Philip Buckle 141 



(iii) the effect of cultivation. 



In studying the effect of cultivation upon the soil fauna, a com- 

 parison of that of grass and arable land in similar areas will be of 

 value, since it may be taken that grassland is the immediate initial 

 condition and that differences demonstrated on arable land are due to 

 environmental conditions induced by cultural operations. It will be 

 seen from an examination of the hsts of species attached to this paper 

 that such a comparison leads to several definite conclusions. 



(1) The distribution and numbers of the soil fauna are more stable 

 on grass than on arable land. Grassland bears a vegetative covering 

 through a period when little, if any, vegetation exists on arable land. 

 Consequently food material is always present for the large majority of 

 species, since soil fauna are predominantly phytophagous forms. At the 

 same time the land is not cultivated and the hibernation of species or 

 period of lessened activity proceeds normally. On arable land, the 

 opposite is the case, the winter ploughing and working of the soil brings 

 the fauna to the surface and exposes the animal life not only to the harsh 

 climatic conditions but also to bird attack. 



(2) There is a corresponding increase in the fauna on both arable 

 and grassland as vegetative growth increases. This circumstance is to 

 be expected since conditions favourable to plants are those most suited 

 to animal life. That this increase does take place on arable land is shown 

 either by the absence or great scarcity of species from the earlier samples 

 taken in winter. It will be understood that the conditions in winter and 

 early spring are extremely detrimental to soil fauna. At that time all 

 circumstances combine to reduce animal Hfe in a drastic manner on 

 arable soil. 



It may be said that the fauna of arable land consists of (a) Species 

 which have existed from the previous year by passing the winter in the 

 soil; (b) Species which are introduced or migrate there in the growing 

 season. 



With regard to the first class the survey has shown that at a time 

 when the wintering species were alone in occupation few are obtained 

 in the samples. 



The fact that the increase of numbers on arable land always lags 

 behind the increase on grassland, rather indicates that grassland is the 

 source of the influx of fauna on arable land in the growing season. Of 

 course certain species will be attracted to the particular crop and may 

 form the dominant ones for that year. With regard to those commonly 

 occurring it does not seem that their limited numbers on grassland are 



