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Monday, September 24, 2018

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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.

8907. Bremer, E., R.J. Rennie, and D.A. Rennie. 1988. Dinitrogen fixation of lentil, field pea and fababean under dryland conditions.. Can. J. Soil Sci. 68:553-562.
N15 was used to study the N-fixation of several grain legumes in Saskatchewan, with all major soil zones represented. Indigenous rhizobia were incapable of supporting adequate levels of N2 fixation at most sites. Inoculation increased total dry matter, total N, and N2 fixation of all legume cultivars tested. Annual rates of N2 fixation were as high as 75, 105, and 160 kg N/ha for lentil, pea, and fababean, respectively on gray and gray-black soils in one year, but declined by an average of 5.3, 7.6, and 10.5 kg N/ha, repsectively, for every cm reduction in moisture use. Fababean fixed the most N under wetter conditions, while pea and lentil fixed the most under drought stress conditions. The amount of N fixed was not significantly correlated with soil nitrate levels in either year, perhaps due to the overriding effects of moisture. Estimates of the % plant N derived from atmospheric fixation ranged from 30-80%, with fababean generally the highest. The % from atmosphere was negatively correlated to soil nitrate for pea and lentil.

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