G. Fertilization with Commercial Phosphate . 

 Potash and I<ltro.p;enous Fertilizers . 



The artificial fertilization with commercial mineral phosphiate, potash and nitrogen- 

 ous fertilizers has above all the purpose of increasing the utllizable quantities of 

 minimun occurrLnc primitive foodstuffs vfhich in the final analysis control t he level of 

 production of fish flesh, as has been shown in Chapter 1. The introduction of fertilizers 

 into the metabolic cj'cle of the pond increases the natural nutrition of the pond fishes, 

 just like any other of the. above-mentioned methods of pond care. At times this occurs by 

 means of growth, at other times by the mass development of plcint plankton visible by the 

 clouding and green coloration of the entire water, and this again promotes the nutrition 

 of the flora and bottom fauna. In this way fertilization is especially valuable for the 

 pond industry, for as I repeatedly emphasize, the natural nutrition in the carp fishery 

 is the basis for a profitable feeding. Natural nutrition can never be completely re- 

 placed by other foodstuffs. In trout culture the natural nutrition Is indispensable 

 for the production of usable spawning trout. 



Experiments on the action of artificial fertilizers were principally and almost 

 simultaneously started for this purpose in the experiment stations at Wielenbach and 

 Sachsenhausen, Naturally in spite of this, a great many questions are still unclarified. 

 This is inainly for the reason that further experiments in practical pond fisheries have 

 mostly had to combat extraordinary difficulties. 



The water in 'Wielenbach has an A.C.V. (acid combining value) of about 2.5 to ^ cubic 

 centimeters of N hydrochloric acid per liter, a potash content (K2O) of 1,5 to 2.2 milli- 

 grams per liter and a phosphoric acid (P2O5) content of 0.C12 to 0.06- milligrams per 

 liter. The soil consists mostly of top layer 20 an. thick humus soil, under this a 30 to 

 4.0 cm. layer of whitish green marl, and then 40 cm. of loam. In Sachsenhausen, an A.C.V. 

 of 2.0 to 2.8 cc of N hydrochloric acid per liter, a potash content of 1,1 to 3.0 mllll- 

 graras per liter, and a relatively much blither phosphoric acid content, namely 0.25 to 0.8 

 milligrams per liter was determined in unfertilized pond water. The extremely permeable 

 soil consisted, according to Zuntz, of sand with a thin layer of humus brown pond mud 

 and in greater depths of moor. These special regional soil and vjater conditions liave 

 therefore been taken from the Sachsenhausen and Ti'ielenbach experiments as a basis for 

 conclusions. 



The conclusions therefore cannot have a direct general validity from purely theoretical 

 considerations. In the largest German pond fishery districts more or less different con- 

 ditions are present. Scientific experiments by Jaemefeld have likewise shown that in 

 different quality conditions, one and the same fertilizer combination gives various results. 

 For these reasons the pond manager in considering his own soil and water conditions cannot 

 avoid fertilization experiments if he wishes to detennlne which main nutritive substances 

 ■vdll act favorably in his ponds and call forth a good revenue. 



Pond fertilizing experiments must be extremely or critically conducted, even If thej' 

 serve exclusively practical purposes in one's own fishery. Unfortunately, many experiments 

 have been undertaken without a knowledge of the influence of unequal fish stock density. 

 It is possible that many older experiments could not stand a critical consideration in 

 this direction. 



It is fundamentally required in pond fertilization experiments that completely 

 isomorphic and equally fertile ponds which have been operated at least three years, be 

 compared. Simultaneously fertilized and non-fertilized ponds must be available. No 

 feeding must be done. The natural growth increase during several years, if possible, 

 should be known for all experimental ponds. The experiments are to be conducted as simply 

 as possible. 



The results of fishing out would best reflect the true fertilization success if all 

 the fishes had equal normal piece grovrth and equal fishing out weight, which is striven 

 for in practice. If this condition could be fulfilled, a combination of fertilization 

 experiments with feeding could be very instructive. 



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