342 WHEN THE USE OF NITRATES IS BENEFICIAL. 



of the Weald in Sussex (Mr. Dewdney), and on the Oxford clay in 

 Berkshire (Mr. Pusey), the use of the nitrate has heen attended with 

 general benefit upon oats and wheat, while on the plastic clay in Sur- 

 rey (Mr. Barclay), it has been uniformly unsuccessful. The cause of 

 these differences is to be sought for, most probably, in the chemical con- 

 stitution of the several clays, which are known to be very unlike. The 

 "Weald clay is a fresh- water formation, contains much fine grained 

 siliceous matter (page 244), and is, therefore, comparatively per- 

 vious to water. The Oxford clay soils in Berkshire abound in lime, 

 and must, therefore, be in some degree pervious, while the plastic clay 

 of Surrey, where they are stiffest, contain little lime and partake more 

 of the impervious character of pipe clays. It may possibly be in such 

 differences as these that we are to find an explanation of the discordant 

 results of different experimenters, but much further observation is still 

 wanting before we can si)eak with any degree of confidence upon the 

 subject. 



To some an explanation may appear to be most easily given by sup- 

 posing the one soil to have been rich in soda, while the other was de- 

 fective in this substance. I shall advert to this point in explaining the 

 theory of the action of the nitrates of potash and soda. 



g. Circumstances in which the employment of the nitrates is most hene- 

 Hcial. — 1°. It appears to succeed most invariably in lands which are 

 poor — or out of condition— or on which the corn is thin. Every farmer 

 knows that the most critical time with his crop, as wdth his cattle, is 

 during the earliest stage of its growtli. If it come away quickly and 

 strong during the first few weeks, his hopes are justly high, but if it 

 droop and linger after it is above the ground, his fears are as justly ex- 

 cited. It is in this latter condition of things that an addition of nitrate 

 comes to the aid of the feeble plant, re-animating the pining shoots, and 

 making the thin corn tiller. On rich lands and thickly growing crops it 

 only causes an over-growth of already abundant straw. According to 

 the experiments of Mr. Barclay, it is most advantageous when sown 

 Droad-cast.* 



2°. Whatever may be the chemical nature of the surface soil, the 

 success of the nitrate seems to be most sure where the land is not wholly 

 destitute of water, where the soil is open enough to allow it readily to 

 descend, and yet the subsoil sufficiently retentive to prevent it from 

 being readily waslied away. 



3°. I throw it out as a suggestion which has occurred to me from a 

 comparison of the results contained in tlie above tables, with the kind 

 of soils on which the experiments were made — that probably the pre- 

 sence of lime in the soil may tend to insure the success of the nitrate. 

 In many of the instances of large crops obtained by its aid the land was 

 either naturally rich in lime, or it had, in the ordinary course of hus- 

 bandry, been previously marled or limed. 



h. Theory of the action of the iiitrates. — The nitric acid of these salts 



' A valuable precept also is, to proceed cautiously in the use of theso expenaive Bub- 

 etances — making small trials at first, and increasing the quantities employed as success 

 may warrant. By this mode of procedure, large lessee, of which I have heard, would 

 have been avoided. 



