THE PHOSPHORUS GROUP OF FERTILIZERS 29 



to other constituents than the phosphorus is not really known. 

 With a slow-acting fertilizer of this nature, which is a power- 

 ful root stimulant, a very considerable portion of the observed 

 benefits may be quite secondary in their origin. The extra- 

 ordinary change in the physical condition of a soil to which 

 basic slag has been regularly applied must be seen before 

 it can be believed, much less realized and appreciated. At 

 Cockle Park, where this manure has been applied for many 

 years on pasture, the final improvement of the soil has not 

 yet been reached. Between 1897 and 191 6 the result on 

 the physical condition of the soil is shown by comparing a 

 plot that has had no manure with a plot which has basic slag 

 at intervals of about once in four years. The plot that has 

 received no basic slag showed, on careful examination, in 

 1916, no appreciable true soil at all. There was practically 

 sub-soil up to the surface. On the other hand, the plot which 

 had received frequent applications of basic slag now has 

 ten or twelve inches depth of a good loam, and is apparently 

 still increasing in depth, at probably a rate of about half 

 an inch per annum. Such a profound change from a clay 

 to a fibrous loam would of course explain any result, and it 

 is, therefore, quite impossible to attempt to distinguish 

 between the direct results of the addition of so much 

 phosphorus and the indirect results which have benefited 

 the plant by roundabout processes, which have certainly all 

 originated in the application of the slag. As lime, by itself, 

 has, on other plots, achieved but little result, one can only, 

 conclude that the phosphorus is the ultimate origin of the 

 observed fertility. Basic slag must be regarded as one of the 

 more lasting manures, but it appears to become exhausted 

 in time, and, generally speaking, an application once in 

 four years will be necessary. The soils most suited are 

 undoubtedly heavy clays and soils of a peaty character, 

 whilst a sandy soil does not show such satisfactory results, 

 unless it is manured at the same time with one of the 

 potassium group of fertilizers (see p. 40). Basic slag has 

 even been used with great success on very poor pastures 

 on chalk, and seems to be one of the most generally useful 



