96 TILLAGE— MOVEMENTS OF SOIL WATER [chap. 



ploughed field both hinders the flow of the water and 

 affords it many openings by which to sink in ; at the 

 same time the increase of pore space in the loose 

 ploughed layer enables this portion to absorb more 

 water before percolation begins. King has observed in 

 May a difference of 2-3 per cent, of water in the top 3 

 feet of soil between land ploughed in the autumn and 

 the adjoining land not ploughed ; the gain in this case 

 due to the ploughing was no tons of water per acre or 

 rather more than 1 inch of rain. 



The following table shows the effect of ploughing up 

 a stubble in autumn on a thin chalky loam at Wye, 

 Kent, where the soil is only about 2 feet deep. The 

 samples were taken on 3rd March 1902 ; there had 

 been but little rainfall except in the previous December. 

 The figures show mean percentages of water in the wet 

 soil exclusive of stones. 



Of course the autumn ploughing has many other 

 beneficial effects in addition to the above-mentioned 

 gain of water ; the ploughed soil gets alternately frozen 

 and thawed, wetted and dried, with the result that on the 

 stiff lands the puddling effects of trampling, etc., are 

 obliterated, and the soil acquires a loose, open texture, 

 out of which a seed bed can be made. Again, the 

 additional surface which is exposed to the action of frost 

 and rain causes increased weathering, and some of the 

 dormant mineral plant food is brought into a more 

 available condition. 



