EFFECT OF MINERAL MANURES 159 



application, but without potash, since 1861, while Plot 4-1 

 receives superphosphate only. With the complete minerals 

 a fair crop is grown, averaging over Ij- ton of hay for the 

 first cut alone, and when the successive ten-year averages 

 are considered there are no signs that the fertility of 

 this plot is declining, since the production only shows such 

 fluctuations as may be put down to seasons. The reason that 

 the crop on this plot is maintained, although no nitrogen is 

 supplied in the manure, lies in the free growth of leguminous 

 plants. It will be seen that, taking the average over the whole 

 period, the leguminous plants form 24 per cent, of the herbage, 

 and the proportion has increased from year to year. These 

 leguminous plants are not only themselves independent of 

 nitrogen in soil or manure, but by fixing the atmospheric 

 nitrogen and leaving it behind in the residues of their dead 

 roots, they provide a supply for the grasses and other plants 

 which cannot of themselves feed on the nitrogen of the air. 

 The predominant leguminous plant is Lathyrus pratensis, but 

 Red Clover is also abundant. A large number of species of 

 grasses are represented on the plot, none of which are specially 

 prominent. Amongst the weeds, Knapweed is fairly abundant, 

 and there is also a rather large proportion of Yarrow. The 

 general aspect of the vegetation is shown by the photograph 

 of turf, Fig. 20. 



The omission of potash on Plot 8 has caused a very 

 striking difference both in the crop and in the character of the 

 herbage. The average crop has been about one-quarter less 

 over the whole period, and shows a progressive decline in 

 fertility, until at the present time it is little more than half 

 that of Plot 7. The poor results on this plot, as compared 

 with Plot 7, must be put down to its poverty in leguminous 

 herbage, the development of which seems to depend on a free 

 supply of potash. Of late years the proportion of leguminous 

 plants on this plot has amounted to about one-half of that 

 found on Plot 7, the grasses are about the same, the difference 

 being made up by an increased amount of weed. The 



