or commercial mixtures expressed in percentage ratios of nitrogen iphos- 

 phorusspptassium (N:P:K) . There are also mineral fertilizers such as 

 superphosphate which contain several minor elements in addition to soluble 

 phosphorus (table 1) . 



Since the compositions of inorganic fertilizers are known or easily 

 determined^ they are especially adaptable where definite quantities of 

 nutrient elements are to be applied. Swingle (19^7) found that large 

 amounts of phytoplankton grew in response to inorganic fertilization by 

 virtue of the rapid solubility and distribution of the nutrient substances, 

 but that carbon dioxide was limiting in ponds fertilized only with inorganic 

 materials. In Japanese rice-paddy carp culture^ Hiyama (1950) concluded 

 that organic manures promoted more zooplankton than inorganic fertilizers. 

 Organic and inorganic fertilizers have been successfully used in combination 

 in many instances. 



The following list^ adapted from Lavjson (1937), shows the relative con- 

 sumption of different fertilizers in Czechoslovakian pond culture for 1935|* 



Lime and limestone , .o„ ... o o „ 1,579 metric tons 



Superphosphate , , . , , . , = « . . . 301 '' " 



Other inorganic fertilizers. . , , , . 86 " ■' 



Manures. ...,,....»..=,. U63 " " 



Compost and aqUatic plants ...... 8^0 " " 



If such a tabulation Xifere available for fertilizers used in this 

 country, it would undoubtedly show a greater relative consumption of super- 

 phosphate and other inorganic fertilizers^ plus large quantities of meal 

 residues. The world-wide use of either mineral or organic fertilizers is 

 largely a matter of availability. Large quantities of meal and mineral 

 fertilizers are manufactured and thus available in this countrj'^, while 

 Asiatic fertilization (Mora, 1950| Rabanal, 19^0) is limited mainly to the 

 use of locally occurring manures and other organic substances. 



Local and regional differences occur in the chemical composition of 

 water and soils. For this reason the selection of fertilizers should be 

 based on the results of chemical analysis of water and soil (Rabanal, 1950s 

 Rounsefell and Everhart, 19^3: Schaeperclaus, 1933) . An alternative or 

 supplementary method of determining fertilizer requirements is suggested 

 by Schaeperclaus (1933) . It consists of inoculating containers of parent 

 water, enriched by various kinds and concentrations of fertilizers with 

 algal cultures. Highest j.;rowth rates indicate the most suitable fertilizer 

 and concentration. Swingle and Smith (1939a) used this method with ap- 

 parent success in early experiments. It has obvious limitations since 

 environmental conditions cannot possibly be duplicated in culture containers. 

 Hasler et. al. (19^1), for instance^ found that the actual lime requirement 

 for the alkalization of a bog lake was 'Tiore than three times the quantity 

 estimated by sample inoculation. Availability, cost, and mode of action 



Hi 



