CHAPTER IV 



TILLAGE AND THE MOVEMENTS OF SOIL WATER s 



Water required for the Growth of Crops — The Effect of Drainage 

 — Effects of Autumn and Spring Cultivation, Hoeing and 

 Mulching, Rolling, upon the Water Content of the Soil — 

 The Drying Effect of Crops — Bare Fallows — Effect of Dung 

 on the Retention of Water by the Soil. 



The amount of water transpired by various plants 

 during their growth has been investigated by Lawes 

 and Gilbert at Rothamsted, by Hellriegel in Germany, 

 and Wollny in Munich, and by King in America. The 

 general principle upon which these observers have 

 worked, has been to grow the plants in pots and 

 measure the amount of water consumed during growth, 

 care being taken to eliminate or allow for losses by 

 evaporation from the bare ground, and also to render 

 the conditions of the plant's life as similar to those of 

 the open field as possible. Finally, the plant is washed 

 free of soil, dried, and weighed, so that a ratio is 

 obtained between the dry matter produced and the 

 water consumed during growth. 



Some of the numbers obtained are given in the table 

 below : it will be seen that the same plant gives very 

 different results with the different observers. 



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