LIME AND OTHER SOIL AMENDMENTS 121 



form. It may combine with certain soil elements liberating other elements 

 such as potash, and making them available for plants. Lime in the pres- 

 ence of soluble phosphates will readily combine with them, forming 

 tricalcium phosphate. This will prevent the phosphates from uniting 

 with iron and aluminum, which gives rise to compounds less available to 

 plants than the lime phosphates. 



Physical Effect of Lime. — Clay soils are frequently improved in 

 physical condition by the liberal application of lime. Freshly burnt lime 

 is the most active form for this purpose. Lime causes a flocculation of 

 the clay particles and increases the porosity of the soil. Lime, therefore, 

 facilitates drainage, makes cultivation easier, causes an aeration of the 

 soil and makes possible a deeper penetration by plant roots. On sandy 

 soils burnt lime may tend to bind the particles together. This may or 

 may not be desirable. When applied for its physical effect it is usually 

 best to apply air-slaked lime or finely pulverized limestone to sandy soils, 

 and to use freshly burnt lime on heavy, refractory soils well supplied with 

 organic matter. 



Lime Affects Soil Bacteria. — Certain species of bacteria are instru- 

 mental in the change of ammonia and inorganic forms of nitrogen to 

 nitrates. This process is known as nitrification, and is promoted by the 

 presence of lime in the soil. The process not only makes the nitrogen 

 available, but gives rise to the development of carbon dioxide, which in turn 

 acts upon inert plant food and makes it more readily available to plants. 



Lime is also beneficial to the several forms of micro-organisms that 

 reside in the tubercles on the roots of all legumes. This may explain why 

 legumes are generally more benefited by lime than non-legumes. 



Lime Corrects Soil Acidity. — In the vast majority of instances the 

 chief function of lime is to correct soil acidity. Lime corrects acidity by 

 combining with the acids formed and giving rise to neutral salts. It will 

 seldom pay to apply lime to the soil for purposes other than this. The 

 amount of lime to apply is, therefore, determined chiefly by the degree 

 of acidity of the soil. In practice it is found advisable to apply more than 

 actual lime requirements indicated by chemical methods. This is advis- 

 able because in practice it is impossible to distribute lime thoroughly 

 and uniformly and secure its thorough mixture with the soil. Because 

 of this lack of uniformity in distribution some of the lime applied will be 

 ineffective and portions of the soil will not be brought in contact with 

 lime. It is not always necessary to make the soil neutral, since most 

 crops, even the most sensitive crops, will grow fairly well in the presence 

 of small amounts of acids. 



Sanitary Effect of Lime. — The decomposition of organic matter in 

 the soil often gives rise to products that are injurious to plant growth. 

 While these generally disappear in time, the presence of lime often corrects 

 the difficulty at once. It is also believed that plant roots excrete injurious 

 substances. Lime neutralizes these objectionable substances. 



