ON RECENT DEVELOPMENTS IN AGRICULTURAL SCIENCE, 271 
Taste IIT. 
Average Amounts of Dry Matter and Nitrogen in Total Produce of 
Various Crops, grown without Manure at Rothamsted. 
Dry Matter Nitrogen’ 
Averages Over 
10 Years|10 Years|10 Years 10 Years 10 Years Wigs ae ms 
1852- | 1862- | 1872- | 1882- | 1892- |“ eras 
1861 1871 1881 1891 1901 
lb. Ib. lb. lb. lb. lb. lb. 
Broadbalk Wheat . | 2,199 | 1,791 | 1,346 | 1,480 | 1,514 | 1,666 17-0 
Hoos Barley . | 2,352 | 1,797 | 1,303 | 1,229 | 1,120 | 1,560 15°3 
Agdell Rotation! . | 2,321 | 1,817 | 1,403 | 1,644 | 1,295 | 1,696 | 17°6 
Park Hay? . | 2,082 | 2,144 | 2,196 | 1,421 | 1,961 33°8 
Carted fallow portion. First and second crops. 
Table III. shows the average yield during the last five. decades of dry 
matter and of nitrogen from four of the unmanured plots at Rothamsted ; 
it will be seen that the difference in the production during the last as 
compared with the second period of ten years is no more than would be 
covered by seasonal variations. In other words, the yield, which, as 
we learn in other ways, is mainly determined by the amount of available 
nitrogen, has reached a state of equilibrium when the resources of the soil, 
the material brought down by the rain, and the nitrogen-fixing agencies 
taken together are just equal to providing the crop with about 17 lb. of 
nitrogen per acre per annum in addition to the unknown amounts 
removed by drainage and in the weeds. The small amount of fixation 
this indicates and the corresponding low level of production must be set 
down to the lack of combustible carbohydrate, due to the very complete 
removal of the various crops from the soil, since the root and stubble left 
behind after the growth of a cereal crop amount to but a small fraction 
of the total produce. 
In the case of grass-land the conditions are entirely different, 
especially when we are dealing with wild prairie or forest, where the 
annual growth of carbohydrate falls back to the soil and is available for 
such organisms as the Azotobacter. At Rothamsted two plots of land 
which were under arable cultivation twenty-five years ago have been 
allowed to run wild and acquire a natural vegetation of grasses and 
weeds, subject to no disturbance beyond the occasional eradication of 
scrub and bushes. Samples of the soil taken when the land was still 
under the plough have been preserved, and the comparison of these with 
new samples drawn during the last year shows enormous accumulations of 
nitrogen, even when every allowance has been made for certain inevitable 
errors in sampling the soil (see Table IV.). Of these two fields the Gees- 
croft plots are the more interesting, for though showing the gain of 
nitrogen is less (45 lb. per acre per annum against 98 Ib. on Broadbalk) 
yet continued observation of the herbage that has sprung upon this 
field has shown the absence of any leguminous plants, According to a 
botanical analysis made in 1903 the leguminous plants only constituted 
0:4 per cent. of the vegetation (as weighed in the dry state) on the Gees- 
