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483. Army, T.J. and J.C. Hide. 1959. Effects of green manure crops on dryland wheat production in the Great Plains area of Montana.. Agron. J. 51:196-198.
This paper summarizes the results from the green manure treatments which were a part of a 38-year study (1914-1951) of numerous small grain rotations involving wheat, barley, oats, corn, and fallow in various combinations. The rotation experiments were carried out at several Great Plains experiment stations including Havre, Huntley, and Moccasin, Montana, and Sheridan, Wyoming. The results indicated that winter rye, field pea, and sweetclover green manures had no effect at all or a depressing effect on small grain yields the following year as compared to ordinary fallow. The results of this unreplicated study are the most likely reason that research on dryland legume-cereal rotations essentially ceased in Montana until 1978. Although legume green manures, ideally, may impart several beneficial effects on ensuing cereal crops, the primary benefit is the release of symbiotically fixed nitrogen. The legume green manures in the long-term study at Moccasin and Huntley had little chance of improving wheat yields compared to ordinary fallow for several reasons. First, the soils involved, and most Montana soils indeed, had not yet become deficient in N as they are today. Organic matter had begun to decline by the 1950's but it still provided ample N to meet the needs of wheat yield potentials of that era. Also, the management of the legumes in these early studies is questionable as one passage from the report suggested that when the green manure crops were not successfully established, thee was invariably a good crop of Russian thistle (Salsola kali L.) to plow under. Possible other factors lending to their failure include inefficient storage of winter precipitation, late seeding, poor timing of plow down, and a lack of nodulation which continues to be a problem of dryland legume culture today, especially with small-seeded legumes. The above substantiate their conclusion that the main effect of the green manures was to reduce the water available to the ensuing grain crops. A re-examination of the Moccasin and Huntley, Montana data indicates that grain yields after green manures were slightly higher than grain yields after fallow for eight of the last ten years of the study.
826. Bezdicek, D. and R. Lockerman. no date. Crop rotation and the response of cereal crops to nitrogen in the PNW. unpublished.
Experiments conducted at Pullman, WA and Bozeman, MT. Year 1 - legumes (rainfall -Pullman 500 mm, Bozeman 480 mm). Year 2 -Pullman winter wheat + N (rainfall 350 mm); Bozeman barley + N (rainfall 200 mm). Compared fababean, pea, lentil, chickpea, fallow at both locations. Pullman legumes were used as green manure, Bozeman legumes were harvested for seed. N fertilizer equivalents ranged from 30-86 kg/ha N at Pullman (fallow = 125) and from 27-81 kg/ha N at Bozeman (fallow = 53). All cereals responded to added N, although less so at Pullman. More N was removed in seed than was fixed. Seed legumes appeared to fix 50-100 kg/ha N. The rotation effect was more significant at Pullman. T: cereal yields; fertilizer N equivalent; moisture depletion.