230 SOIL ACIDITY AND LIMING 



structure, and hence favors the development of good tilth; (/) 

 weeds can be better controlled. 



Calcium is to be regarded as an important plant-food element, 

 particularly in growing alfalfa, clover, peas, etc. Alfalfa fails on 

 an ordinary acid soil because it cannot secure sufficient calcium to 

 meet its needs. Such crops as corn and grain, on the other hand, 

 may grow quite well on acid soils, because there is still sufficient 

 calcium in such soils to supply the needs of these crops (table on 

 page 62; Figs. 149 and 156). 



Any acids formed in soils through natural processes are neu- 

 tralized by lime if it is present. In soils certain substances other 

 than acids may be formed which may prove injurious if allowed to 

 accumulate. Lime destroys the poisonous effect of many of these 

 substances. The helpful soil organisms especially are injured 

 when soils become acid. Most of them favor soils that are suffi- 

 ciently supplied with lime. This explains why it is best to lime an 

 acid soil before it is inoculated, particularly for alfalfa. 



It has been shown that plant-food elements are more available 

 in non-acid than in acid soils.- This is especially true in the case 

 of phosphorus. Often in a field of uniform silt loam, for example, 

 crops suffer for want of phosphorus on acid areas, while on the 

 areas not acid a phosphorus deficiency is not manifested 

 even though the acid soil contains more total phosphorus than 

 the non-acid areas. Acid soils are generally in need of phos- 

 phate fertilizers. 



It is wise economy to lime an acid soil if for no other reason 

 than to enable the soil to give greater returns from manure and 

 fertilizers. Some interesting results from the Ohio Station are 

 presented in the following table. These are the results of an experi- 

 ment extending through twelve years in a five-year rotation of 

 corn, oats, wheat, clover and timothy, on an acid, long-cropped 

 soil. This experiment is being continued. 



These results, and many others, plainly show that liming is 

 the first step in the improvement of an acid soil. 



When crops like alfalfa and clover fail, or are poor and thin 

 because of soil acidity, weeds have a better chance to grow, owing 

 to the fact that they meet with little or no competition. On the 

 other hand, when alfalfa and clover grow thick and strong under 

 favorable conditions as regards lime, etc., the weeds are smothered. 

 Sheep sorrel, or field sorrel, thrives especially well on acid fields 

 in which clover or alfalfa fails. 



