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thas under favourable circumstances they are not propagated in such 

 numbers as to prove destructive. From the above it can readily be 

 seen how cultivation tends to maintain the conditions for rapid nitri- 

 fication. 



Many beneficial effects of cultivation can now be easily explained. 

 "We cultivate shallow because such a process not only prevents destruc- 

 tion of roots of the plants, an evil always to be avoided, but also because 

 nitrification takes place in the upper layers of the soil, and by the act 

 of cultivation the ferment is well scattered. Again, the temperature 

 at which fermentation is most active is about 90 degrees to 100 degrees, 

 and this temperature obtains in the upper layers of the soil. The 

 action of the ferment is suspended at or about 50 degrees on the one 

 hand, and 150 degrees on the other. It is destroyed by high heat and 

 electricity ; hence, when lightning strikes a soil, nothing will grow 

 where it struck for some time afterward. The presence in small quan- 

 tities, of lime, highly favours nitrification. Moisture in excessive 

 quantities excludes the air and suspends the vital activities of the fer- 

 ment; hence the necessity of drainage. The absence of moisture is 

 equally as objectionable, and here the second object of cultivation pro- 

 motes the first. 



From these considerations it will be seen that frequent cultivations, 

 provided no roots are cut, are favourable to rapid nitrification. Soils 

 cultivated daily produce better than the same soils cultivated weekly, 

 and the latter better than those cultivated less frequently. (^) 



Besides the beneficial effects of rapid nitrification, other chemical 

 changes of great practical value are induced by shallow and frequent 

 cultivation. The soil is a great laboratory, and the chemical changes 

 taking place there are complex and continuous, and frequent stirrings 

 accelerate these changes and give increased available plant food. One 

 practice must be emphasized here as both wise and expedient, i.e., of 

 breaking the crust after every rain to let in fresh portions of air and to 

 aid nitrification, but under no circumstances should it be done while 

 soil is wet, since this destroys, rather than aids, the ferment. 



The second object in cultivation is to conserve the moisture. On the 

 approach of a drought, cultivators should be run very shallow and 

 almost continuously. In this way the thin layer of earth removed from 

 the great mass of soil is laid as a mulch on the surface, and the con- 

 tinuous upward movement of the water through the soil into the air, 

 is checked just below the surface, and the roots of the plants can then 

 appropriate it. The continuity of capillary pores is broken, and the 

 water therefore passing into the air is arrested just below the surface, 

 and is conserved for the use of the plant. Hence, cultivate continuously 

 in dry weather. One other point : finely divided soils have the power 

 (varying according to character froaa 15 to 23 per cent.) of absorbing 

 iygroscopic moisture from the air, a not insignificant property in a 



(2.) Hence the constant weeding with the hoe, as carried out so largely in the 

 "West Indies, exercises bervoficial results beyond the mere remoral of weeds. The 

 surface soil being gently stirred, nitrification is accelerated, and at the same time 

 cmoisture is conserved by the loosened conditions of the surface goil. — F. W. 



