Author
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Osborne, Shannon |
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Riedell, Walter |
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Submitted to: Journal of Plant Nutrition
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 11/1/2005 Publication Date: 5/8/2006 Citation: Osborne, S.L., Riedell, W.E. 2006. Soybean growth response to low rates of nitrogen applied at planting in the northern great plains. Journal of Plant Nutrition. 29:985-1002. Interpretive Summary: Cool and wet soils at the time of soybean planting in the northern Great Plains may reduce early crop growth and retard nitrogen fixation. Application of nitrogen as starter fertilizer may increase initial growth of soybean but may also negatively impact nitrogen fixation when environmental conditions improve. The objective of this study was to evaluate low rates of nitrogen applied at planting on soybean plant biomass production, nitrogen concentration, and estimates of nitrogen fixation under contrasting nitrogen sources and soil management practices in the northern Great Plains. A field experiment was established within a two-year corn soybean rotation. Treatments consisted of tillage and starter fertilizer (nitrogen source by rate). Nitrogen was applied in a 2 x 2 band at planting as either ammonium nitrate or urea, at four rates (0, 7, 14, and 21 lb N/ac). Biomass production significantly increased with increasing nitrogen rate for all growth stages. Plant ureide concentration was significantly greater for urea compared to ammonium nitrate for the R1 sampling date for 2000 and 2002 with no response in 2001, possibly due to later planting dates and warmer soil temperature. Ureide concentration and relative ureide decreased with increasing nitrogen rate for the R1 sampling date in all years indicating a decrease in nitrogen fixation up to that point in crop development. This decrease in nitrogen fixation was not present for the R7 sampling dates but the significant increase in plant growth was still present, indicating the possible importance of starter fertilizer in the cool environmental conditions of the northern Great Plains. Technical Abstract: Cool and wet soils at the time of soybean [Glycine max (L.) Merrill] planting in the northern Great Plains may reduce early crop growth and retard nitrogen (N) fixation. Application of N as starter fertilizer may increase initial growth of soybean but may also negatively impact N fixation when environmental conditions improve. The objective of this study was to evaluate low rates of N applied at planting on soybean plant biomass production, N concentration, and estimates of N fixation under contrasting N sources and soil management practices in the northern Great Plains. A field experiment (2000 to 2002) was established within a 2-yr 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. Biomass production significantly increased with increasing N rate for all growth stages and years except for the R7 sampling in 2002. Plant ureide concentration was significantly greater for UR compared to AN for the R1 sampling date for 2000 and 2002 with no response in 2001, possibly due to later planting dates and warmer soil temperature. Tillage significantly affected ureide concentration at the R7 growth stage 2001 and 2002, with the NT treatments higher than CT. Ureide concentration and relative ureide decreased with increasing N rate for the R1 sampling date in all years indicating a decrease in N fixation up to that point in crop development. Plant nitrate concentration increased with increasing N rate. This decrease in N fixation was not present for the R7 sampling dates but the significant increase in plant growth was still present, indicating the possible importance of starter fertilizer in the cool environmental conditions of the northern Great Plains. |
