202 The Rothamsted Grass Experiments. 



pared with the cereal crops, than the evidence would appear 

 to show. That it was not so may perhaps be taken to 

 indicate that, in estimating the proportion of the nitrogen of 

 the produce due to that supplied in the manure, it should not 

 be assumed that as much was derived from natural sources 

 as in the case of the unmanured produce ; but more should 

 be reckoned as derived from the manure. 



FATE OF THE FERTILISING MINERALS IN THE 



SOIL. 



Having thus somewhat fully discussed the fate of the 

 nitrogen of farmyard manure, it remains to glance ever so 

 briefly at the behaviour of the mineral constituents. 



Of the lime estimated to be supplied in the manure in the 

 eight years, only about 12^ per cent, was obtained in the 

 total produce of those years, about 9 per cent in the next six, 

 and little more than 4 per cent, in the last six years, making 

 in all only about 25 \ per cent, in the twenty years. Deduct- 

 ing the yield in the unmanured produce, however, there was an 

 increase obtained representing only 3^ per cent, of the 

 amount supplied during the first period, little more than 

 2 per cent, in the second period, and a small fraction of 1 per 

 cent, in the third period, or a total of less than 6 per cent, in 

 the twenty years. 



Of the magnesia the proportion was much larger, that in 

 the total twenty years' produce representing 70 per cent., and 

 the increased yield about 21 per cent., of that supplied. 



Of the potash the produce contained, in the three periods 

 of eight, six, and six years, 44 per cent., 22 J per cent., and 

 10J per cent., in all 77 per cent. But the increased yield, 

 over that from the unmanured plot, was only 30^-, 13, and 4J 

 per cent. ; in all, only about 48 per cent, of that supplied. 

 Pota.sh is, at any rate in moderately clayey soils, very little 

 subject to loss by drainage ; but it would appear that the 



