11 



-completed in eight Hays. In a third series of experiments Wagner 

 found that in a mixture of garden soil, water, and nitrate of soda the 

 proeesss of denitrification was not quite completed even after 400 days, 

 whereas it was completed in six days when chopped straw had been in- 

 corporated with the mixture. Wagner obtained strictly confirmatory 

 results when he tested the action of straw on the growth of mustard. 

 With nitrate of soda only the yield of dry material amounted to 100.2 

 grammes and contained 2.4'.'5 grammes of nitrogen whereas the addition 

 of a small quantity of straw — equal to less than 1 per cent, of the soil — 

 reduced the yield to 71.5 grammes, and the nitrogen contents to 1.773 

 grammes. 



Can the Denitrifying Action of Dung be Prevented. 



If we accept the results indicated above as proving that farmyard 

 manure has powerful denitrif\ ing properties and it would appear to be 

 impossible to escape from such a conclusion the question comes to bo. 

 What can be done to mitigate the nitrate-destroying action of the dung ? 

 Both Maercker and Wagner found that the denitrifying ferments dis- 

 appear to some extent with age, as the following experiments will show. 

 Maercker prepared a series of pots which he filled with soil, and to all of 

 which he added fresh horse-dung holding 2 grammes of nitrogen. In 

 one ccise he applie nitrate of soda (holding 1 gramme of nitrogen) 

 along with the dung, in another case the nitrate was withheld for four- 

 teen days, while in another case it was not applied tor twenty-eight days. 

 In each case mustard seed was sown at the time the nitrate was applied. 

 When the nitrate was applied along with the dung, the dung reduced 

 the vield (as compared with that got by nitrate only) by 38.8 per cent.; 

 when the nitrate was not applied till fourteen days after the dung, the 

 reduction in the yield which the dung induced amounted to 52.4 per cent; 

 while in the case of the latest application — namely, twenty -eight days 

 after the dung — the crop wis reduced by 54.4 per cent. Evidently, 

 therefore, tour weeks had done nothing to modify the denitrifying pro- 

 perties of the dung — and, in fact, it proved more powerfully denitrifying 

 after lying in the soil for fourteen and twenty-eight days than it was to 

 start with. 



Directly after the first crop of mustard had been reaped a fresh 

 supply of seed ^vas sown on all the pots, and simultaneously one gramme 

 of nitrogen in the form of nitrate of soda was applied. The result with 

 this second crop was that the dung iu one case reduced the yield by 8.2 

 percent., and in another case by 5.7 per cent., while in the third case 

 the combination of nitrate and dung produced a yield that was 7.1 per 

 cent, higher than that grown by nitrate of soda alone. 



When this second crop had been cleared off, seed for a third was 

 sown (the respective dates of the three sowings being separated by in- 

 tervals of about five weeks), another gramme of nitrogen in the torm of 

 nitrate of soda being simultaneously applied. Neither in the case of the 

 second nor of the third crop was any dung applied. The results were 

 practically the same as in the case of the second crop, the dung on two 

 occasions reducing the yield by 13.5 and 9.5 per cent, respectively, 

 while in one case it increased the yield to the extent of 2.2 per cent. 



