EXTEisrsioisr cotjese iisr soils. 63 



derived by glaciation from limestone rocks are foimd to be more or 

 less acid. Liming is the only practical way for correcting acidity. 

 It is also beneficial to the soil in several other ways. Nearly all of 

 the vast area of sandy lands of the South, and much land of the 

 North and Northeast, as well, need liming. Besides other related 

 topics, there will be taken up in this lesson the means for detecting 

 soil acidity, together with the different kinds of lime, the quantity 

 of each to be used on the soil, and the methods of application. 



Lime is not generally considered as a fertilizer, although calcium, 

 the mineral element of lime, is present in certain soils to such a limited 

 extent that some substance containing this element needs to be 

 added as a plant food. 



Reasons for soil acidity. — While the question of acidity is still 

 under investigation, the following reasons for this condition in soils 

 seem to be fairly well established: (1) The abnormal breaking down 

 of large quantities of vegetable matter in lowlands poorly drained 

 causes acidity. (2) Because of the greater water solubility of the 

 basic compounds of the soil than of the acid silicates, the bases are 

 removed more rapidly from leaching than are the acid compounds. 

 Since cultivated areas leach more readily than wooded and pasture 

 lands, they thus develop acidity more rapidly. (3) In cropping, the 

 basic elements of plant food are taken more rapidly from the soil 

 than are the acid elements. When crops are removed from the land, 

 therefore, instead of being fed and the manures returned, an acid 

 condition eventually results from this cause. Moreover, the basic 

 elements are carried from the subsoil to the surface to some extent 

 by the roots of plants, and it is a common experience to find the sub- 

 soil acid when the surface is still neutral or alkaline. (4) An acid 

 residue is left in the soil from some fertilizers. Ammonium sulphate, 

 for example, when applied to the soil gives up ammonia as a plant 

 food and leaves sulphuric acid as a residue. It is thought, likewise, 

 that when potassium sulphate is used in fertilizers, a part of the 

 potassium becomes liberated, leaving an acid salt of potassium in 

 the soil. 



Ohjections to acidity (Ref. No. 7, p. 141). — Nitrification of organic 

 matter does not take place readily in acid soils, although in the case 

 of acid marsh soils which are well drained, the nitrification may be 

 sufficient to supply nitrates for the rapid growth of most crops. 

 Acidity in the soil, moreover, has much more detrimental effects in 

 its influence on nitrogen fixation by certain tubercle-forming organ- 

 isms than on the process of nitrification. The bacteria which form 

 tubercles on medium red clover, alfalfa, sweet clover, soy beans, and 

 some other legumes do not develop at all rapidly in acid soils, and 

 when the soils are quite acid it is necessary to use lime to correct 



