with respect to food chains may also influence the selection of fertilizers « 

 Fertilizers are often mentioned in the literature for specific conditions 

 and areas (as Swingle and Smithy 1950j Meeheanj 1939)- 



Fertilizers are generally applied in the spring of the year when 

 waters grow warm and biological activity increases, European consensus 

 (Schaeperclaus^ 1933| Lawson, 19375 Wiesner, 1937) is that a single large 

 application of fertilizer suffices, and that additional doses are super- 

 fluous o American opinion (exemplified by Swingle and Smithy, 1939a., 1950s 

 Zellerj 1952) is that frequent^ light doses result in higher producti^'/ity 

 and improved conditions. The lack of agreement stems from differences in 

 practice and is significant mainly in fertilizing shallow waters = European 

 fish-cultural methods place greater emphasis on liming (see Fertilization 

 and Pond Culture) and the role of the bottom in pond productivity. Both 

 factions recommend an even distribution of fertilizers over shallow areas. 

 Most fertilizers are dry solids and are distributed as such by broadcasting. 

 Smith (1933), in using this method, produced rapid plankton growth, but a 

 larger total yield resulted when the fertilizer was dissolved from suspended 

 sacks. This possibly may be an important consideration in situations where 

 nutrients are "lost" in the bottom. If a fertilizer consists of several 

 substances, all should be added simultaneously (except caustic lime) to 

 insure proper chemical interdiction (I'fi.esner, 1937) » 



The theoretical approach of nutrient liberation has been considered 

 by Hasier and Einsele (19U8) for the activation of phosphate in eutrophic 

 lakes. It is based on the dissociation of phosphorus and iron and their 

 mutual sedimentation as FeP(l at the fall overturn. Two schemes were pre= 

 sented for the rerrcval of ferrous iron. One is the precipitation of 

 ferrous ions with sulfatej amounts of calcium sulfate needed and the ensijing 

 reactions were discussed. Implications of other nutrient liberations are 

 given by Welch (1935) j who noted that magnesium may free calcium and that 

 sodium may release potassium. The cultural practice of draining ponds 

 mobilizes nutrients in accordance with this concept. Since productive 

 increases result in the reduction of bottom soils, draining and aeration 

 cause the oxidation of bound nutrients which, in turn, makes them available 

 the following season. Nutrient release is also one of the major functions 

 of liming (see Fertilization and Pond Culture) o This concept holds that 

 chemical elements are limiting, not because of their absence or paucity, 

 but because of their inability to contribute to anabolic processes. It is 

 an approach to artificial fertilization that may be wort.hy of greater 

 consideration. 



Interpretation of Results 



Fertilizers act to increase the general productivity of water,, The 

 first and most pronounced effects of these nutrients appear on organisms 

 having short life cycles (Ball, 19U9) . Fish are last to indicate benefits 

 of fertilization, and the quantity produced is the ultimate measure of 



15 



