178 LECTURES ON 



LECTURE IY. 



IMPROVEMENT OF THE SOIL BY TILLAGE, DRAINAGE, AMENDMENTS, AND 



FERTILIZERS. 



Having attempted to define at length the reasons of fertility in the 

 soil, we may appropriately recapitulate this part of our subject in 

 order to set in a clearer light the means of improvement. 



1. A fertile soil must contain all the mineral matters (ash) of the 

 plant. 



2. It must include a certain store of atmospheric ingredients, viz: 

 organic matters or their equivalents — ammonia or nitrates — in short, 

 some store of nitrogen, and usually of carbon. 



3. It must contain these matters in an available or assimilable form, 

 i. c, in a certain degree of solubility in water, thus yielding them to 

 vegetation as rapidly as required. 



4. The soil must be free from noxious substances. 



5. Must possess favorable physical characters, be neither too porous 

 nor compact, neither too wet nor too dry; must afford a congenial 

 home and lodgment for the plant. 



It is comparatively rare that these conditions are perfectly fulfilled 

 in nature, or if they exist in any given place at a certain time they 

 suffer disturbance after a longer or shorter period. Hence the ancient 

 and wide spread art of cultivation or improving the soil. Hence, 

 too, the immense practical importance of a scientific, i. e., accurate 

 and complete understanding of the conditions of fertility and of the 

 means of communicating or restoring them. 



The method of improvement, like the characters of the soil, fall 

 naturally into the two classes, mechanical or physical, and chemical. 



The first class of improvement comprehends tillage, drainage, and 

 mixture. 



In the second class is included whatever contributes to the nourish- 

 ing qualities of the soil, either by direct addition of the food of plants, 

 or of agents that collect, solve, or otherwise prepare this food, as 

 manures and amendments. 



This division, though warranted for convenience of study, has no 

 practical existence, for the chemical and physical phenomena of 

 nature are always so intimately associated that their rigorous sepa- 

 ration is, in most cases, impossible. 



In a very fertile soil it is only needful to deposit the seed in favor- 

 able circumstances as regards temperature and weather, and in due 

 >time the harvest is ready. In such a soil there is a sufficient store 

 ■of plant food, and all the external conditions of rapid vegetable 

 growth. In the poorer soil, in most soils, in fact, there is some want 

 to be. supplied, some improvement to be attempted. The first step 

 in meliorating the soil, the one almost universally indispensable even 

 in fertile soils, as a preparation for the seed and young plant — the 

 step always first made in practice and the one in general first required 

 by •enlightened .theory, is tillage. 



