LIMING THE SOIL 381 



this compound was of greater value than either ground lime- 

 stone or slaked lime as an amendment. He also concluded 

 that silicon was an essential element in plant nutrition. Hart- 

 well and Pember/ in 1920, found di-calcium silicate approxi- 

 mately equal to limestone insofar as the correction of acidity 

 was concerned. Lettuce was used as an indicator. They 

 found no indication that the silicon was of any value, but, as 

 their experiments were with soil, this, of course, does not op- 

 pose the idea that silicon is an essential element in the growth 

 of plants. 



Hartwell and Pember concluded that the beneficial influ- 

 ence of phosphorus and calcium compounds added to the soil 

 might, in many cases, be due to the precipitation of active 

 aluminum quite as much as to the supplying of nutrients or 

 the correction of actual acidity. Such a conception of the 

 influence of liming materials may ultimately mean an in- 

 crease in the number and nature of the compounds that may 

 be used as soil amendments. 



208. Importance of lime in soil improvement.^ — The in- 

 fluence of successively liming a soil over a period of years 

 may tend to raise or lower the fertility of the soil, according 

 to the system of soil management that accompanies the appli- 

 cations of the lime. The use of lime alone will undoubtedly 

 increase crop yield for a time. Basic exchange will be en- 



^ Hartwell, B. L., and Pember, P. E., The Bfect of Dicalcmm Silicate 

 on an Acid Soil; Soil Sci, Vol. X, No. 1, pp. 57-60, July, 1920. 



*A number of general references on the importance of lime were 

 given at the beginning of the chapter. See also, 



Wiancko, A. T., et at, The Value of Lime on Indiana Soils; Ind. Agr. 

 Exp. Sta., Bui. 213, 1918. 



Stewart, R., and Wyatt, F. A., Limestone Action on Acid Soils; 111. 

 Agr. Exp. Sta., Bui. 212, 1919. 



Lipman, J, G., and Blair, A. W., The Lime Factor in Permanent 

 Soil Improvement; Soil Sei,, Vol. IX, No. 2, pp. 83-114, Feb. 1920. 



Hartwell, B. L., and Damon, S, C, Siaa Years' Experience in Improving 

 a Light XJnproducrtive SoU; Jour. Amer. Soc. Agron., Vol. ISj No. 1, 

 pp. 37-41, Jan. 1921. 



