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ARS Home » Plains Area » Brookings, South Dakota » Integrated Cropping Systems Research » Research » Publications at this Location » Publication #220084
Title: Impact of low rates of nitrogen applied at planting on soybean nitrogen fixation

Author
item Osborne, Shannon
item Riedell, Walter

Submitted to: Journal of Plant Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/6/2010
Publication Date: 1/18/2011
Citation: Osborne, S.L., Riedell, W.E. 2011. Season impact of low rates of nitrogen applied at planting on soybean nitrogen fixation. Journal of Plant Nutrition. 34:436-448.

Interpretive Summary: Soil conditions at planting in the northern Great Plains can delay emergence, nitrogen fixation and growth of soybean. Fertilizer nitrogen applied at planting may increase initial growth of soybean. The objective of this study was to evaluate the impact of low rates of nitrogen applied at planting on soybean nitrogen fixation and growth. A field experiment was established within a 2-yr corn soybean rotation. Experimental tillage treatments were no-tillage (NT) and conventional tillage (CT). Starter nitrogen treatments were two different nitrogen sources ammonium nitrate (AN) or urea (UR) each applied at 0, 7, 14, and 21 lb/ac. Early growth was stimulated by application of nitrogen with biomass increasing as nitrogen rate increased. The amount of nitrogen fixation increased with growth stage reaching a maximum fixation at the R5 growth stages. Plant ureide content (an estimate of N fixation) decrease with increase nitrogen applied for all growth stages except R7. Nitrogen applied at planting reduced early season nitrogen fixation, but increased biomass production. At later growth stages, impact of nitrogen fertilization on ureide content decreased. The increase in plant biomass contributed to an overall increase in yield indicating that in unfavorable environments application of nitrogen at planting can have a positive impact on soybean growth.

Technical Abstract: Environmental conditions in the northern Great Plains can delay emergence, nitrogen (N) fixation and growth of soybean [Glycine max (L.) Merrill] due to cool and wet soil conditions at planting. Fertilizer N applied at planting may increase initial growth of soybean. The objective of this study was to evaluate the impact of low rates of N applied at planting on soybean N fixation and crop growth. A field experiment was established within a 2-yr corn [Zea mays (L.)] soybean rotation using a split-plot design with four replications. Whole plots were no-tillage (NT) and conventional tillage (CT) and the split plots were starter fertilizer (two sources x four rates) treatments. Nitrogen sources were either ammonium nitrate (AN) or urea (UR) each applied at 0, 8, 16, and 24 kg N ha-1. Early growth was stimulated by application of N with biomass increasing as N rate increased. The amount of plant N fixation increased with growth stage reaching a maximum fixation at the R5 growth stages. Plant ureide content (an estimate of N fixation) decrease with increase N applied for all growth stages except R7. Nitrogen applied at planting reduced early season N fixation, but increased biomass production. At later growth stages, impact of N fertilization on ureide content decreased. The increase in plant biomass contributed to an overall increase in yield indicating that in unfavorable environments application of N at planting can have a positive impact on soybean growth.