hatchery operations 97 



Table 11. composition of several organic fertilizer materials, (source: 

 snow et al. 1964.) 



"Calculated by dividing protein content by 6.25. 



ORGANIC FERTILIZERS 



Organic materials such as composted plant residues, manure, stable 

 drainage, slaughterhouse waste, and municipal sewage are very good 

 sources of nitrogen. They also contain a large percentage of organic carbon 

 as well as other minerals in small amounts. Typical analyses are shown in 

 Table 11. Values may vary slightly depending on the conditions under 

 which the crops were grown or the products were processed. 



Organic fertilizers are recommended for only fingerling fish production 

 to accelerate the production of zooplankton in rearing ponds, particularly 

 in new or sterile ponds. Their use is limited by cost and labor requirements 

 for application. The advantages of organic fertilizers are their (l) shorter 

 cycle for plankton production than inorganic fertilizers, (2) decomposition 

 to liberate CO^, which is used by plants for growth, (S) aid in clearing 

 silt-laden waters, and (4) use as a supplemental feed. 



Their disadvantages are that they (l) are more expensive than inorganic fer- 

 tilizers, (2) may deplete the oxygen supply, (3) may stimulate filamentous 

 algae growth, and (4) require more labor to apply than inorganic fertilizers. 



