DR. DAUBENY ON THE ROTATION OF CROPS, ETC. 247 



Thus it is seen, that whilst the entire quantity of phosphate present in 100 square 

 feet of the garden soil amounted to 4391 1 grains, or exceeded 6 lbs., and that of alkali 

 (including both potass and soda) to 233,700 grains, exceeding 33 lbs., all that could 

 be extracted from the same quantity of soil by water was, 7134 grains of phosphate, 

 and an amount of alkali sufficient to produce 83,640 grains of sulphate. 



It appears, moreover, that, in the soils which had been drawn upon for ten years, 

 either by the same crop or by a succession of different ones, without the application 

 of manure, whilst the actual amount of phosphate and of alkali was fully as great as 

 in the other parts of the garden, the quantities extracted by water were many times 

 less ; and although it need not be supposed, that what had been withdrawn by two 

 quarts of water constituted the whole amount of these substances which was available 

 at the time for the purposes of vegetation, yet it seems probable, that the facility with 

 which the above ingredients were supplied to the plants, would bear some relation to 

 the quantities taken up by the same amount of water from the different soils. 



Since, therefore, the amount of phosphates and of alkalies extracted by two quarts 

 of water in these cases falls considerably short of the quantities of those ingredients 

 required for an average crop of barley, such as that produced for ten years in succes- 

 sion in the same soil, it may be fairly concluded, that the deficiency in the produce 

 arose in part from a less ready supply of these constituents being provided, than 

 would have been the case in soil newly broken up, or recently manured, where, although 

 the absolute amount of nutritious principles may not be very different, the proportion 

 of them in a state directly applicable to the uses of the plant will be much greater. 



This hypothesis however seems to me only to afford a partial explanation of the 

 problem before us; for repeated instances occur in this paper, of two soils presenting 

 no apparent difference in the condition of their ingredients as to solubility, and in 

 other respects alike, which nevertheless have varied very materially in the amount 

 and quality of their produce, according as the crop has been a permanent or a shifting 

 one ; so that in these instances, the crop had extracted different quantities of phos- 

 phates and of alkalies from two soils, both of which were capable of supplying them 

 with these principles, with equal readiness, and in equal abundance. 



This circumstance might seem to favour the idea, that the quantity and condition 

 of the organic matter present in the soil may exercise some control over the deve- 

 lopment of the crop. 



Upon the whole, then, it must, I think, be admitted, on the one hand, that the 

 quantity of inorganic matter brought into a soluble condition would, other things re- 

 maining the same, be more considerable in proportion to the activity with which the 

 processes of vegetation are carried on, inasmuch as those operations which result 

 from the vitality of the plant, would facilitate that introduction of air and water into 

 the body of the soil, by which a fresh portion of the above ingredients might be 

 brought into a more soluble condition—owing to the separation of the clods of earth, 



