Also all other control methods suggested up to now, such as fertilizing irtth liquid 

 manure, shading by boards or ash (trees), liming vidth 10 to 20 percent milk of lime 

 shortly before water covering have their great faults and often even contrary action. 

 It may, however, be said that clear water, especially spring water, and prolonged water 

 coverage favor the development of the filamentous algae. As in every combat against water 

 plants, it must not be forgotten with the filamentous algae, that only an excess is injur- 

 ious and to be removed. In evej-y plant development in the pond, the measure of occurrence 

 primarily determines the usefulness or injury. 



E. Drainage and Cultivation of the Pond Bottcni o 



Rational care of the pond bottom aims to ameliorate its biological processes and to 

 "interfere" in the metabolic cycle of the pond from the viewpoint of better productivity, 

 that is, a possible and desired increase in profits. Bottom culture chiefly aimas 



(1) To create a fertile, fine-colloidal and absorptive organic mud, leading 

 to a gradual reduction, that is, mineralization of all excess mud, 

 especially of the indigestible cellulose mud. 



(2) To destroy the web of roots of surface plants, which cover the bottom and 

 irtiich fonn a blind alley to the normal course of the metabolic cycle. 



The conditions named in (1) can easily be achieved through drainage of the pond and 

 exposure to winter frost. This will lead to a gradual mineralization of the accumulated 

 layers of mud and an amelioration of same along the lines, mentioned previously and 

 following . 



Spading and ploughing of the top layers of the bottom will aid the process still 



further. 



Unfortunately the aims in (1) and (2) may not always be achieved by one and the 

 same method of soil cultivation. The destruction of surface plants, for instance, re- 

 quires deep ploughing which will of course bring about the ploughing under of the 

 fertile, upper layers of the mud, while the sterile, inert mud of greater depth will 

 be brought to the siu'face. The achievement of the first aim meanwhile permits only the 

 cultivation of the uppermost active pond-bottom layers which are often extraordinarily 

 thin. Othemise the soil cultivation as such could not be worked out valuably in a 

 production-biological sense. 



Finally, the care of the pcmd bottom also has a third aim; the providing of good 

 hygienic conditions. By means of the draining, disease germs and infected intermediate 

 hosts of disease instigators resting upon the bottom should be destroyed. The reduction 

 of gradually accumulating masses of mud in fertile or reed infested ponds decreases the 

 possibilities for the occurrence of diseases. In the trout-feeding pond their view- 

 points even step exclusively into the foreground. 



The draining of the pond bottom, which is comparable to fallowness, takes place 

 today only in the winter until March or April or with brood ponds even up to July. 

 This is spoken of as "wintering". The draining during the summer also called "summering", 

 is customary in only very few fish industries. There are, however, individual, often 

 large industries, which ever/ year alternately "summer" approximately 50 percent of 

 their ponds. Or a pond in the first year is covered in spring, planted in the second yeer 

 with lupine which is turned under in blossom in July as the pond is then to be used as 

 a "brood nursery pond". In the third year potatoes or oats are planted and harvested, 

 that is, the "summering" is done throughout the summer. With this crop rotation, the 

 total yields according to experience are often higher than by flooding over every year. 

 By means of the agricultural utilization, the suppression of weeds is of especial 

 advantage. In a Holland pond industry, the ponds after a utilization of seven years, 

 are then planted in one year with oats, and in the next with clover, whereby very good 

 yields of oats and clover are obtained, and the ponds are simultaneously considerably 

 in^jroved. After the "summering" the ponds are first used for brood nursery ponds. In 



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