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The Nitrogen Nutrition of Soybeans: I. Effect of Inoculation and Nitrogen Fertilizer on the Yield and Composition of Beans on Marshall Silt Loam
Author(s) -
Norman A. G.
Publication year - 1944
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1944.036159950008000c0042x
Subject(s) - loam , nitrogen , fertilizer , yield (engineering) , mathematics , composition (language) , field experiment , inoculation , horticulture , agronomy , soil water , chemistry , environmental science , art , biology , statistics , physics , soil science , literature , organic chemistry , thermodynamics
T acreage of soybeans planted in Iowa and adjacent states has rapidly increased in the past few years, and this increase has brought into prominence a number of practical agronomic problems of some diversity. For example, there, is little information available as to the effects of this crop on soil fertility, and therefore the question of the proper place of this crop in the rotations suitable to the region is by no means settled. Conversely the effects of different levels of soil fertility on the soybean crop are not fully understood, with the result that questions of efficient land-use remain largely unanswered. It is a characteristic of the prairie-derived soils that the supply of available nitrogen therein is relatively high. The state-wide corn yield in Iowa in 1942 was over 60 bushels per acre. About 90 to 100 pounds of nitrogen is present in a corn crop of this magnitude. Soybeans in Iowa, though they may have, if nodulated, an accessory source of nitrogen, are therefore being grown on land much of which provides during the growing season 100 pounds or more of available nitrogen. A bean crop of about 20 bushels per acre contains approximately this amount of. nitrogen, and therefore it would seem that such yields could be obtained without fixation of additional amounts of nitrogen from the atmosphere. Most of the beans are, however, inoculated and become well nodulated, yet the state-wide average yield is .not in excess of 20 bushels per acre. The possibility arises that inoculated soybeans do not utilize as much of the available soil nitrogen as a nonlegume. This therefore calls for a field study of the effects of various levels of available nitrogen on the amount of nitrogen fixed by the soybean crop. The literature contains relatively few estimates of the amount of nitrogen fixed by soybeans, and on examination a number of these are found to be based on pot experiments multiplied up to an acre basis. Probably only one has been obtained from a replicated experiment of modern design. On Sassafras loam "in a relatively low state of fertility" Bear ( i ) 3 reported the apparent fixation of 56 and 38 pounds per acre, respectively, by two varieties of soybeans. Fred and Graul (4) on duplicate plots at the Marshfield Station, Wis., found differences of 24 to 38 pounds of nitrogen between inoculated and uninoculated soybeans with various rates of application of lime. Fred (3) obtained a gain in nitrogen of 57 pounds per acre as a result of inoculation of soybeans on a light sand, on which, however, the uninoculated crop was virtually a failure. In a study (2) of methods of inoculation of Manchu beans on a prairie soil, the largest difference found for inoculation was 26.5 pounds nitrogen per acre. These amounts are not large, but it has to be taken into account that the soybean plant has a relatively short season of growth that coincides with the period of maximum nitrate liberation in the soil. The main practical problem involved in this and subsequent papers is the determination of the amount of nitrogen fixed by the soybean plant under field conditions and the effect of the amount of combined nitrogen present on growth and fixation under both field and greenhouse conditions.