I finally auggest for conpreheneiveness, that the pond manager In the first tangible 

 fertilization experiments to determine fertilizer action, should proceed as follows. In 

 order to correspond to field fertilization experiments in agriculture, ponds as much alike 

 as possible and with absolutely similar stock must be used. Therefore the follcwing fer- 

 tilization plan is taken as a basis > 



Pond I. Unfertilized. 



Pcaid II. ^ kg ha (35.6 pounds per acre) of P2O5 (pure phosphoric acid) as 

 super-phosphate, Thomas meal, dicalclum phosphate or Rhenania 

 phosphate . 



Pond III. Fertilization as in II plus 50 kg ha (^.5 pounds per acre) of K-O 

 (pure potash) as No. ^0 potash fertiliser salt, potassium-nagnesium 

 sulphate or Kalnlte. 



Pond IV. Fertilization as in III plus 5 to 10 dz ha (M5 to 890 pounds per 

 acre) of CaO as burned lime, limestone flour or calcium carbonate 

 marl. The lining should be done in the autumn. 



All experimental ponds must be kept tree from excessive over-water plant development. 



Experiment IV obviously can only be started if lining in all ponds has not already 

 become necessary on account of a very low A.C.V. , and in accordance with the fundamental 

 rules given In Chapter VIII. It can be replaced if necessary by an experiment using 50 

 kg per hectare (^4.5 pounds per acre) of nitrogen. The foremost rule operating in the 

 setting up of the fertilization plan as well as in all scientific experiments is the 

 followingt In every new experiment only one factor may be changed, otherwise no com- 

 parison of results will be possible. Although this fundamental law is quite obvious, it 

 is repeatedly left out of consideration. 



I have puirposely chosen relatively high, the quantities of fertilizers given in this 

 plan for reasons of safety and for psychological reasons because of the danger that in 

 first time fertilization a certain reserve fertilization must be undertaken. Later 

 experiments can then show to what extent these quantities can be lowered. 



If it is first determined by the experiments that a natural growth increase of about 

 30 to 100 percent occurs as in other places, then In the practical evaluations in fertiliaed 

 ponds are to be based on a correspondingly higher natural increase, of natural increase plus 

 fertilizer increase. In other words, the number of fishes to be set in is to be so In- 

 creased that their piece increase remains the sane. 



H. Organic PBrtilization . 



The organic fertilization carries into the pond almost all of the foodstuffs which 

 ar« required in the metabolic cycle. The introduction of the organic mass can simultane- 

 ously act to improve the soil. Many fertilizers also increase the freely suspended 

 detritus and the quantity of bacteria in the water. So long as the water is not over- 

 loaded with detritus, the nutrition for animal plankttxi (especially Daphnidae) is also 

 directly increased thereby. PBrtilization experiments of Naumann (according to Walter, 

 1922) and of Jaemefeld under completely comparable experimental conditions in half vats, 

 have shown that nitrogen free pond fertilization with phosphates and potash, and indeed 

 with completely nitrogen free cellulose, leads to a high production. The details of 

 the further favorable action of the organic fertilization in the pond have not as yet 

 been clarified. 



The extremely advantageous effect of the organic fertilization upon the growth 

 increase of fishes is shown by a fertilization experiment by Probst with perished sub- 

 merged water flora (predominantly pond weeds). In ponds which were fertilized with 30 kg 

 of P2O5 per hectare (26.7 pounds per acre) a yield increase of 50 percent, and by the 

 addition of a double quantity of plants (the total amount was increased about four fold), 

 an Increase of 100 percent was obtained. In Wielenbach in 1927, 10 loads of manure per hectare 



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