Nitrogen Fertilization in Establishing Forage Legumes1
- S. M. Hojjati,
- W. C. Templeton and
- T. H. Taylor2
Forage legumes play a special role in agriculture in that they fix N and serve as feedstuffs for livestock and poultry. Researchers do not agree, however, concerning need for fertilizer N in legume establishment. We studied the effects of N applied at and shortly after planting of legumes on growth and N fixation and compiled information on current recommendations of agricultural experiment stations in the United States on use of N with forage legumes.
Two greenhouse experiments were conducted. In the first, seed of red clover (Trifolium pratense L.) and bigflower vetch (Vicia grandiflora var. kitalbeliana W. Koch) were planted in sand and given Hoagland's solution at planting or 3 or 6 weeks post-planting to. furnish 28, 56, or 112 ppm N (N1, N2, N3). A comparable N-free solution (No) was included. In the second, red clover, vetch, and alfalfa (Medicago sativa L.) were seeded into three soils and fertilized with NaNO3 at rates to supply 30 or 60 kg N/ha, and a no-N check. Plants were harvested at 8 or 9 weeks post-planting, roots and tops separated, and N fixation estimated by C2H2 reduction. After drying, plant parts were weighed, ground, and analyzed for N. Published recommendations for fertilizing legumes were requested from Agronomy Departments in the United States, and these were summarized.
In trial 1 N1, N2, and N3 plants were larger than No plants but, at harvest, fertilized clover plants were fixing only 63, 33, and 6% as much N/pot/hour, respectively, as the latter. Interactions among treatment variables were common. In contrast, level of N applied in experiment 2 did not affect N fixation. Growth was increased equally by 80 and 60 kg N/ha.
Current recommendations concerning N usage on forage legumes vary widely, especially with grass-legume mixtures. The findings in these greenhouse experiments and the disparities in state recommendations indicate need for further research to more clearly define the conditions, if any, under which use of N with forage legumes is justified.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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