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ARS Home » Plains Area » Brookings, South Dakota » Integrated Cropping Systems Research » Research » Publications at this Location » Publication #160706
Title: IMPACT OF STARTER NITROGEN FERTILIZER ON SOYBEAN NITROGEN FIXATION

Author
item Osborne, Shannon
item Riedell, Walter

Submitted to: Soil/Water Research, Progress Report
Publication Type: Experiment Station
Publication Acceptance Date: 3/1/2004
Publication Date: 3/25/2004
Citation: Osborne, S.L., Riedell, W.E. 2004. Impact of starter nitrogen fertilizer on soybean nitrogen fixation. 2003 Progress Report #SOIL PR 03-38. Agricultural Experiment Station, Plant Science, South Dakota State University. Brookings, SD.

Interpretive Summary: Environmental conditions at the time soybeans (Glycine max (L.) Merrill) are planted in the northern Great Plains are such that nitrogen (N) fixation may not occur immediately, therefore additions of N as starter fertilizer may increase initial growth of soybeans and possibly increase yield and quality. The objective of this study was to evaluate the response of soybeans to low rates of N applied at planting. A field experiment was established within a two-year corn (Zea mays L.) soybean rotation using a split-plot design with four replications. Whole plots were no-till (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. Plant ureide concentration was significantly higher for UR compared to AN for the R1 sampling date for 2000 and 2002 with no response in 2001, possibly due to differences in planting dates. Tillage significantly affected ureide concentration at the R7 growth stage 2001 and 2002, with the NT treatments resulting in a higher ureide concentration compared to CT. Relative ureide content decreased with increasing N rate for the R1 sampling date in all years. This decrease in N fixation was not present for the R7 sampling date but the significant increase in biomass production was still present, possibly indicating the potential benefits of applying N fertilizer at planting in unfavorable environmental conditions.

Technical Abstract: Environmental conditions at the time soybeans are planted in the northern Great Plains are such that nitrogen fixation may not occur immediately; therefore additions of nitrogen as starter fertilizer may increase initial growth of soybeans and possibly increase yield and quality. The objective of this study was to evaluate the response of soybeans to low rates of nitrogen applied at planting. A field experiment was established within a two-year corn/soybean rotation. Treatments included no-till, conventional tillage and starter fertilizer. Nitrogen fertilizer was applied as either ammonium nitrate or urea each at rates of 0, 7, 14, and 21 lb/ac. Plant ureide concentration was significantly higher for urea compared to ammonium nitrate for the beginning bloom sampling date for 2000 and 2002 with no response in 2001, possibly due to differences in planting dates. Tillage significantly affected ureide concentration at the beginning maturity growth stage 2001 and 2002, with the no-till treatments resulting in a higher ureide concentration compared to conventional tillage. Relative ureide content decreased with increasing nitrogen rate for the beginning bloom sampling date in all years. This decrease in nitrogen fixation was not present for the beginning maturity sampling date but the significant increase in biomass production was still present, possibly indicating the potential benefits of applying nitrogen fertilizer at planting in unfavorable environmental conditions.