately enhance production of fish and/or crustaceans in the aquatic ecosystem. Current practice involves the use of liquid fertilizers or common, soluble granular fertilizers such as urea, ammonium, phosphates, ammonium polyphosphate, potassium sulfate and the like which are applied to closed aquatic ecosystems such as ponds and lakes throughout a production cycle. Frequent applications are required to keep the nutrients available in solution.
However, the prior art techniques have been unable to overcome problems presented by the need for constant availability of nutrients for growth of phytoplanktons and the fact that the previously proposed fertilizer products for use in aquaculture have provided nutrient availability for only a short duration of time after application. Accordingly, it has been necessary heretofore to apply such fertilizers up to 8-10 times per production cycle in order to maintain uniform phytoplankton growth within a given closed aquatic ecosystem such as a pond or a lake. If such an application schedule is not followed, it has been found that fish production in the environment suffers. Of course, such repeated application schedules are expensive, inefficient and time consuming.
Thus, the use of inorganic granular fertilizers in aquaculture has been considered to be costly and inefficient because of rapid dissolution of most fertilizer materials and leaching into the aquatic ecosystem and the inability to utilize nutrients efficiently.