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Nitrogen fixation in high yielding soybean (Glycine max., L. Merr)

Fernando Salvagiotti, University of Nebraska - Lincoln


Under the hypothesis that grain yield is limited by nitrogen (N) supply in late reproductive stages when soybean is grown in high-yielding environments, a 2-year study was conducted in order to evaluate whether N fertilization increases grain yield and N uptake, and to what extent N2 fixation is complemented when fertilizer N was applied both on surface as well as below the nodules. Four N fertilization treatments were established in the soybean main plots of each year's soybean/maize rotation in a long-term experiment. Treatments were: a non-fertilized plot (N1) and 180 kg N ha-1 applied as (i) polymer-coated controlled release urea placed 20 cm below the surface before planting (N2, late N fertilization strategy); (ii) ammonium nitrate on the surface before planting and at V6 (N3, early N fertilization strategy) and, (iii) ammonium nitrate on the surface at R5 (N4, late N fertilization strategy). All treatments were superimposed on two contrasting fertilizer management histories for maize (M1=recommended nutrient management; M2=intensive nutrient management). Grain yield in N1 averaged 4850 kg ha-1, and a 5% increase was observed in response to N fertilization. This response was accompanied by a 9% increase in N uptake. Biological N2 fixation accounted for 50% of N uptake in N1, but only 32 and 38% in N3 and N4, respectively. All N fertilization strategies succeeded in providing the additional N needed to attain the apparent maximum grain yield, but the amount of fertilizer N needed to achieve grain yield response was larger with ammonium nitrate applied on the surface N. This was because a proportion of total N derived from surface applied ammonium nitrate depressed N2 fixation. In contrast, deep placement of slow-release urea did not depress biological N2 fixation, and thus, showed the advantage of providing the additional N needed to reach grain yield potential with minimal trade-off between fixed N and fertilizer N. The greater photosynthesis response to light observed in fertilized soybean suggests that N fertilization in high-yielding soybean should simultaneously take into account management practices intended to maximize canopy light capture. ^

Subject Area

Agriculture, Agronomy|Agriculture, Soil Science

Recommended Citation

Salvagiotti, Fernando, "Nitrogen fixation in high yielding soybean (Glycine max., L. Merr)" (2008). ETD collection for University of Nebraska - Lincoln. AAI3315056.