424 Fortieth Annual Meeting 



COMMERCIAL FERTILIZERS FOR PONDS 



If agricultural lands are treated with lime, Thomas-meal, 

 kainit and saltpeter, then the cultivated plants can by means 

 of their roots get lime, phosphoric acid, potash and nitrogen 

 from the soil and grow luxuriantly. In water culture the 

 biological process is somewhat different. In this case the 

 plant food is taken up and elaborated by sundry species of 

 algae, especially the one-celled algae that are in suspension 

 in pond water, and serve as excellent food for the minute 

 creatures that constitute the food of carp. These algse have 

 no roots and are therefore not able to extract plant food 

 from the bottom of the pond. The swimming algae get 

 their nutrition from the water, and so the fertilizers to be 

 used in pond work must be soluble in water. 



As Thomas-meal contains phosphoric acid soluble only in 

 citrates it is not available for water- fertilization. In the 

 above-mentioned experiments the fertilizing of the potash, 

 nitrogen and lime become available only so far as the soluble 

 acid already naturally present in the water suffices for the 

 growth of algse. Instead of Thomas-meal let us in pond- 

 culture use superphosphate which is decomposed by means 

 of sulphuric acid. In such superphosphates the phosphoric 

 acid is present in a form soluble in water, so that this plant 

 food can be extracted from the water and appropriated by 

 the algae. We might also get water-soluble phosphoric acid 

 in decomposed Peruvian guano. This contains, besides 

 phosphoric acid, also nitrogen, lime and some potash. It is 

 quite high in price and can without waste of the precious 

 nitrogen, only be used in such ponds as have little or no 

 humus. Some years ago in some poor ponds of this sort, 

 after first liming the pond-bottoms, I used Peruvian guano 

 with an addition of salts of potash, with entire success. 

 That was a complete manuring, in which the leading plant 

 foods were furnished in sufficient quantity for an enor- 

 mous development of the suspended algse. In most ponds 

 water-soluble phosphoric acid is present in too small quan- 



