96 



RESULTS WITH POTATOES 



and then bouted ; the potatoes are then sown in the furrow, 

 which is lastly converted into a ridge. On the farmyard manure 

 plots the dung is laid in the furrow before planting the potatoes. 



The kinds of potatoes grown during the experiments were :- 

 Rock, four years ; Champion, eleven years ; Abundance, five 

 years. 



The results yielded by the various manures during 20 years 

 are given in Table XXXI. 



TABLE XXXI. 



PRODUCE OF POTATOES VARIOUSLY MANURED AT ROTHA'MSTED 

 DURING TWENTY YEARS, 1876 95. 



We see from the results in the table that the produce on 

 every plot has very considerably fallen off in the course of the 

 experiment, except in the case of the plot receiving farmyard 

 manure each year. The explanation is probably to be found 

 in the fact that the potato is a crop which leaves scarcely any 

 residue of vegetable matter in the soil. By the continuous 

 cultivation of potatoes with purely artificial manures the soil 

 thus loses its stock of humus, and where the soil is heavy, as 

 at Rothamsted, it gradually deteriorates in physical condition. 

 The results obtained during the first ten years of the experi- 

 ment will represent best the return from manures which may 

 be expected with an ordinary agricultural condition of the land, 

 and to this portion of the results we shall therefore chiefly refer. 



The increase given by a full supply of ash constituents alone 

 (plot 10) is seen to be very considerable, amounting in the first 

 ten years to 38 cwts. of potatoes. We have in this case, as in 



