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1015. Bowren, K.E. (ed.).. 1986. Soil improvement with legumes.. Saskatchewan Agriculture, Soils and Crops Branch.
This excellent publication summarizes research over the past 40 years pertaining to the use of legumes for soil improvement in Saskatchewan. The role of legumes in maintaining soil nitrogen was crucial prior to available fertilizer. But their value extends beyond their nitrogen contribution to the improvement of soil physical properties. One study found the tillage draft requirement to be up to one-third lower where legumes had been a regular part of the rotation. The positive effects of alfalfa were measured for over ten years in a series of wheat crops compared to plots with no alfalfa. Over 17 years, the average grain yield from a wheat-wheat/clover-clover green manure rotation with no fertilizer were 30% higher that a wheat-wheat-fallow rotation with fertilizer. Moisture depletion by legumes is the biggest hurdle to their use in very dry areas. Adequate fertility for the legumes is necessary to maximize their benefit. Use of selected Rhizobium strains can improve nitrogen fixation, especially on acid soils. Several varieties of sweetclover are mentioned with adaptation to forage or green manure use. The booklet has numerous color photos and many data tables and figures.
2784. Hulbert, H.W.. 1927. Sweetclover.. ID Agr. Expt. Sta. Bull. #147.
Biennial white is best forage, biennial yellow is too short; can handle alkaline soils; earlier seeding is best; 15 lb/ac seed, or 10 lb/ac in drier areas; nurse crop is risky, peas may be best; 3/4 T/ac hay first season, 2-3 T/ac second year; best used for pasture and soil improvement; can be grazed early spring through fall; improves soil quality, breaks up subsoil; sweetclover as green manure too expensive for dry areas; one system used is WW/SC planted in fall (unscarified seed) at 5 lb/ac; after wheat harvest, pastured SC into late fall; field is spring plowed and SF; then WW again, this raised WW yields 3-8 bu/ac; might try with Hubam (annual) SC.
4377. McKay, H.C. and W.A. Moss. 1949. High protein wheat with conservation farming.. U. of Idaho Extension Bull. #181.
Emphasize need for legume - grass rotation to maintain soil productivity. Suggest a 7 yr sweet clover rotation or a 9 yr alfalfa rotation. Yellow sweet clover plus mountain bromegrass or slender wheatgrass; Ladak alfalfa plus smooth brome and big bluegrass (high rainfall) or crested wheatgrass (low rainfall); early spring seeding recommended without nurse crop; methods of establishment, plow sweetclover at 12-22" height; use sweetclover as a surface mulch to prevent erosion. T: soil moisture and sweetclover growth; wheat after sweetclover; yield and protein.
5705. Rasmussen, P.E., H.P. Collins, and R.W. Smiley. 1989. Long-term management effects on soil productivity and crop yield in semi-arid regions of eastern Oregon.. OR Agr. Expt. Sta. Bulletin 675.
Summary of over 50 years of plot research at Pendleton, OR, with some results from Weston and Moro. Focuses on results from a continuous set of plots at the Pendleton station. Manure maintained highest yields, highest soil organic matter, highest pH compared to other treatments. Nitrogen fertilizer had a more marked effect on water infiltration than various tillage treatments. Green manure systems are generally not economic in the drier areas, due to competition for moisture with wheat, which is the most profitable crop. Legumes can contribute between 40 and 80 lb/ac N to the following crop. Varietal improvement over the past 50 years has been the most significant factor in increasing wheat yields. Burning straw accelerated organic matter losses from the soil and eventually reduced yields. Marginal returns have generally been lower from alternative crops than from wheat.
10576. Janzen, H.H. and G.D. Radder. 1989. Nitrogen mineralization in a green manure amended soil as influenced by cropping history and subsequent crop.. Plant Soil 120:125-131.
In a greenhouse study, surface soil from long-term experimental spring wheat rotations was amended with 15N labelled legume green manure and subsequently cropped (canola and spring wheat) or incubated. N mineralization from both the indigenous soil N and from green manure was suppressed in cropped soil. Net N mineralization in the uncropped and cropped treatments averaged 73 and 43 mg/kg, respectively. This difference was attributed in part to enhanced biological immobilization in the rhizosphere. These data suggest that short-term N mineralization is favored by fallowing soil after green manure application whereas N retention in organic matter is favored by immediate cropping.