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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.
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.
8735. Haimanot, K.. 1977. Long-term effects of crop and soil management practices on crop yield and soil chemical composition.. M.S. Thesis, Dept. of Agronomy and Soils, Washington, ST. Univ., Pullman, WA 99164-6420.
The study site was located near Dusty, WA in the intermediate rainfall zone. Cropping system treatments were run from 1952 to 1970. Thirteen different cropping systems with three N fertilizer levels were used, including continuous cropping, green manures, and fallow systems. Wheat yields in rotation using 30 lb N/ac were higher than yields in an alfalfa rotation. Wheat yields were higher after Austrian winter pea green manure than after alfalfa or sweetclover. Per acre per year crop yields were highest for fertilized, continuous cropping. Soil pH increased with sweetclover GM and decreased with N fertilizer added. Significant increases in soil organic matter occurred in rotations with alfalfa (+0.08%), on winter wheat - fallow (+0.30%), and with winter wheat - spring wheat - fallow with N (+0.26%).
10475. Campbell, C.A., G.P. LaFond, A.J. Leyshon, R.P. Zentner, and H.H. Janzen. 1991. Effect of cropping practices on the initial potential rate of N mineralization in a thin Black Chernozem.. Can. J. Soil Sci 71:43-53.
Potentially mineralizable N (No) was examined as a possible indicator of soil organic matter change due to management, using soil from 30 yr rotation plots near Indianhead, Saskatchewan. A parameter called the initial potential rate of N mineralization (No x rate constant k at time =0) was effective in distinguishing both the absolute and qualitative changes in soil organic N due to various management practices. The results showed that fertilizers can be as effective as legumes, used either for green manure or hay, in increasing the quantity and improving the quality of soil organic matter. Organic matter changes were similar between a 6 yr soil-building rotation and fertilized continuous wheat, but higher than unfertilized continuous 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.