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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.
1180. Campbell, C.A., R.P. Zentner and P.J. Johnson. 1988. Effect of crop rotation and fertilization on the quantitative relationship between spring wheat yields, available soil moisture, and precipitation.. Canadian J. Soil Sci., 68(1):1-16.
The effects of crop rotation and fertilization on the quantitative relationship between spring wheat yields, available soil moisture, and growing season precipitation were determined. Stubble-seeded wheat required 68 mm of moisture to produce the first kilogram per hectare of grain; fallow-seeded wheat required about 46mm. The lower threshold level of MU for grain production decreased from about 140mm to the values cited above; this has resulted in substantially greater moisture use efficiency in recent years likely due to better, more timely crop mangement and the improved cereal varieties.
1566. Derco, M. and V. Barta. 1983. The effect of organic fertilizers on the yield of short-term continually grown winter wheat in relation to soil water regime.. Rostlina Vyroba, 29(3), p.245.
Fertilizers were of little importance for the immediate increase in the grain yield; however, they might be significant from the viewpoint of the long-term effect on the soil fertility. The more effective measure appeared to be the choice of proper cultivar.
4807. Nelson, A.L.. 1950. Methods of tillage for winter wheat.. WY Agr. Expt. Sta. Bulletin 300.
Fallow/winter wheat production decreased soil N by 33% in the top 6" over 35 years. Continuous cropping lost 24% of the soil N. Crop rotations using green manure every 4th year did not decrease the loss of soil N. Average winter wheat yields (bu/ac) over 34 years for 3 rotations were: oats/rye(GM)/winter wheat/corn - 12.9; oats/peas(GM)/winter wheat/corn - 12.7; fallow/winter wheat - 13.7; oats/corn/winter wheat/rye - 13.2; oats/corn/winter wheat/peas - 14.1; oats/corn/winter wheat/fallow - 13.2. It was observed that green manure took years to break down. Tillage with an eccentric one-way increased winter wheat yields 2 bu/ac over 10 years compared to plowing. The eccentric one-way conserved moisture. Continuous cropping resulted in winter wheat yields 55% of biennial yields following fallow. Soil moisture was 3-4% lower in October after continuous cropping versus fallow.