Such ideal conditions are, however, hardly attainable. For this it would be neces- 

 sary to have a sure knowledge of the experimental results in advance. Only then could the 

 stock be adequately formed. In order to eliminate every inequality between the experimen- 

 tal ponds and the results of unequal stock densities it must be a prerequisite for every 

 fertilization experiment to have: — equal stock density in all ponds, equal inset piece 

 weight, uniform species, equal hereditary factors of the experimental fishes. Experi- 

 ments with different stages of stock are not usable. The success of fertilization experlwente 

 undertaken according to these rules, of course, does not entirely correspond to what will 

 be obtained later in practice with equal fertilization and increased fish stock density, 

 but in order to have scientific accuracy the lesser evil must be chosen. Demoll and 

 Walter rightly advise that for experimental fishes, at least a part of them should be 

 yearling carps (naturally an equal percentage in each pond) and not two-year carps ex- 

 clusively. The yearling carps on account of their great growth capacity yield better 

 utilization possibilities. 



It is to be observed in fact that fertilization experiments under practical con- 

 ditions and due in part to disregard of these rules show unsatisfactory results. Fre- 

 quently there are further, especially secondary appearing factors, which are stronger 

 than all fertilization actions. A descriptive example of this has of late been offered 

 by experiments published by Goepfert, and by many other cases. 



The great advantage of fertilization with mineral substances is because it has made 

 possible larger scale fertilizations in the pond also, and from a metabolic physiological 

 viewpoint, only those substances which occur in minimum are added to the metabolic cycle. 

 Naturally, however, the yield cannot be arbitrarily increased by supplying a substance. 

 On the contrary presently a second, third, fourth primitive foodstuff or even the light 

 and heat factors go into minimum. The purpose of the fertilization experiments of the 

 practical pond manager is to make determinations on local conditions in this regard. 



Another method to determine the fertilization requirement of the water, is the beaker 

 method of productivity appraisement, which I will mention at least briefly here. Ferti- 

 lisers of different kinds and of different concentrations are added to various beakers 

 which are filled with water samples inoculated preferably with growing algae. After about 

 10 to 20 days determinations are made as to the amount of algal growth (important to the 

 metabolic cycle) which has developed on inset glass plates (compare Lundbeck). The glass 

 with the strongest growth development shows the most favorable fertilizer addition. In the 

 beaker appraisement it is to be noted further that, in accordance with Sachsenhausen ex- 

 periences, potash above all promotes plankton plants. The effect of potash will perhaps be 

 most evident by a general green coloration if there has been a simultaneous inoculation 

 with suspended algae. The glass beaker appraisement is seldom used by the practician. 



In the application of fertilizer in Sachsenhausen the most frequent possible ferti- 

 lization was striven for, in order to continually fill up the foodstuff reserve and to 

 counteract undesirable denitrification when nitrogenous fertilizers were distributed. 

 After it was recognized that the fertilizer is absorbed by the soil (as also taught by 

 agriculture), and from there is gradually given off at places where it is consumed, and 

 that many fertilizers must simultaneously fulfill important functions in nitrogen fixation, 

 in the improvement of bottom mud, and in the decomposition of nutritive substances, it was 

 rightfully required that the fertilizer be given in one dose. This method is also cheaper. 

 The finely divided fertilizer had best be strewn out on the dry pond floor shortly before 

 it is covered with water, or if better distribution is desired it may be distributed from 

 a boat into the water immediately after water coverage. Reeded ponds remain free of 

 fertilizer. 



Lining is, as I again emphasize. Just like the regular elimination of over-water 

 plants, the most important provisions for a good reaction of the mineral fertilizers 

 dealt with in this chapter. The most profitable fertilization as already stated is always 

 a fertilization with phosphates. This is particularly the case in lime rich ponds with 

 good rotted mud. With clean sandy soil and water rich in combined phosphoric acid, 

 phosphate fertilization reacts just as feebly as liming as an increaser of production. 

 So far as we know today the approximately equivalent fertilizers in preponderant consider- 

 ation are: Superphosphate containing about 16 to 20 percent water soluble, Rhenania 



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