The Relations of Li. me to Soil Improvement, 



621 



(i.) Physioloyical effects. (a.) Lime is an essential element of 

 food for all higher plants and for many of the lower forms. It seems 

 to be especially necessary in the leaves and stems of plants for the proper 

 elaboration of starch. The total amount required is generally small, 

 althougii it differs greatly for different plants. Franke reports the per- 

 centage of lime (CaO) in a few plants as follows: 



Potato leaves 2.9% 



Potato tubers o.i % 



Pea straw . : i . 88% 



Pea seed o. 13% 



Tobacco 6. 18% 



Wood of trees 0.01-0.02% 



The amount of lime removed per acre by different crops is calculated 

 by Warrington to be as follows : 



We would call particular attention to the large use of lime by the 

 legumes, as clover and pea, because this is especially important in soil 

 improvement. 



While there is considerable need of lime as food for plants, the supply 

 of lime in the average soil is ample for those needs. It is the exception 

 when its use is necessary to furnish food-calcium. Lime has not, there- 

 fore, been recognized as a normal fertilizer constituent like nitrogen or 

 pliospborus, but rather as an aiuoidiucnt or supplement to the soil 

 mechanism. 



M). ) Lime maintains the solution of the soil in a condition of alka- 



linil\- favorable to man\- crops and micro-organisms. Most crops thrive 



in a neutral or slightly alkaHne medium ; a few plants will grow in a 



distinctly acid solution. The legumes, as clover, beans, peas, are 



