VIII.] SANDY SOILS 163 



growth, it is very dependent on a manuring of 

 phosphates, potash being less necessary, because it is 

 fairly abundant on any but the lightest soils. Swede 

 turnips afford another illustration : they are sown late, 

 when spring is well advanced, and after a very extensive 

 working of the soil ; during growth there is also a good 

 deal of intertillage, which promotes bacterial activity, 

 with the result that the crop requires very little nitrogen 

 in its manure though it takes away two or three times as 

 much as the wheat crop does. But with its shallow root 

 system the swede crop is greatly in need of phosphates, 

 and also of potash — perhaps more freqnently than is 

 suspected. The specific requirements of crops will be 

 dealt with more particularly in a later chapter ; but soils 

 show certain real differences, partly chemical and partly 

 physical, which affect their manuring and management 

 and may be now considered. 



Sandy soils are made up, as we have said before, of 

 the coarser grades of particles, and contain as a rule but 

 a small proportion of clay ; it follows that they are easily 

 and rapidly permeable by water, and as they do not 

 retain much water they warm up quickly in the spring 

 and are early soils. Possessing but little clay, they not 

 only dry quickly, but they can be worked when wet 

 without any danger of destroying their texture ; this, 

 again, helps towards early cropping. Their coarseness 

 of grain, however, prevents them from lifting subsoil 

 water readily to the surface, so that crops on them 

 suffer from even short periods of drought, and it is 

 necessary to keep them as consolidated as possible by 

 folding with sheep, rolling, etc., in order to help the 

 capillary uplift of water. Being so warm and well 

 aerated, all bacterial actions go on rapidly in light soils, 

 and humus and other organic materials decay quickly : 

 such soils, therefore, are not retentive of manure but 



