Browse on keywords: fertility nitrogen fixation
Search results on 05/24/13
690. Bear, F.E.. 1931. Soil management.. J. Wiley, N.Y..
A fairly complete text on soil management - fertility, tillage, organic matter, fertilizers; describes proper plow, moisture content, and depth to improve soil tilth; describes weeds as a potential cover crop; field study in England - free living N fixers input ~44 lb/ac/yr (est.). Azotobacter critical pH = 6.4.
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.
1558. Day, J.M., D. Harris, P.J. Dart and P. Van Berkum. 1975. The Broadbalk experiment: an investigation of nitrogen gains from non-symbiotic fixation. p. 71-84 IN:. W.P. Stewart (ed.), Nitrogen fixation by free living microorganisms, Cambridge Univ. Press.
4845. Newton, J.D.. 1954. Microbial maintenance of nitrogen in western Canada's grey wooded, black earth, and brown prairie soils.. Trans. 5th Intl. Congress of Soil Sci. Vol. 3:76-87.
Soil nitrate levels were higher for 3-4 years after alfalfa than after grass. Legumes responded to sulfur additions. Non-symbiotic N fixation was felt to account for significant N increases in lab studies with various soils. Maintenance of long-term yields was helped by heavy additions of straw.
7066. Vandecaveye, S.C. ad S. Anderson. 1934. Longevity of Azotobacter in soils treated with lime and superphosphate.. J. Am. Soc. Agron., 26:353-364.
Few Azotobacter in soils below pH 6.0, according to early studies; need several thousand colonies per gram of dry soil to get appreciable N fixation: liming increased Azotobacter in acid soils; phosphorus addition had no effect; large seasonal fluctuation in Azotobacter; highest numbers in spring and fall. T: Seasonal Azotobacter changes; effect of pH, lime, P.
7972. Sims, J.R., M.K. Muir, and A.E. Carleton. 1968. Evidence of ineffective Rhizobia and its relation to the nitrogen nutrition of sainfoin (Onobrychia viciaefolia).. IN: C.S. Cooper and A.E. Carleton (eds.). Sainfoin Symposium. MT Agr. Expt. Sta. Bull. 627.
10079. Cowie, A.L., R.S. Jessop, D.A. MacLeod and G.J. Davis. 1990. Effect of soil nitrate on the growth and nodulation of lupins (Lupinus angustifolius and L. albus).. Austral. J. Expt. Agric. 30:655-659..
The effect of increasing external nitrate concentration on the nodulation of Lupinus albus and L. angustifolius lines was examined in two sand culture experiments. In the first experiment four lines, three L. albus and one L. angustifolius, were grown at nitrate concentrations of 0, 2, 8, 16, and 30 mmol/L for 49 days. Increasing the nitrate concentration reduced nodule weight in all varieties to a similar extent. In a second experiment, 18 L. angustifolius lines were grown at nitrate concentrations of 2 and 8 mmol/L for 49 days. The ratio of nodule weights at the 8 and 2 mmol/L nitrate treatments varied widely, from 23 to 71%, between the lines. There appears to be potential for selection of L. angustifolius varieties able to maintain nitrogen fixation at increased levels of soil N.