174 



SYSTEMS OF PERMANENT AGRICULTURE 



The amount and frequency of subsequent applications will de- 

 pend upon the rate of loss by leaching and by removal in crops. 



The soil of the Rothamsted Experiment Station, England, is 

 underlain with a bed of calcium carbonate, in the form of chalk, 

 at a depth of 8 feet or more; but, nevertheless, the overlying residual 

 soil material is normally deficient in limestone to a depth of several 

 feet. A century or more ago certain fields were given heavy appli- 

 cations of chalk, dug out of pits excavated for the purpose, and the 

 fact that some of these fields still contain 50 tons of calcium car- 

 bonate per acre in the plowed soil and continue to produce good 

 crops, with fair treatment, is proof sufficient that there is no 

 danger of applying too much ground limestone. 



During a period of 40 years, from 1865 to 1905, large numbers of 

 analyses have been made of the Rothamsted soils. During that 

 time, according to Director Hall and Doctor Miller (Proceedings of 

 the Royal Society, 1905, Vol. 77), there have been the following 

 losses of calcium carbonate from nine different plots on Broadbalk 

 Field, where wheat is grown every year: 



TABLE 27. LOSSES OF CALCIUM CARBONATE FROM BROADBALK FIELD, 

 ROTHAMSTED, FROM 1865 TO 1905 



The loss of calcium carbonate during the period of 40 years 

 ranges from 11.3 to 28.6 tons per acre. The average annual loss 

 where ammonium salts have been applied is 1170 pounds, but with 

 no ammonium salts the average loss is only 710 pounds a year, or 

 about one ton per acre in three years. 



