NITROGEN GAINED OK LOST 



209 



V. GAIN OR Loss OF MANURIAL CONSTITUENTS TO THE LAND. 



From the analyses which have been made from time to 

 time of the crops on Agdell field it is possible to estimate the 

 quantities of the chief manurial ingredients nitrogen, phos- 

 phoric acid, and potash which are removed from the soil 

 during a typical rotation. Thus we can form some idea of 

 what will be necessary to maintain the fertility of land under 

 ordinary crop, and whether there are any natural recuperative 

 agencies which restore plant food to the soil. 



Table LXXIII. shows the amount of nitrogen removed per 

 acre per annum on the three plots which are fallowed and 

 where also the roots are carted off where everything is, in 

 fact, removed, and no nitrogen is added except in the one case 

 on Plot C where the Swedes are manured. 



TABLE LXXIII. Nitrogen removed "by Crops grown in rotation, Agdell Field. 

 Average of eight Courses, 1852-1883. Roots carted. 



It will be seen that on the unmanured plots the removal of 

 nitrogen is chiefly effected by the two cereal crops, so small 

 has the crop of roots become. The average loss of nitrogen 

 over the whole four years of the rotation amounts to just 

 over 19 Ib. per acre per annum, which agrees very closely 

 with the average annual removal of nitrogen from the 

 unmanured plot in Broadbalk where wheat is grown year 



after year. When mineral manures are used for the Swedes 



o 



