34 



Wagner mentions, at the commencement of this paper that, tinder 

 the conditions of practical agriculture, 55 per cent, of the nitrogen of 

 nitrate of sodium may be expected to bo recovered in the crop. In the 

 pot experiments we have earlier mentioned the return has varied from 

 55 to 77 per cent. In the Kothamsted field experiments with barley, 

 nearly 60 per cent, of the nitrogen of a moderate dressing of nitrate of 

 sodium has been on an average recovered in the increased produce where 

 a liberal amount of ash constituents has been supplied. Sulphate of 

 ammonium Wagner finds to give on an average one-tenth less return than 

 nitrate of sodium for the same amount of nitrogen applied. Bearing 

 these facts in mind, the percentage of nitrogen recovered in the in- 

 orease of crop by the use of nitrate of sodium and sulphate of ammonium 

 in the mangel experiments appears quite satisfactory. The nitrate of 

 sodium employed as a c ross-dressing is utilised to the extent of 53.6 per 

 cent where 14 tons of farmyard manure are applied, and the utilisation 

 reaches 68.9 per cent, where superphosphate is also employed. With 

 ammonium salts, the utilisation under these two conditions is respec- 

 tively 58.0 and 67.3 per cent. It will be observed that although super- 

 phosphate and farmyard manure give no greater crop of roots than farm 

 yard nanure alone, yet, when nitrate or ammonia is used in addition, the 

 presence of the superphosphate produces a considerably greater increase 

 of crop. The supply of phosphates becomes insufficient only when the 

 supply of nitrogen is increased. We shall see presently that still bette. 

 results were obtained when potash was supplied as well as phosphatesr 

 The, cross-dressing of rape-cake has been utilised to the extent of 47.3 

 and 50.7 per cent, without, and with superphosphate. As the rape-cake 

 itself supplies both phosphates and potash, the effect of additional 

 superphosphate is here little perceived. The very heavy cross- 

 dressing of ammonium salts and rape-cake, supplying 1 84 lb. of nitro- 

 gen per acre, is utilised to the extent of 48.6 and 50.7 per cent, under 

 the conditions already mentioned. 



It may fairly be objected that the return for the nitrogen applied is 

 exaggerated in the statement just made, as, in fact, all the mangel leaves 

 from every plot are returned to the soil. To estimate the influence of 

 this return of the mangel leaves on the results before us we need to 

 know what proportion of the nitrogen in mangel leaves spread on the 

 soil in November may be expected to appear in next year's crop of man- 

 gels. If we assume that one-quarter of the nitrugen in the leaves will 

 reappear in the next year's crop, we shall probably be making a liberal 

 concession to the objection urged. In using this correction we have to 

 deduct from the average amount of nitrogen in the increase bv nitrate of 

 sodium, or other cross-dressing, one-quarter of the average nitrogen in 

 the leaf ; the remainder will then, according to our assumption, repre- 

 sent more nearly the amount of nitrogen derived from the cross-dress- 

 ing. The difference made by this alteration in tho calculation depends 

 on the proportion of leaf to root usual on the different plots ; the 

 alteration in the figures is quite small where nitrate of sodium is the 

 cross-dressing, aud becomes much more considerable where ammonium 

 salts, and especially ammonium salts and rape-cake are applied. 



Nitrogen recovered in increase of mangel crop per 100 applied at 

 cross-dressing on dung, after deducting from the increase one-quarter of 

 tho average nitrogen in the leaves. 



