176 THE YEAR-BOOK OF AGRICULTURE. 



cost. The soils of those gentlemen contained rather more potash than usual. But he had 

 yet to find the first soil which is not capable of being benefited by the addition of the super- 

 phosphate of lime. 



Phosphates in Turnips. 



LIEBIG, in his recent work, appends the following note on the amount of phosphates found 

 in turnips. The note occurs in connection with the following sentence, and ; has special 

 reference to some experiments of Messrs. Lawes and Gilbert, of England, which are in oppo- 

 sition to the views of Liebig: 



"The small percentage of phosphates contained in the turnip is the reason why, in Ger- 

 many and France, there is often obtained after grain a stubble crop of this root in the same 

 year." 

 The note is as follows: 



"If we calculate from the results of ash-analyses the quantities of phosphoric acid which 

 are required respectively by a wheat crop, including grain and straw, and by a turnip crop, 

 including roots and leaves, we find that wheat removes less of this substance from the soil 

 than turnips. This result is apparently in contradiction to the fact so well established by 

 practical experience, that wheat requires more abundant supplies of phosphoric acid in the 

 soil than the turnip. The two facts become reconciled when we take into account the longer 

 time that the latter has in which to accumulate this mineral ingredient. 



" The turnip requires phosphoric acid to be supplied through the whole of its long period 

 of growth, four or five months, but uniformly and always in small quantity only in a given 

 time. Wheat needs the greater share of its phosphoric acid during the growth of the seed. 

 This is the period in which, as practical men believe, the soil suffers the greatest is most 

 exhausted. If the wheat-plant finds a sufficient quantity of phosphoric acid within reach of 

 its roots during the few weeks in which its seed is formed, then each kernel attains a full and 

 normal development; if there be a slight deficiency of phosphoric acid, then the seeds are 

 less numerous or less large ; if the deficiency be very considerable, then nothing but straw 

 is produced. 



"The quantity of phosphoric acid which a wheat soil should contain does not therefore 

 stand in relation to the sum total which the plant needs, but to the quantity which the ker- 

 nels require during the period of their development. 



"When we compare the quantity of phosphoric acid which the soil must yield to a wheat 

 crop during the month in which its seeds are forming, with that needed by a turnip-crop in 

 any equal space of time, it is plain that wheat requires the presence of a far larger amount 

 of this indispensable body in the soil than the turnip. This is a fact not to be disregarded 

 in manuring the soil for these crops. 



" The produce of a field stands related to the amount of that mineral ingredient which its 

 soil contains in smallest quantity. 



"As a general rule, the manuring of a field should not be calculated from the sum total 

 of mineral ingredients which the plant takes from the soil, but must be proportioned to 

 that maximum of these substances which is required by the plant in a certain period of its 

 growth." 



In respect to the above, Mr. S. W. Johnson, of England, in a letter published in the 

 Working Farmer, says: 



"The above makes evident how necessary it is that not only the kind and quantity of 

 substances removed by a plant from the soil be considered, but also the time and circum- 

 stances in which the supply should be made. The latter are of equal moment with the 

 former. Plants differ physiologically and structurally. These differences must be investi- 

 gated, and taken into account. The chemist has hitherto too much neglected them. He has 

 attempted in many cases to deduce the whole list of the plant's chemical needs from its 

 chemical analysis. Nothing could be more fallacious. He has found that an average crop 

 of wheat and turnips contain nearly the same amount of phosphoric acid. He cannot, 

 therefore, conclude that, so far as this ingredient is concerned, they will both flourish equally 

 in the same soil." 



