Crops and Weeds of Arable Land 81 



line, as replacing broad-casting. He even grew 1 3 crops of wheat on the same 

 field without manure, by fallowing alternate strips in successive years. 



Early in the eighteenth century, also, Lord Townshend founded the 

 ' Norfolk Rotation ', which did away with fallowing altogether, except as a 

 last resource in cleaning badly fouled land. Since by putting turnips after 

 wheat, the land could be hoed and thoroughly cleaned during the summer; 

 and the barley, as before, followed by clover and grass (especially Lolium 

 perenne) ; the last being ploughed in in the autumn. This 4-year system 

 remains the basis of all rotation of crops; the more so as, since 1886, the 

 value of green Leguminous crops has been increasingly recognized for increasing 

 the soil-content of combined nitrogen. Modern practice recognizes the great 

 drain of the soil by cereals, not only in combined nitrogen but in potash and 

 phosphates, and these substances may be added as chemical manures. The 

 rotation is also varied, or extended to 7-8 years, by adding another cereal 

 (e. g. oats), exchanging roots (turnips, mangel) for potatoes, keeping grass and 

 clover for more than one year, changing clover, which may be a failure, for 

 beans, or adding catch-crops after wheat for green fodder. 



A general 4-course system of wheat, roots, barley, clover and grass, may 

 thus become on heavy land a 7-year system of wheat, roots, barley, oats, clover, 

 wheat, beans, giving wheat the prominence in the succession, as it is the initial 

 factor. 



The general principle of attacking the weeds in a low and spaced crop 

 is the essential basis of rotation, and makes it a paying proposition keeping 

 the land under cultivation for food, and also maintaining a balance between 

 man and cattle. The more exact relation of the wheat-crop to the weed- 

 flora has been demonstrated at the Rothamsted Experimental Station. 1 

 Wheat has now been grown (since 1 843) continuously on the same land with- 

 out manure, and with least fallowing. On the sample | acre plot (Broad- 

 balk Field) the yield with no manure at all is still 12-13 bushels per acre, 

 an estimated diminution of ^ bushel per year representing the deterioration 

 in the fertility of the soil. Continuous cultivation on an adjacent plot, with 

 manure, maintains a high yield (to 38 bushels per acre). 



The present average yield for the entire world is given as 13 bushels 

 per acre. That of the Canadian wheat-fields 16 : for Great Britain 30: 

 for Oxford County 30 bushels and a ton of straw. The best land in England 

 will yield 40, and the maximum recorded is about 60. The present cost of 

 production runs to 15 per acre, as opposed to 5 13^. in IQI4. 2 



It follows that fallowing is wholly unnecessary if the weeds are kept down : 

 even the Rothamsted plots, drilled at 10 inches, and hand-weeded in early stages, 

 are by no means 'clean', but show a considerable undergrowth of Poppies (1922). 

 A new method of attacking the weed-problem is afforded by the use 

 of Steam Tractors : these work more efficiently than the horse-ploughs, to 

 a greater depth, and cutting 3 furrows at a time do the work of 3 horse- 

 teams, or an acre in 4 hours. By such time-saving it is possible to get all 

 the ploughing done as soon as harvest is over, instead of letting it drag on 

 into or over the winter. By steam-ploughing in August or September, the 

 stubble is broken up; and, following mild rain, the main crop of weeds 

 germinates, and may be destroyed by cultivation, before sowing. With 

 this improvement in methods of ' sterilization ', and the addition of suitable 

 manures, it will be possible to grow any crop, as required, at any time, and 

 the necessity for rotation also disappears. 3 



As compared with Wheat, Barley (Hordeum sativum) is still more xero- 



1 Memoranda of the Origin, Plan, and Results of the Field and other Experiments. Rothamsted, 

 1900, p. 30. 



2 Rothamsted Experimental Station. Abridged Report for 1918-20. 



' Loc. cit., p. 9. Where the ground is good and once clean, using clean modern seed, it is 

 possible to alternate wheat and beans indefinitely, as the weed-problem does not arise. 



F 



