29 



to be on an average recovered in the crop for 1001b. applied to the land. 

 He also quotes field experiments by J. Kuhn in which 24 per cent, of 

 the nitrogen of farmyard manure was recovered in the crop. Yet in the 

 experiments on the action of dung and farmyard manure, which he pro- 

 ceeds to describe, the fresh dung in every case but one yields a crop be- 

 low that given by the unmanured soil, while farmyard manure gives an 

 average return of only 5 per cent, of its nitrogen in the produce. The 

 conditions of the experiments were thus clearly not such as to allow 

 these manures to be employed to advantage, and the results obtained 

 cannot be taken as indicating what may be expected to happen in the 

 ordinary use of farmyard manure in the field, (i) 



The results obtained by Wagner have naturally excited attention in 

 France, and experiments on the subject, also conducted in pots, have 

 been made by Pagnoul at the Experiment Station of Pas de Calais 

 (1895). His pots were large, containing 25,000 grams of soil, and the 

 quantity of horse dung employed was 500 grams, or 2 per cent. One 

 set of pots remained six weeks without seed and was then sown with 



1 In Maercker's later experiments, just published, much better results 

 were obtained from the use of farmyard manure in pot cultures. 



He experimented with 45 kinds of manure, the history and composition 

 -of which we are fully given. Applied at the rate of one gram of nitrogen per 

 6,000 grams of soil, which, omitting the sheep manures, was equivalent to 17-61 

 ons of manure per acre, he obtained from 38 samples the following results: — 



4 decreased the yieid of nitrogen in the crop. 



7 yielded in increase less than 5 per cent of their nitrogen. 



8 44 " " 5-10 per cent of their nitrogen. 

 7 44 ki " 10-15 



7 " " « 15-20 44 14 



5 44 41 44 over 20 44 " 



In the last group, one manure yielded 37'4 per cent, its nitrogen in the 

 increased crop which it produced. A.s a rule, the most nitrogenous manures, 

 of which consequently, the smallest weight was applied, gave the best return. 



When Maercker nsed smaller quantities than before ot farmyard marure and 

 straw, with nitrate, the depressing effect of the farmyard manure practically 

 disappeared, but that of the straw, was still very marked. The return of ni- 

 trogen in the crop for 190 applied as nitrate of sodium was — 



Nitrate alone 66*6 Nitrate with horse dung 57*2 



" with cow manure 66 44 44 oat straw 23*0 

 14 " sheep manure 62*7 44 44 wheat straw 21.8 



The farmyard manure was used at the rate of 3*3 per cent, of the soil or 33 

 tons per acre. The straw was half this weight, but nevertheless supplied the 

 ■oil with considerably more organic matter than the farmyard manure. 



These new results appear to be in accordance with the views we have ex- 

 pressed above. Maercker does not relinquish in the least his belief in the 

 preponderating influence of the organisms present upon the results obtained j 

 when any specimen of farmyard manure gives results better or worse than its 

 analyses would indicate, he at once assumes that this is due to the absence or 

 abundance of the denitrifying organism. 



