176 The Rothamsted Grass Experiments. 



Of hay, the average produce per acre per annum over the 

 twenty years was : without manure, 23831b. ; with ammonia- 

 salts alone, 29461b. ; with ammonia-salts and superphosphate 

 (seventeen years), 38371b. ; with ammonia-salts and mixed 

 mineral manure, with potash for six years, and without 

 potash fourteen years, 51741b. ; and with ammonia-salts and 

 the mixed mineral manure, including potash every year, 

 57111b. 



It is remarkable that there was, over the twenty years, 

 almost identically the same amount of nitrogen taken up 

 where the potash was discontinued as where it was continu- 

 ously applied, and during the period of the omission there 

 was even rather more. But of mineral matter, about one-fifth 

 less has been taken off, over the fourteen years, in the crop 

 grown without than with potash ; and the falling off in amount, 

 compared with the earlier period, is nearly 42 per cent, with- 

 out, against only 25 per cent, with, the potash. Still, on 

 plot 10 there was much less hay produced, and much less 

 mineral matter taken up, than on plot 9, where the applica- 

 tion of potash was continued. 



It appears that, on plot 10, there was a considerable 

 residue of potash remaining after the six years' application ; 

 that this was yielded up less freely than that from fresh 

 supplies, but more freely in the earlier than in the later years ; 

 and that at the end of the fourteen years a residue still 

 remained, of which some still continued to be yielded up. 

 That this should be so is quite consistent with results 

 obtained on arable land, which, as already referred to, show, 

 both in the amounts of crop and in its chemical composition, 

 the effects of a residue of potash applied more than twenty- 

 five years previously. Supposing, however, that in the 

 presence of an artificial supply of potash less was yielded up 

 from the soil itself, the residue remaining would of course 

 be by so much less than 2001b. at the end of the fourteen 

 years. 



About an equal number of species, and nearly the same 



