8 



156.0 to 62.6 grammes and when added to pot* getting cow- 

 urine, the drop wa« from 2L6.7 to 146.1 grammes. Or, from 

 the point of view of nitrogen recovery, the ease may be stated 

 thus : that whereas 77 per cent, of nitrogen was recovered when nitrate 

 of soda was used alone, >>nly 52 per cent, was recovered when in the 

 presence of horse-dung ; the percentage reduction in the case of sulphate 

 of ammonia being from 69 to 50 ; in the case of chopped grass from 43 

 to 20 ; and in the case of urine from 69 to 40. 



What, then, is the cause of the depressing action of dung, especially 

 horse-dung, on more active forms of nitrogen ? It might be urged that 

 the dung in some way or other prevents the organic nitrogen in, say, 

 green manure from being converted into ammonia ; but that this ex- 

 planation is valueless is proved by the fact that the dung also mater- 

 ially interfered with the action of sulphate of ammonia. Nor can it 

 with justice be urged that the depressing action of the dung is due to 

 its interference with the nitrification of ammonia for the loss was quite 

 as great when a ready-formed nitrate was applied to the >o\\. 



When fresh or comparatively fresh dung is applied to a crop, and 

 especially to a cereal crop, it frequently causes the plants to assume a 

 pale yellow, unhealthy colour. This unhealthy condition might be due 

 to one or other of two causes : either the dung might unfavourably affect 

 the physical condition ot the soil ; or, while itself offering no available 

 nitrogen to the plants, it might have an injurious influence on the avail- 

 able nitrogen naturally present in the soil. In the latter case the un- 

 healthy character of the crop would be due to the plants being more or 

 less starved as regards nitrogen, and that this is the true explanation is 

 clearly indicated by Wagner's pot experiments with oats. When the 

 plants were about six inches high it was found that those in the dunged 

 pots were much yellower than those in the unmanured soil, and while in 

 this condition they received a weak solution of nitrate of soda. Doubt- 

 less some of the nitrate was rendered inoperative through contact with 

 the dung, but enough was absorbed by the plants to produce a marked 

 change in colour in three davs, while in a week the sickly yellow colour 

 had entirely disappeared. 



To show that the disappearance of the nitrogen of nitrate of soda in 

 presence of dung is not due to its sinking into the subsoil, and is only partly 

 due to its appropriation by plant-roots, Wagner carried out the following 

 experiment, in which no plants whatever were grown. A number of 

 pots were filled on Jnne 1st, with 3.4 kilogrammes of garden soil, to 

 which had been added 0.66 gramme of phosphoric acid and 0.49 

 gramme of potash in the form of potassium phosphate. Certain of the 

 pots received £ gramme of nitrogen in the form of nitrate of soda ; 

 others received 600 grammes of horse dung, while others received both. 

 Six weeks later, namely on July 10th, the soluble contents of the pots 

 were carefully extracted with water, when it was found that where no 

 dung was used the nitrate of soda was still present to the extent oi 93 

 per cent., whereas in the pots getting horse-dung only 42 per cent, of the 

 nitrate of soda remained. Not only had the dung dissipated a very 

 large quantity of the nitrogen of the nitrate of soda, but it had also acted 

 on the natural nitrates of the soil, and destroyed them as well. This is 



