41 



addition of a dressing of nitrate of sodium is attended with a good return 

 for the additional nitrogen applied ; this fact is shown bv the earlier re- 

 sults when the nitrate was applied before the dung ; it is shown still 

 more in the later experiments, when the nitrate was applied as a top- 

 dressing to the young plants, and when the supply of potash to the crop 

 was at the same time increased. The amount of farmyard manure 

 employed in the Rothamsted field is a moderate quantity, and w r e must 

 not therefore conclude that no deterioration in the action of nitrate of 

 sodium will take place where much larger quantities of dung are made 

 use of. The danger of denitrification reaching considerable proportions 

 will increase as the amount of fermentable organic matter in the soil 

 increases, and will be much aggravated by a wet condition of the land. 

 Tho horticulturist who employs dung in large quantities is mucb more 

 likely to suffer from denitiificatioii than the farmer. 



The mode in which farmyard manure is applied, and the extent to 

 which it is incorporated with the soil, must have some influence upon its 

 action. When farmyard manure is ploughed in. it is not intimately 

 mixed with the whole soil, as in a pot experiment, but is left in a succes- 

 sion of layers separated by unmanured soil. When roots are grown on 

 the ridge system, the farmyard manure is confined to the centre of the 

 ridge. In either case the denitrifying zone is limited in extent, and does 

 not include the whole of the soil penetrated by the roots. There is 

 clearly much scope for careful enquiry as to the most profitable method 

 of employing dung with other manures. 



Wo now turn to the experiments made at Rothamsted with straw. 



During twelve years, 1868-79, the straw of the preceding year's 

 crop was applied to one-half of certain plots in the experimental wheat 

 field. None of these plots received nitrate, but nearly all of them am- 

 monium salts. We will take as our first illustration Plot 7, which re- 

 ceives a complete supply of ash constituents, with 400 lb. per acre of 

 ammonium salts, supplying 86 lb. of nitrogen. 



During sixteen years before the straw was applied the average total 

 produce of the two halves of Plot 7 was, for 7a, 6,339 lb. and for 7b. 

 6,412 lb. per acre per annum, or a difference in favour of 7b, of 73 lb. 

 During the twelve years, 1868-79, the straw of the previous season, 

 amounting on an average to about 3,000 lb. per acre, was cut into chaff, 

 spread on Plot 7a, and ploughed in during October. The other manures, 

 including the ammonium salts, were applied at the same time in ten 

 years out of the twelve; in the other two years the ammonium salts were 

 applied as a top-dressing in the spring. During the twelve years in 

 which strttw was applied the average produce of 7a, was 4,973 lb. and 

 of 7b, 5,185 lb., or a difference in favour of 7b of 212 lb. ; from this we 

 may deduct 73 lb., representing the original superiority of 7b. We 

 have thus an annual loss by the usft of straw amounting to 139 lb per 

 acre, diminishing the produce of Plot 7a by 2.7 per cent. 



On Plots 6 and 8, also receiving a full supply of ash constituents, 

 with 200 lb. and 600 lb. respectively of ammonium salts, the return of 

 the straw, carried out in the same manner as just mentioned, occasioned, 

 in the case of 6a an average diminution of 38 lb. of total produce, and 



