10 IMPROVEMENT OF SOILS, CONSIDERED 



irrigation without waste of water. By this last mode, a field or garden 

 is arranged into different platforms, which may either be on the same 

 or on different levels. In the former case, the water is let into one 

 platform after another ; or, if there is an abundant supply, into several 

 at the same time ; in the latter case the supply of water is conducted 

 to the highest platform, which is first watered, and the others follow in 

 the order of their elevation. Arrangements of this kind are not so 

 important in British gardens as they are in those of warmer climates ; 

 but still they might in many cases be advantageously introduced with 

 a view to watering summer crops. 



Burning of soils has been resorted to as a means of altering their 

 texture, destroying injurious substances, and changing or forming 

 others which may act as a manure. Burning is useless on siliceous 

 sands containing little or no vegetable matter ; but on all soils contain- 

 ing chalk, lime, or clay, it may be practised with advantage. By 

 burning calcareous or chalky soils, the same effect is produced as if 

 quicklime had been procured and added to the soil ; and by burning 

 clayey soils the same result is obtained as if sand had been procured 

 and mixed with them. The effect of burning clay is totally different 

 from that of burning sand or lime. On sands and gravels burning 

 can have no effect, except that in some cases it renders the particles 

 smaller. Burning lime drives off the carbonic acid and the water, and 

 renders the lime caustic and well adapted for decomposing organic 

 matter; but the lime has no sooner lost its water than it begins to 

 attract it again, and after a certain period will be found in the same 

 state of combination with water and carbonic acid as it was before. 

 Clay, on the other hand, when once the water is driven off by burning, 

 will never regain it, but remains for ever afterwards in a state which, 

 with reference to its mechanical effect on a soil, is exactly the same as 

 that of sand. This is a fact, the great importance of which in the 

 improvement of clayey soils, and indeed of all soils which are of too 

 compact a texture, is not duly appreciated. It is evident that, by 

 means of draining and burning, any clayey soil may have its texture 

 as much improved as can be desired ; and though the expense of this 

 may, in many cases, be too great for application on an extensive scale, 

 yet it may always be adopted in kitchen gardens ; and often over the 

 entire surface of the grounds of small villas. It is indeed only by this 

 kind of improvement that the heavy clayey soils of many of the small 

 villas in the neighbourhood of London can be at all rendered comfortable 

 to walk on after rains in summer, and throughout the. whole of the other 

 seasons, or suitable and agreeable for the cultivation of culinary vege- 

 tables and flowers. Clayey soils often contain iron, and the operation 

 of burning them, by forming an insoluble compound of iron and alumina, 

 lessens the risk of the iron ever becoming noxious to the plants. 

 Burning also destroys the inert vegetable fibre; and thus it at once 

 produces ashes containing vegetable alkali, and supplies the soil with 

 a portion of humus ; without both of which, according to Liebig, no 

 soil can bring plants to maturity. Where a strong clayey soil is 

 covered with a healthy vegetation, as of pasture or wood, it may not 



