Scientific A griculture 



132 



[August, 1910. 



without the introduction of any ex- 

 traneous source of nitrogen. 



Such, indeed, was the state of affairs 

 in Europe prior to the discovery of arti- 

 ficial manures and foods ; the farm had 

 to be self-supporting, the nitrogen that 

 came back to the land in the farmyard 

 manure had all been taken from the 

 land previously ; it was less than that 

 which left the land by the amounts in 

 the corn, meat, milk, and wool sold off 

 the farm, and by all that was lost and 

 wasted in making the farmyard manure. 

 These losses were, however, so far 

 balanced by the gains of nitrogen due to 

 bicterial agencies that the fertility of 

 the soil at its low level remained 

 unimpaired; e.g , there is evidence that 

 the average production of wheat in the 

 south and east midlands of England had 

 remained at about 20 bushels per acre 

 for a long period up to the early years 

 of the nineteenth century. That the 

 laud can attain such an equilibrium of 

 production and fertility is indicated 

 by some of the results obtained on 

 the Agdell Field at Rothamsted, where 

 a four-course rotation of swedes, 

 barley, clover or bare fallow, and wheat 

 is followed. The experiment started in 

 1818, and since that time the soil has 

 been analysed in 1867, 1874, 1883, and 1909. 

 For our purpose the instructive plot is 

 that which receives no nitrogen as 

 manure, but minerals, i.e., Phosphoric 

 acid and potash, once in each rotation ; 

 it is divided into four sub-plots, two on 

 which clover (or beans) is grown before 

 the wheat, two on which there is a bare 

 fallow ; one each of these two again has 

 the swede crop returned to the land, 

 whereas on the other it is carted away. 

 The following table shows the percent- 

 age of nitrogen in the surface soil 

 (9 inches) at the respective dates, to- 

 gether with the average crops on each 

 ploc over the period 1852-1903 :— 



Nitrogen per cent, in Soil of Agdell 



Field, Rothamsted. 



The Plots all receive Mineral Manures, 

 but no Nitrogen, 





Fallow. 



Clover. 





Roots 

 carted 



off. 

 13/U. 



Roots 

 returned. 

 9/10, 



Roots 

 carted 

 off. 

 15/16. 



Roots 

 returned. 

 11,12. 



1867 

 1S74 

 1c 83 

 1909 



0-1224 

 0-1147 

 O'llBl 

 0-1159 



1240 

 0*1238 

 0-1228 

 0-1195 



0'1327 

 0*1241 

 G-1329 

 0-1347 



0-1380 

 0-1321 



O-lSt-3 

 0-1498 



1852-1003 

 Wheat average 

 Clover ,, 

 Swedes ,, 

 Barley „ 



31'2 bushels 



i51-0 cwt. 

 22*1 bushels 



32'2 



2«8 

 . 28-7 



32-2 



4 1*0 cwt 



160 



24*5 



35*1 

 47*7 

 187 

 34-5 



The changes indicated in the amount 

 of nitrogen in the soil are not large, 

 being, indeed, very close to the ex- 

 perimental error ; but, reviewing the 

 numbers altogether, it may safely be 

 concluded that the first plot, 13/14, from 

 which the roots carted and where no 

 clover is grown, is declining in fertility. 

 The two plots 9/10 and 15/16 are practi- 

 cally stationary ; if anything, 9/10 with- 

 out clover may be losing ground, where- 

 as 15/16 with clover, but fiom which the 

 roots are carted, may be gaining ground ; 

 while the plot 11/12, on which both 

 the roots are returned, and clover is 

 grown, is still more probably gaining 

 a little fertility. This last plot has 

 yielded on the average over 52 years 

 35 bushels of wheat, 34 bushels of barley, 

 over 9 tons of swedes, and nearly 2£ tons 

 of clover hay per acre, which is nearly 

 equal to, it anything higher than, the 

 average production of the whole of 

 Great Britain during that period. Such 

 a yield, which, though equal to the 

 average, may be taken as lower than 

 a good farmer would expect from that 

 class of land, has been obtained with- 

 out bringing in any external source 

 of nitrogen, without even returning to 

 the land all that would come back under 

 ordinary conditions of farming. In 

 practice it would not always be possible 

 to feed off the root crop on the land, and 

 even then not so much carbonaceous 

 material would be returned as is the 

 case in the experiment, where it has been 

 necessary to cut up the roots and plough 

 them in, but, on the other hand, the 

 manure made from the straw of both the 

 wheat and barley crops and from the 

 clover hay would also come back to the 

 land. 



The evidence provided by this plot is 

 strengthened by the results obtained 

 on the three other plots, on which the 

 recuperative operations of clover grow- 

 ing, and returning the roots to the land, 

 are either singly or together omitted ; 

 under such conditions the gross produc- 

 tion is distinctly less, and the fertility 

 of the land is stationary or declining very 

 slowly, so that an equlibrium at a lower 

 level of production has been or will 

 shortly be attained. 



We may then conclude from these 

 Agdell Field results that a conservative 

 system of farming on the four-course 

 system, in which clover is grown at least 

 once in every two rotations, in which 

 the roots are consumed on the land, and 

 the dung made by the straw and hay 

 comes back to the land will maintain 

 the fertility df the soil and support for 

 an indefinite period a gross production 

 at about a 4 qr. of wheat per acre level 



