SOILS AND MANURES 351 



seem able to stand cropping with maize for more than three CHAP, 

 years, but in most cases the abandonment of the land at the VI11 - 

 third year means giving it up just when it should be pro- 

 ducing the very best crops. At Vereeniging an average of 

 18 muids per English acre has been obtained over a field of 

 32 acres, without manure, on steam-ploughed land ; this was 

 the sixth crop of maize from the land, five having been in 

 succession. On new lands the Vereeniging crop has been as 

 low as 2\ muids per acre. 



307. Effect of Tillage. — "Tillage is manure" is an oft- 

 quoted saying attributed to Jethro Tull, but sometimes mis- 

 understood. Prof. Morrow states that proper tillage of the 

 soil increases its productive power ; the ability of a soil to 

 produce crops is often as directly increased by tillage as by the 

 application of manures {Morrow and Hunt, 1). 



Tillage is described by Jethro Tull (1) as "breaking and 

 dividing the ground by spade, plough, hoe, or other instru- 

 ments which divide by a sort of altition (or contusion), as dung 

 does by fermentation. . . . Tillage (as well as dung) is bene- 

 ficial to all sorts of land. . . . The finer the land is made by 

 tillage, the richer will it become, and the more plants it will 

 maintain." But it should not be concluded from this that 

 good tillage makes it unnecessary to manure, for manure 

 adds to the soil, while tillage only makes available what 

 is already there. For a few years after the first breaking of 

 the veld, land may continue to improve and yield better crops, 

 under good tillage, but after that, deterioration begins. 



The following are the principal reasons why cultivation 

 makes soils more productive : — 



(1) Stirring and pulverizing a hard, compact soil enables 

 the roots of plants to penetrate more easily and reach a larger 

 quantity of the salts which are to be converted into plant-food. 



(2) It opens the soil to the weathering effect of air and 

 water, which increases the supply of available plant-food. 



(3) With very fine, loose soils tillage (and rolling) may 

 make them more compact, increasing the capillary action. 



(4) Surface cultivation, which keeps the surface soil loose 

 and dry, forms a mulch, which checks evaporation. 



(5) Tillage kills weeds, which otherwise rob the soil of 

 food and water. 



