ii8 



NATURE. 



[September 22, 192 1 



were collected, and even after fifty years on an 

 axcrag'e the artificials had done as well as the 

 farmyard manure. In consequence of this and 

 other experiments many agricultural chemists 

 developed the view that artificial manures were 

 at least as good as farmyard manure for ordinary 

 use on the farm ; but wider knowledge has shown 

 that this is not the case ; it is only a first approxi- 

 mation to say that artificial fertilisers are equally 

 as good as farmyard manure ; we now know that 

 farmyard manure produces effects of the highest 

 importance to the land which no known combina- 

 tion of artificial fertilisers will bring about. 



Examination of the Broadbalk data in the 

 statistical laboratory recently instituted at Rotham- 

 sted under Mr. R. A. Fisher shows that farm- 

 yard manure differs in two ways from artificials 

 — ^the variation in yield from year to year is 

 diminished by the use of farmyard manure, as is 

 also the deterioration in fertility due to continu- 



our plots treated with artificials excepting perhaps 

 those receiving exceptionally high dressings. This 

 is shown on both the wheat and the barley plots, 

 and it is greatest on those plots where one of the 

 essential fertiliser constituents is withheld (Fig. 2). 



There is a third effect, which is very marked in 

 rotations. Farmyard manure appears to have a 

 greater eifect than artificials in increasing the 

 growth of clover. Unfortunately the number of 

 experiments is not very great, but, so far as they 

 go, they show a striking superiority over arti- 

 ficials, and this extends not only to the clover, 

 but also to the succeeding wheat crop. 



The results at Rothamsted are : — 



Manure applied to previous 

 corn crop. 

 Farmyard Manure 

 Artificials only 



Yield of 



clover 



hay. 

 Cwts. per 



acre. 



62 



46 



Yield of succeeding 

 wheat crop. 



Grain. 

 Bushels 

 per "acre. 



45 



37 



straw. 



Cwts. 



per acr.'. 



45-3 

 36-8 



52'56 57'6I 627l 72'8I 82'9I 92'0l 



Fig. 2.— Eflfect of fertilisers on yield of barley. (Horsfield, Rothamsted, 



ous cropping for eighty years. No fewer than 

 fifteen different combinations of fertilisers are 

 tested against farmyard manure, and while some 

 of them come out quite well on an average of 

 twenty-five or fifty years, they fluctuate consider- 

 ably from season to season, and they show mani- 

 fest signs of deterioration as the years pass by. 

 Many farmers prefer a steady yield to a fluc- 

 tuating one, and this, of course, is sound, cautious 

 business. Farmyard manure never does badly 

 even in the worst seasons, but, on the other hand, 

 it does not give record crops even in the best 

 seasons. What we should like would be some- 

 thing possessing the special values of farmyard 

 manure in bad seasons, and of artificials in good 

 ones. 



Further, there is a deterioration of yield on all 



NO. 2708, VOL. 108] 



At present we cannot explain all 

 these remarkable facts. There are 

 several possibilities : — 



(i) Farmyard manure is known to 

 exercise remarkable physical effects 

 on the soil, causing it to become 

 puffed up so that the empty pore 

 spaces increase in size. The air 

 supply to the roots thus becomes 

 better, the water supply is more 

 evenly regulated, the work of the 

 tillage implements is lightened^ and 

 a good tilth is more easily obtained. 

 The difference is well shown by the 

 root crops — swedes, turnips, and 

 particularly mangolds, which are 

 very sensitive to soil conditions, 

 and, being sown late, are liable to 

 suffer from spring and summer 

 droughts. The plots at Rotham- 

 sted receiving farmyard manure con- 

 tain always some 2-5 per cent, more 

 moisture than those receiving no 

 manure or artificials only, and this 

 enables the mangolds to keep grow- 

 ing during a drought which effec- 

 tually checks all plants not receiving- 

 farmyard manure. 



(2) It is possible that there are chemical con- 

 stituents in farmyard manure which are not 

 present in our artificial fertilisers. The old idea 

 that nitrates, potash, and phosphates only are: 

 necessary may be wrong. Recent work by Maze 

 in Paris and by Dr. Winifred Brenchley at 

 Rothamsted show that some of the other elements 

 may also be helpful. In the Rothamsted experi- 

 ments very small quantities of boric acid added 

 to the soil caused distinct increases in crops fully 

 fertilised with artificial manures. We cannot as 

 yet recommend farmers to adopt this kind of 

 manuring with special substances, because it is 

 very easy to overstep limits and do much damage 

 to the crop, for the plant suffers seriously from 

 even slight excess. With fuller knowledge, how- 



02'll I3'l9 



1852-1919.) 



