422 Effect of Chalk on Heavy Land. [Aug., 



the compacting of the soil in front of the plough by the Titan 

 tractor, which weighs 60 cwt. against 30 cwt. for the Austin. 

 In addition the Austin runs with two wheels in the furrow, 

 whereas the Titan runs on the unploughed soil. 



It would be interesting to know just why chalk or lime has the 

 remarkable effect here described, and the inquiry is being made 

 in the Soil Physics Laboratory at Eothamsted, because the action 

 cannot properly be exploited until it is understood. 



It is possible that the chalk affects the degree of moistness of 

 the soil. There is a difference in the appearance of the land 

 after rain, which suggests a difference in moisture content. In 

 walking over the field in winter one notices a drier, more porous 

 look on the chalked plots, and the land is less sticky; this is 

 seen every winter, and is frequently demonstrated to visitors. 

 This is no doubt an important factor in determining the improved 

 growth of clover on chalked land, which then reacts on the sub- 

 sequent crops. 



It would not follow that the soil was actually drier because it 

 looked so : the same results would be obtained if the soil were 

 lightened or puffed up so that its pore space were increased. 



It is not proposed, however, to discuss here the reasons for 

 the effect of chalk : the important point is that chalk lightens 

 the soil to the marked extent indicated by these measurements. 



It is hoped to be able to extend these measurements and 

 ascertain the effect of other manures on the work of cultivation. 

 Farmyard manure is known to lighten the soil : green manure 

 is assumed to have the same action. Sir A. D. Hall, when at 

 Bothamsted, showed that the various artificial manures acted on 

 soil each in a characteristic way. and it seems probable that 

 these also m.ay affect the work of the tractor. It is obvious that 

 any action a fertiliser may have in increasing or diminishing 

 the resistance of the soil to the tillage implements must be taken 

 into account by the farmer in determining his choice of materials 

 for use. 



