THE MAIN TYPES OF SOIL 53 



green manuring, as a practical agricultural 

 operation, is, on the whole, not common. 



The stock of humus in soil is also increased, 

 often to a large extent, by laying down land 

 to grass, either for a number of years or 

 permanently. The turf that forms is entirely 

 composed of vegetable matter, and should such 

 land again be broken up, the stock of humus 

 will be found to have materially increased. 



Many of the more important market- 

 gardening districts of England are situated 

 upon sandy soil, and no system of agriculture 

 I is more intensive than market gardening. 

 One of the best known market - gardening 

 centres in England is on the Lower Greensand 

 in the neighbourhood of Biggleswade, Potton, 

 and Sandy, in the county of Bedford. There 

 it is not unusual for three crops to be taken 

 off the same area of ground in a single season, 

 and such a result is only possible where land 

 can be worked under practically all conditions 

 of weather, so that no delay is experienced 

 between the removal of one crop and the 

 sowing or planting of its successor. Directly 

 rain ceases to fall one may proceed to plough, 

 cultivate, or sow sandy land, whereas, in the 

 case of clays a considerable interval must 

 elapse after rain before one can venture 

 to tread the soil, or to work it by means of 



