96 ON THE TIME OF APPLYING MANURES. 



quite clear that no important benefit can be produced by it. 

 Its effect in this case will be determined neither by the quan- 

 tity of the substance we apply, nor by the quantity of it already 

 contained in the soil, but by the absence of other substances 

 which are necessary to its usual and legitimate action as 

 mortar is necessary to the builder, to render available the 

 bricks and stones already at his disposal. 



7. General suggestions for experiments on the most profitable 

 time of applying different saline and other substances when 

 employed alone. 



I have already drawn the attention of my reader to the in- 

 fluence which the application of a substance at one period of a 

 plant's growth, or at one period of the year, may have upon 

 its sensible effect in promoting or retarding vegetation. 



Chemical physiology and agricultural experience, so far as 

 they have gone, appear to indicate that in our climate 



1. There is, in regard to many of those substances which 

 we do or may profitably apply to our crops, a certain period of 

 the year, or of the plant's growth, at which, other things being 

 favourable, each substance may be most advantageously and 

 economically applied to each crop on each soil. 



2. That smaller applications of a given substance at suc- 

 cessive periods of growth may be more profitable than one 

 larger application made at once. 



But we have as yet little certainty in reference to these 

 points ; and I may say no accurate experimental results which 

 are beyond impeachment. I would suggest, therefore, that 

 series of comparative experiments with each or any of those 

 saline substances, of which I shall speak in the following pages, 

 should be made at different periods and in different successive 

 portions, as follows : 



1. At different periods the whole applied at once. 



a In autumn, or early winter, when the manure is ploughed 

 in or the seed sown. 



The experience of some of the Yorkshire fanners, who apply 

 rape-dust largely to their wheats, is, that the effect is much the 

 same, whether it be harrowed in with the seed in autumn, or 



