14 



But the function of lime which concerns us most is that of 

 neutraUzing the acids which appear in many soils that have 

 been long under cultivation, and which render the soil in- 

 hospitable to clover. 



An erroneous idea has sometimes been entertained respecting 

 soil acidity. People talk of "souring" the land by turning 

 under a green crop, but the acid developed by this treatment 

 would be carbon dioxide, or carbonic acid, a gas any excess of 

 which would very soon escape from the soil. The acid which 

 causes the soil to redden blue litmus paper and causes clover to 

 fail to grow is not an evanescent gas. The work of the micro- 

 organisms which convert the organic matter of the soil humus 

 into nitric acid would give a plausible explanation of soil 

 acidity, for unless the nitric acid formed by these organisms is 

 removed or neutralized it must eventually accumulate to such 

 an extent as to become toxic to the organisms producing it. If 

 there is an abundance of lime in the soil this acid will combine 

 with the lime, forming nitrate of lime, a neutral salt. 



Indirectly, therefore, lime increases and conserves the nitro- 

 gen supply by encouraging the growth of clover and other 

 nitrogen-gathering crops, and by forwarding the processes by 

 which the organic nitrogen of the soil is made available. 



Returning to the fertilization of truck crops, while the same 

 fundamental principles apply to all crops, yet it may sometimes 

 be justifiable to neglect some of these principles. For example, 

 a crop may have such a high acre-value, and land suited to its 

 cultivation may be so limited, that as a business proposition it 

 may be more profitable to purchase all the nitrogen required 

 for its production than to attempt to secure the nitrogen 

 through the growing of leguminous crops. 



Take the onion, for example. A crop of 1,000 bushels would 

 contain 100 pounds of nitrogen, and a crop of clover that would 

 make 2^ tons of hay would furnish this quantity of nitrogen in 

 its tops, and half as much more in its stubble and roots; but 

 there may be conditions under which the rental value of land 

 that would produce such a yield of onions would be so high 

 that it would be better business to buy the nitrogen outright 

 than to hire the clover to steal it. 



This point is forcibly illustrated in the culture of vegetables 



