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Page:Popular Science Monthly Volume 73.djvu/415

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411
THE ROTATION OF CROPS

spot disease (Cercospora beticola) was prevalent. In 1901 the crop was sown on these and on plats which had been in corn in 1903 and other crops previously. The disease attacked the beets on the "no rotation" plats early in the season, and many rows had to be resown. The yield per acre was 9.5 tons containing one ton of dry matter, value $20. The yield per acre on the rotation plats was 3312 tons containing four tons of dry matter, value $80, a clear gain of $60 per acre from the rotation of crops.

Different crops require different amounts of water to make a pound of dry matter, that is, some transpire more than others, thus oats will transpire 500 pounds, potatoes and corn about 300 pounds, barley about 100 and clover frequently over 600 pounds. From this it will be seen that the Maine farmer is wise because he is discounting the season, when he sows oats the year after potatoes in his rotation of clover (two years), potatoes, oats; thus a light water consumer is placed between two heavy consumers. This is important since water is generally the factor which controls the yield of crops. At Eothamsted, England, where wheat has been grown for 60 years on the same piece of land without manure or fertilizer, the average yield per acre is about 1212 bushels, while on land in a rotation—but otherwise similarly treated—the average yield was about 26 bushels. During the last 52 years the total yield of wheat is 665 bushels, which at 75 cents per pushel is worth $198.75. That of continuous barley growing, also without manure or fertilizer, during the same time, was 868 bushels worth $131 at 50 cents a bushel. When wheat and barley were grown in rotation with roots and clover or beans, without manure or fertilizers, the yields and values of the 13 crops of each were roots 9.5 tons, $19; barley 333 bushels, $166.50; clover (5 crops) 1.12 tons, $44.20; beans (8 crops) 101 bushels, $101; wheat, 335 bushels, $251.25; a total of $591.95.

The income from the land under this system is in favor of the rotation. It is $96.20 or 19 per cent, ahead of continuous wheat farming and $150.95 or 31.75 per cent, ahead of continuous barley farming.

Scientists have been kept busy explaining why we should get better yields from a rotation of crops. De Candolle over 100 years ago suggested that plants excreted a poisonous substance which rendered the soil objectionable to others of the same species, a theory which is again coming into some prominence. The continuous culture of wheat and barley at Rothamsted was undertaken partly to test this. Experiments now being conducted at Woburn Fruit Station, England, show that grass injures fruit trees, and it is claimed that the injury seems to be due to some poisonous substance, either direct or due to bacteria. Liebig suggested that plants tended to exhaust the soil by the removal of different ingredients and that as some plants took more of one in-