3o8 CAUSES OF FERTILITY AND STERILITY [chap. 



limestone, etc.) or quicklime and slaked lime, which 

 promptly become carbonate of lime when incorporated 

 with the soil, are capable of acting as the required base. 

 Other calcium compounds, as superphosphate of lime or 

 sulphate of lime (gypsum), or phosphate of lime in 

 bones, etc., are either acid or neutral, and do not supply 

 the base required to effect the beneficial actions set out 

 above ; they cannot replace lime or chalk in fact, they 

 do not contain any " lime " in the farmer's sense. 

 Unfortunately, it has been too often supposed that the 

 use of artificial manures, such as superphosphate of lime, 

 removed the necessity of a periodical liming of the soil, 

 and some of the neglect into which this all-important 

 operation has fallen may be set down to the unfortunate 

 confusion hanging round the word lime. However, as 

 will have been gathered from a consideration of the 

 effects of sulphate of ammonia in depleting the Woburn 

 soil of carbonate of lime, the use of artificial manures 

 generally demands an increased rather than a lessened 

 attention to the periodical liming of the land. 



The method of liming which was formerly in vogue 

 consisted in applying very large quantities of quicklime 

 at comparatively long intervals, ioo to 150 bushels 

 per acre ( = 2 to 4 tons) every eight or ten years, or 

 an initial dressing of 100 bushels, with a further dressing 

 of 50 bushels per acre every third year. The reason 

 for this interval lies in the fact that the best effects 

 of lime are to be seen after the lapse of a year or 

 two ; the material becomes carbonate, which, being 

 insoluble, is incorporated with the soil and passes into 

 solution as bicarbonate but slowly. The immediate 

 effect of lime may even be a diminution of the crop 

 if it be used on very rich land, or in actual contact with 

 fresh dung ; under these conditions there appears to be 

 some loss of ammonia by volatilisation. Of course the 



