CHAPTER XII 

 LIME 



Nitrogen, phosphorus, and potassium compounds are 

 direct or food fertilizers primarily. It is for their food value 

 to the plant that they are purchased. Calcium compounds, 

 on the other hand, are usually considered as indirect ferti- 

 lizers or amendments. Calcium is, of course, an essential 

 element in the growth of plants, but the effects of compounds 

 of calcium on the soil, and the exploitation of these effects 

 has given calcium an importance for other than feeding 

 purposes. As a plant food, however, calcium is frequently 

 necessary in soils, especially for certain crops, and it is 

 necessary to consider calcium in this connection, without 

 at all minimizing its effect as an amendment. 



185. Calcium Fertilizers as Plant Food. — The total amount 

 of calcium in soils of course varies considerably, but on the 

 average is not as much as that of potassium — 0.5 to 1.50 per 

 cent. In many cases it may be present in part as calcium car- 

 bonate which is fairly soluble in soil moisture, but most of 

 it is in silicate and organic form and may be very insoluble. 

 Since calcium carbonate is so soluble, it very frequently 

 happens that this compound is entirely lacking even in 

 limestone soils. As a result, soils may lack sufficient available 

 calcium for the nutrition of crops. 



Some farm crops do not need very much calcium, it is 

 true, but other crops like clover and alfalfa do need large 

 quantities. Table XII shows the amount of calcium oxide 

 removed by various crops. Of course, this represents the 

 amount removed only, and not the whole amount needed, 

 for plants at harvest do not remove as much as they need 

 during their growth. 



