Table 9. 



Shewing the calcium oxide rate and contents in organic substance 

 of the soil of three neighboring ponds rith like v/ater supply. 



Size of . Loss on ignition ofSrsoS^^ ''^^^^^ ^"'^^^^ ^° 



ixze 01 2^^^ bottom^ i of * carps. Kilograms 



I»o. pond in conditions of /'o^l^oni, > ol (jaO percentage ner hectar Iver- 



hfictar conditions ^he dry weight ^^ ^ „^ per hectar. Aver- 



u± oiic Lujr gg Q^ several years, 



weight". ' 



These ponds, up to then had been neither fertilized nor chalked, nor had the fish 

 been fed. 



In hatcheries with occasionally sour v;ater (as predominating in Lower Lusatia, for 

 instance), the calciujn content of the soil is very low, often niuch below 1 percent. It 

 is difficult to say hov; far the layers of detritus mud are of importance for the absorptio: 

 and adsorption of nutritional matter. It is also difficult to say to what extent these 

 layers of mud offer shelter to aquatics and to what extent they are merely end-products, 

 i.e. an index for high productivity. 



It must be denied — although it is an ever recurring assertion — that the adsorbing 

 and absoAing activities of the bottom mud are definitely proved by the fact that phos- 

 phatic fertilizers shov/ strong after effects through the following years. It is also 

 quite possible that especially valuable organic mud forms during the first year but is 

 utilized to its fullest extent only in the second and succeeding years (by mud dwellers 

 or through very rapid decon^osition and re introduction into the metabolic cycle). 



On the ct.her hand, the investigations of Lantzsch (according to Demoll, 1925) have 

 demonstrated the importance of the bottom mud as a bottom "laboratory" of the nitrogen- 

 fixing bacteria. 



But whatever the case, the presence of an easily decon5>osing, organic mud, rich in 

 colloids 7d.ll best guarantee the maintenance of a relatively high productivity. 



In connection with this, we emphasize again the exceedingly strong influences of 

 the different species of pond flora, of the noxious effects of the coarse, slightly 

 decomposing cellulose mud, and of a bottom over-run with the roots of sxirface plants. 

 The species mentioned will eliminate the activity of the fine colloidal mud in every 

 directicwi. 



In order to preserve the characteristics and productivity of tlie mud — so important 

 for the fishbreeder — ^we alternate betv/een periods of mud producing (trophogenic) 

 cultivation and periods of mud-decomposing, i.e. mineralizine (tropholitlc) drainage 

 of ponds. This procedure forms — as so often emphasized, the essential basis of rational 

 pond culture. 



At this opportunity, naturally the water holding power of the bottom, its workabil- 

 ity, and many other production biological factors are indirectly of importance. A sawing 

 of the pond floor, the production of a plant formation during the dry period, which may 

 be carried out at the time of cultivation, accelerates the drying of the mud covered 

 bottom and thereby the mineralization and production power. 



60 



