THE BENEFITS OF TILLAGE 111 



is plowed, harrowed or cultivated it is loosened, 

 and air, water, heat and cold enter it more freely 

 and attack it more vigorously. Nearly all farm 

 soils, even some that produce poor crops, contain 

 enormous quantities of plant food (Chapter XI), 

 most of which, however, is in such a form that the 

 plants cannot use it, being "unavailable" as the 

 chemist says. Tillage makes much of this latent 

 plant food available from year to year, by pro- 

 moting better weathering. 



Tillage mixes the soil grains and changes their 

 relative positions so that certain particles are 

 brought together that have been separated before, 

 and there is greater likelihood of chemical changes. 

 It may carry to the surface grains of soil that have 

 been lying several inches deep for many years, thus 

 exposing them to weathering. It fills the soil with 

 air which hastens the decay of vegetation, thus 

 making humus and a large amount of carbonic 

 acid. This carbonic acid becomes a part of the 

 soil water and greatly increases its power to dis- 

 solve plant food from the mineral portion of the 

 soil. The better aeration of the soil due to tillage 

 is favourable for the growth of the valuable nitro- 

 gen-fixing bacteria described on page 40 . The 

 activities of other beneficial germs in the soil are 

 promoted by the warmth, drainage and aeration 

 that follow tillage. If it were not for these benef- 

 icent effects of tillage soils would become "worn- 

 out" much sooner than they do now from con- 

 tinued cropping with little return. 



Tillage the "Poor Man's Manure"- -Tillage has 

 been called "the poor man's manure," with some 

 fitness. Stirring the soil does enrich it to the ex- 

 tent that it enables the farmer to use more of the 

 native plant food in the soil. But it is not a manure 



