16 RESULTS OF EXPERIMENTS AT ROTHAMSTED, 



Or if, instead of taking the average of the 32 years, we take it only 

 over the 26 years in which there was any Bean crop, the average total 

 produce was without manure 1,709 Ibs., with purely mineral manure 

 2,688 Ibs., and with the mineral and nitrogenous manure together, 

 3,086 Ibs. ; that is, there was an annual average increase of 979 Ibs. by 

 the mineral manure containing potash, and of only 398 Ibs. more by 

 the addition of nitrogenous manure. 



The details further show that without manure, the total produce 

 of two of the last 8 years was only exceeded three or four times during 

 the whole period, namely during the first five years ; with mineral 

 manure alone, the total produce of 2 of the last 8 years was only 

 exceeded four or five times ; and with the mineral and nitrogenous 

 manure together, the total produce of 2 of the last 8 years was only 

 exceeded six times. Indeed, on both of the manured plots, the average 

 total produce over the last 4 years of actual crop, was nearly as much 

 as the average of the first 8 years of crop. Thus, with the purely 

 mineral manure, the average total produce of the first 8 years was 

 3,208 Ibs., and over the last 4 years of crop it was 3,011 Ibs., and with 

 the mineral and nitrogenous manure, it was over the first 8 years 

 3,555 Ibs., and over the last 4 years of crop 3,292 Ibs. It will be seen 

 further on, that the average annual yield of nitrogen was also nearly 

 as great over the last 4 years, as over the first 8 years, of. crop. 



It may be observed that nitrogen supplied as ammonium-salts to 

 the highly nitrogenous Leguminous crops, seldom gives any increase, 

 and is sometimes injurious, in the year of application ; though some 

 benefit may afterwards result from the residue after the ammonia has 

 been converted into nitric acid. Even nitrates, however, directly 

 applied as manure, are very uncertain in their action, and at any rate 

 yield very much less increase of produce with the highly nitrogenous 

 Leguminosse, than with the Graminese, and crops of other families, 

 yielding produce of low percentage of nitrogen in its dry substance, 

 and appropriating comparatively little nitrogen over a given area of 

 land. 



To this point I shall have to refer in some detail further on, but in 

 the meantime it is to be specially noted, that whilst the Cereal crops 

 may be successfully grown for many years in succession on the same 

 land, provided only that mineral and nitrogenous manures are liberally 

 supplied, the Leguminous crop Beans, gradually fails when so grown ; 

 and although characteristically benefited by mineral manures containing 

 potash, neither these alone, nor a mixture of mineral and nitrogenous 

 manure, has sufficed to maintain even fair growth for a number of 

 years in succession. 



The result is, however, not entirely due to deficiency in the supply 

 of constituents within the soil, but is also in a considerable degree 

 dependent on the fact that, by the continuous growth of the crop, 

 with its special habit, and range of roots, the surface soil acquires a 

 close and unfavourable condition, and a somewhat impervious pan is 

 formed below. The improved result in the later years, with the inter- 



