Table III. Gypsum or Land Plaster. 



Note: Gypsum does not neutralize sour soils. 



The Use and Function of Lime in Agriculture. 



The great majority of Massachusetts soils through many years of use contain 

 acid reacting residues which may unfit them for maximum production. In the 

 absence of natural alkaline soils in New England, it may be said that most of 

 our soils that do not respond with satisfactory crops following the liberal use 

 of farm manures and fertilizers would benefit by a treatment that would change 

 the soil reaction to a less acid condition. The most convenient method of accom- 

 lilishing this result is by the use of lime furnished in the abundant and con- 

 veniently located lime deposits of our section. 



It may be pointed out that the use of certain basic fertilizers, such as nitrate 

 of soda and basic slag phosphate, tends to prevent the occurrence of extreme 

 acid condition of soils. Their purchase, however, at very much of a premium 

 over equally effective nitrogen and phosphorus products as sources of plant food 

 might be questioned, in view of the relatively low cost of agricultural lime 

 products which are always effective in reducing soil acidity. 



There are several methods of measuring the acid reaction of soils, or, as it is 

 sometimes expressed, the lime absorption capacity of soils, such as the Hopkins, 

 the Veitch, the Truog, and the Jones methods, not to mention various colori- 

 metric methods which are largely based upon the hydrogen ion concentration 

 or pH value of the soil solution. 



Aside from its acid neutralizing effect, other benefits are likely to follow the 

 use of lime on acid soils having a low response to farm manure and fertilizer. 

 The more prominent of these are briefly mentioned as follows: 



Lime products high in both calcium and magnesium oxides furnish both of 

 these plant food elements in available form. Indications have been recently 

 noted of magnesium shortage in a few Massachusetts soils, particularly where 

 tobacco has been the dominant crop for many years. This condition is usually 

 referred to as sand drown. Observations as to magnesium shortage have also 

 been noted on certain plots under experiment at this Station. 



It may be appropriate at this time to give to magnesium oxide the greater ad- 

 vantage which it possesses in its acid neutralizing effect, due to the lower mole- 

 cular weight of its compounds. The percentage of magnesium oxide multiplied 

 by the factor 1.39 will give the neutralizing equivalent of calcium oxide. It 

 should be pointed out that large applications of magnesia will prove injurious 

 to vegetation. It is not likely, however, that an application of five to six tons 

 per acre of a magnesian limestone, followed every four to five years by a two- 

 ton application, would ever produce injury. 



Liming hastens the decomposition of existing organic matter in the soil, thus 

 liberating much of the nitrogen which is associated with it. Liming also pro- 

 duces a better environment for nitrifying bacteria, and the presence of lime 



