March, 1912.] 



239 



Scientific Agriculture. 



On Agdell field the wheat is grown in 

 a rotation — fallow, wheat, roots, barley — 

 wheat being sown only once in four 

 years, On Hoos field the course is fallow, 

 wheat, the wheat coining every alternate 

 year; on Broadbalk wheat is grown 

 every year. No manure is added to any 

 of these three plots, and in particular 

 plot on Agdell field under consideration 

 no clover is grown. Yet the differences 

 in yield are striking ; the wheat grown in 

 rotation without manure is not only 

 greater in yield than the unmanured 

 wheat grown continuously, but it even 

 exceeds the crop on the Broadbalk 

 plot that receives annually a complete 

 dressing of artificial manure including 

 43 lb. of nitrogen per acre. 



It is difficult to account for these ex- 

 traordinary results. Whitney argues 

 from his hypotheses that rotation takes 

 the place of fertilisers, and these figures 

 at first sight lend some colour to his 

 view. But the statistics for the turnip 

 crop put a wholly different complexion 

 on the matter. On the Agdell unmanured 

 plot turnips give a miserably poor crop 

 of less than a ton to the acre, against 

 twelve tons or more on the manured 

 plot ; here then there is no evidence of 

 rotation acting like a fertiliser. It is 

 difficult to believe that the small ex- 

 cretion given off by so insignificant a 

 crop as one ton of turnips per acre could 

 after four years be sufficiently potent to 

 keep the next crop down to the same low 

 level. While, therefore, we cannot 

 accept Whitney's hypothesis, we are not 

 yet prepared with another ; the whole 

 matter remains among the many in- 

 teresting problems as yet unsolved pre- 

 sented by Agdell field. 



Conclusion. 



The outstanding differences between 

 Whitney's hypothesis and those more 

 generally accepted may therefore be 

 reduced by three : — 



(1) Whitney supposes all soils to be 

 chemically alike in that all are made up 

 of the same rock material ; consequently 

 the soil solution is the same in all cases. 

 Other chemists, on the other hand, 

 consider that the soil is more complex, 

 containing colloidal decomposition pro- 

 ducts and a solution which not only 

 differs in composition in different soils 

 but also shows local variations in com- 

 position in different parts of the same 

 soil. 



(2) He further supposes that variations 

 in concentration of the soil solution 

 have no effect on the rate of growth of 

 plants, and that in consequence all soils 

 are equally rich in plant food ; added 

 fertilisers owe their value to other than 

 nutritive effects. 



(3) He considers that infertility must 

 therefore be due to other causes than 

 lack of nutritive compounds ; dismissing 

 considerations of nutrition altogether, 

 he supposes instead that infertility 

 arises from the presence of toxic organic 

 compounds, some of which at any rate 

 may be plant excretions, We, on the 

 other hand, attach great importance to 

 the nutritive functions of the soil con- 

 stituents and of added fertilisers ; while 

 some of us agree that part of the in- 

 fertility of " sour " soils may be due to 

 toxic substances (and apparently the 

 soils examined by Whitney and his 

 colleagues were "sour" soils), we cannot 

 accept the view that plants excrete toxic 

 substances. 



There is no doubt that the work of the 

 Soil Bureau has suffered from leaving 

 out of consideration all biological 

 changes going on in the soil. The de- 

 composition by micro-organisms of the 

 residues of previous fcenerations of 

 plants gives rise beyond doubt to quant- 

 ities of plant food, yet the function 

 of this nutrient material is never 

 considered ; instead attention is con- 

 centrated on possible toxic substances 

 to the exclusion of useful substances. 

 Thus the field of view is unduly 

 restricted. 



The investigations have, however, 

 served a very useful purpose in stimulat- 

 ing inquiry, and Lhey have brought home 

 the fact that the relationships between 

 soils and plants are complex. It is no 

 longer possible to take the old narrow 

 view that the soil simply supplies food 

 to the plant; the earlier papers com- 

 pelled recognition of the fact that the 

 size of the soil particles which regulate 

 the water and air supply is more im- 

 portant than their chemical composition, 

 and consequently that mechanical 

 analysis is more useful than chemical 

 analysis in characterising soils ; the 

 later papers direct attention to possible 

 toxins of which we may have some in our 

 own " sour " soils. We can find much to 

 criticise in the details of the experiments 

 and still more in the conclusions drawn 

 from them ; not infrequently the facts 

 themselves are in dispute. Above all 

 we should like to see a re-examination of 

 the fundamental positions based on 

 definite crucial experiments and con- 

 sideration of alternative hypotheses, 

 But, whether further work support their 

 hypotheses or not, Whitney, Cameron, 

 Schreiner and their colleagues have 

 made agricultural chemists re-examiue 

 their ideas on the soil, and such a recon- 

 sideration must in the end advance the 

 subject, however troublesome or super* 

 fLuous it may at the time appear, 



