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The American Class
出版U.S. Department of Agriculture, 1923
URLhttp://books.google.com.hk/books?id=g3hX0AEACAAJ&hl=&source=gbs_api
註釋"Red clover is the most important leguminous forage and soil-improving crop in the northeastern quarter of the Unites States. It will grow on any well-drained fairly rich soil that has plenty of lime in it . Without lime or on hard run-down land in which the organic matter has been exhausted by bad cropping, it will not thrive. The most common method of seeding is on winter grain, but it also is often seeded with spring grain. Late summer seeding is successful in much of the southern and eastern part of the clover area. Red clover is most often seeded with timothy though sometimes with other grasses. With timothy the hay of the first crop year is mostly clover; the second year the timothy is most heavy and after that the clover largely disappears. Clover is most used in rotations with a cultivated crop and a small-grain crop in three, four, and five year rotations. Root borers and other insects as well as fungous diseases make it undesirable to keep a field of pure clover more than one crop year. The use of high quality seed of American production is strongly advised. Imported seed is often unfit for use in the United States, and seeding it is always risky. The secret of haymaking consists in the rapid removal of the moisture form the cut plants without killing the leaves prematurely. Seed is usually taken from the second crop. The yield is always more or less uncertain, a nd over much of the clover area it is cut down more by the clover-flower midge and the clover-seed chaleis fly than by any other factor. The injury caused by these insects can be minimized by cutting the first crop a little earlier than is usually done."--Page ii.