phosphate containing about 25 percent citrate soluble, dlcalcium phosphate with about 35 

 percent citrate soluble plus 2 percent citric acid soluble, and Thomas meal with about 

 13 to 20 percent citric acid soluble phosphoric acid. The phosphoric acid In Thomas 

 meal is the most difficult soluble, however Thomas meal contains about ID to 50 percent 

 of calcium oxide. It is therefore especially suitable for acid and for light pond 

 bottoms. Super-phosphate with the most easily soluble phosphoric acid is especially 

 suitable for heavy bottoms. Cicalcium phosphate contains about 28 percent of active 

 lime, Rhenania phosphate about li^ percent calcium oxide, both are intermediate in action 

 between super-phosphate and Thomas meal. 



Bone meal and other fertilizers are naturally suitable also. Bone meal of course, 

 acted less favorably than other phosphoric acid fertilizers in Wielenboch. The local 

 price of the fertilizers is frequently the most decisive for the choice of one or another 

 fertilizer. 



In Wielenbach, according to Walter, the best results are obtained with 25 to 30 kilo- 

 grams of pure phosphoric acid per hectare (22 l/it to 26.7 pounds per acre), in Cma Mlaka, 

 according to Roessler, with 3 dozen per hectare (267 pounds per acre) of super-phosphate. 

 In agriculture similar amounts are distributed and in pond culture practice, I have r»- 

 peatedly been able to determine that favorable results were obtained with about 2 dozen 

 per hectare (178 pounds per acre) of super-phosphate or Thomas meal. Also according to 

 Nolte, about 30 kilograms P2O5 per hectare (26.7 pounds per acre) proved best In the 

 most variable conditions. 



With that sort of a fertilization increased yields were attained in Wielenbach of 

 30 to 100 kilograms per hectare (26.7 to 89 pounds per acre, about 50 to 100 percent, and 

 in Cma Mlaka of 50 to 125 percent. In the last years the effects in Wielenbach were to 

 a large extent weaker than formerly. According to Demoll, the spring weather is very 

 decisive for the phosphate effect. Nolte calculated from 12 fertilization exjjeriments 

 (which however were clouded by many kinds of unfortunate accidents) performed in practical 

 managements, an average increased growth of only 16. A kilograms per hectare (14.6 pounds 

 per acre). Even then phosphoric acid fertilization still has economical advantages, be- 

 cause 1 kilogram of P2O5 produced on the average 0.5A kilogram of fish flesh. 



The after-effects of phosphorus fertilization in Wielenbach in the first year after 

 the fertilization amounted to 7 to 100 psercent, in the second year to 50 percent. In 

 other localities after-effects up to 170 percent were achieved in the first year. In 

 Sachsenhausen the results with phosphate are less clear, since other specially funda- 

 mental and important theoretical problems were worked out there, and the preliminary con- 

 ditions for a full effect were also manifestly unfavorable. 



The indicated amounts of phosphoric acid to be given are to be regarded as "normal" 

 and in like measure as "LEAST-VALURS" . With weaker fertilization, the results as a rule 

 are non-relatively much poorer. Stronger doses (50 to 70 kilograms of P2O5 per hectare, 

 i*if5 to 62.3 pounds per acre) can of course, still further increase the yields, but the 

 increase is not in any economic ratio to the greater application of fertilizer. 



Through- flowing trout ponds, according to experiments by Walter in the years 1924. 

 and 1925, with phosphate fertilization, likewise give increased yields of 50 to 100 per- 

 cent. With the use of easily soluble super-phosphate, the through current must remain 

 shut off approxijnately five days until the fertilizer is absorbed by the soil. 



Fertilization with potash in Wielenbach like in Sachsenhausen and in many other 

 "average to good" ponds achieved no substantial yield increases. Jaemefeld determined 

 that potash at first retards production, increases later with peat mud, but is not per- 

 ceptibly effective with rotted mud. In ponds which are poor in potash there are 

 certainly very different conditions on hand than there are in potash rich ponds, as these 

 experiments of Jaemefeld also show. With a low A.C.V. (acid combining value), potash 

 will react as a detoxicator in liming by counterpoising a one-sided introduction of 

 calcium-ions. A good effect from potash is likewise to be expected in plant-poor hard- 

 soil ponds. According to observations of Uehring, horsetail (Equisetum) is said to 

 disappear after the application of potash and is replaced by soft undeivwater flora. 



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