170 EXPERIMENTS UPON GKASS LAND 



being barely perceptible. In 1903 the leguminous plants had 

 risen to over 40 per cent, of the herbage, but the weeds had 

 not altered much. The change, as is seen in the diagram, did 

 not take place at once, the leguminous plants requiring nearly 

 twenty years to spread and establish themselves; after five 

 years, for example, they constituted less than 5 per cent, of the 

 herbage. The photograph, Fig. 30, shows how closely the 

 herbage on this plot now resembles that on Plot 7, which has 

 never had anything but minerals. 



On Plot 15 nitrate of soda was used up to 1875, when the 

 nitrate was dropped and a change was made to the same 

 complete mineral manure as is used on Plots 6 and 7. At the 

 time of the change the grasses constituted 80 per cent, of the 

 herbage and the rest was weeds, the leguminous plants being 

 again almost imperceptible. At the present time this plot is 

 almost identical in aspect with the one previously described 

 and with Plot 7 which has received only mineral manures 

 from the beginning ; it contained in 1903 about 50 per cent, of 

 grass and 30 per cent, of leguminous plants. The photograph, 

 Fig. 31, shows that Lathy rus is more prominent than the 

 clovers. The change in the herbage on this plot took place 

 rather more rapidly than on the plot which had received 

 ammonium- salts beforehand, being practically complete in ten 

 years. 



Plot 8 had received mixed mineral manure containing potash 

 up to 1861, by which time the herbage had become largely 

 leguminous, as on the adjoining Plot 7. The potash was 

 dropped in 1862, though the superphosphate, magnesia, and 

 soda have been continued. The effect of the absence of 

 potash was seen very quickly, the proportion of leguminous 

 plants dropping from 20 to about 9 per cent, in the first 

 five years. Owing to the continued manuring with phosphoric 

 acid and the lack of potash, this plot has become seriously 

 impoverished, and is now very little better than Plot 4-1 which 

 has received superphosphate only since the beginning of the 

 experiments, the weeds constituting about one-third of the 



