WHEAT GROWN CONTINUOUSLY 41 



wheat year after year on the same land for at least sixty years 

 without any decline in the productiveness of the soil, provided 

 an appropriate manure be supplied to replace the nitrogen, 

 phosphoric acid, and potash removed by the crops. There is 

 no evidence in fact that the wheat gives a smaller yield when 

 following a long succession of previous wheat crops than when 

 grown in rotation, although the vigour of the plant does not 

 appear to be so great. The real difficulty, however, in con- 

 tinuous corn-growing is to keep the land clean ; certain weeds 

 are favoured by the wheat and tend to accumulate, so that the 

 land can only be maintained clean by an excessive expenditure 

 in repeated hand-hoeing. Notwithstanding all the labour that 

 is put on the plots, the " Black Bent " grass, Alopecurus agrestis, 

 has from time to time become so troublesome that special 

 measures have had to be taken to eradicate it and to restore 

 the plots to a reasonable degree of cleanliness. 



How little the wheat plant is able to survive when in 

 competition with weeds, may be seen from a portion of the 

 Broadbalk field where the wheat crop in 1882 was allowed to 

 stand and shed its seed, the soil not being cultivated in any 

 way. In the following season a fair wheat plant came up and 

 gave about half a crop, but after it seeded the weeds increased 

 their hold upon the ground until in the fourth season only two 

 or three stunted wheat plants could be found, which have never 

 reappeared since. The fundamental importance of cultivation 

 and the suppression of weeds is further to be seen in the 

 returns from the continuously unmanured plot. This piece of 

 land at the beginning of the experiments was not only in poor 

 agricultural condition but had been under arable cultivation for 

 at least two or three centuries, and was therefore far removed 

 from the condition of virgin soil with its accumulation of 

 fertility, and yet by cultivation alone it has been able to grow 

 for sixty years a crop averaging 13 bushels to the acre. This 

 is almost the average crop produced in the United States, and 

 is very similar to the general average production of the great 

 wheat-growing areas of the world. Nor is there, as far as can 



