02 Cultivation cmd tillage 



that shields from the wmd not only protects the crop 

 but also keeps the soil moist : a road with high hedges 

 at each side remains wet for a long time after more 

 exposed parts have dried. The effect on the tempera- 

 ture can be well seen on a day when a KE. wind is 

 blowing. Fix up on a piece of the experimental ground 

 a little hedge made of small pea-stakes or brushwood, 

 and take the soil temperature at one inch depth, both 

 on the windward and on the leeward side. Two results 

 were : — 



Temperate at 1 inch depth — sheltered side 15°-5 

 „ „ „ windward side 14° 



We have already seen that on the hot day, June 20th, 

 the top half-inch of soil was hotter than the air: the 

 mercury in the thermometer rose directly it was put 

 into the soil. There is nothing very unusual about this ; 

 if you touch a piece of iron lying on the soil you find it 

 hotter than the air. Lower down the soil had the same 

 temperature as the air, and still lower it was cooler^. 

 The sun's heat travels so slowly into the soil in summer 

 that months pass before it gets far down, but then, as it 

 takes so long to get in, it also takes a long time to get 

 out, and it takes still longer to get either in or out if 

 there is a mulch or if grass is growing. 



During the early winter you may notice that the 

 first fall of snow soon melts on the arable land but 

 remains longer on the grass ; towards the end of the 

 winter, however, the reverse happens and the snow 

 melts first on the grass. There is no difficulty in ex- 

 plaining this. The arable land is, as we have seen, 

 warmer in autumn and early winter than grass land, 



^ At great depths below the surface the temperature rises again from 

 quite another cause. 



