INITIAL STUDIES ON SOIL NITROGEN MANAGEMENT, SOYBEAN NITROGEN RELATIONS,AND BEAN LEAF BEETLE BIOLOGY

Authors: Riedell, Walter; Lundgren, Jonathan; Osborne, Shannon; Pikul Jr, Joseph

Submitted to: Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 2/11/2006
Publication Date: 3/7/2006
Citation: Riedell, W.E., Lundgren, J.G., Osborne, S.L., Pikul Jr, J.L. 2006. Initial studies on soil nitrogen management, soybean nitrogen relations,and bean leaf beetle biology. In: A.J. Schlegel (ed.) Proc. Great Plains Soil Fertility Conference. Vol. II. March 2-3, 2006. Denver, CO.

Interpretive Summary: Economic thresholds for bean leaf beetle on soybean have been established on the basis of damage to above-ground parts of soybean plants. The economic importance of larval feeding on roots and nodules is not fully understood, although this kind of injury is likely to have a serious impact on yields. In the northern Great Plains, N starter fertilizer applied to soybeans planted in late May reduced ureide levels (ureides are indicators of N fixation through mid July. Because soybean root nodules are an important food source for bean leaf beetle larvae and because first generation adult beetles begin to emerge from soybean fields in mid-July (Catangui 2003), it is possible that soil management tactics that affect soybean nodulation, such as starter N application, could have an effect on bean leaf beetle biology. Our objective was to investigate the potential relationships between soil N management, soybean N relations, and bean leaf beetle biology. Our findings suggest that, because the soybean planting date was postponed 3 weeks due to inclement weather, the soil N management treatments imposed during the 2005 growing season had little effect upon ureide-N concentration. This suggests that there were few differences in soybean root nodulation and atmospheric N fixation across treatments. Thus it was not surprising to find that there were no major effects of soil N management treatments on bean leaf beetle larval populations. Additional data over multiple years are needed to properly test our hypothesis.

Technical Abstract: Bean leaf beetles (Cerotoma trifurcata) are serious insect pests of soybeans (Glycine max). This study was conducted to determine if soil nitrogen (N) input treatments would impact the biology of this emerging pest species. The experiment was conducted in the soybean phase of a long-term corn/soybean rotation study near Brookings SD. Soil N input treatments were: corn fertilized for a yield goal of 8.5 Mg ha-1 (high N input), 5.3 Mg ha-1 (medium N input), or corn not fertilized (no N input). Corn and soybean plots also were treated with banded starter fertilizer (112 kg ha-1) as 14-16-11, 7-16-11, or 0-16-11 elemental N-P-K on the high N, medium N, and no N input treatments, respectively. Soybeans grown on high N input plots showed similar shoot ureide-N concentrations at all development stages studied. Bean leaf beetle larvae were present in the soil from just prior to the beginning flowering stage until the beginning maturity stage (about 65 days). There were no consistent N input treatment effects observed in the cumulative number of larvae found in the plots. Our findings suggest that the soil N management treatments imposed during the 2005 growing season had little effect upon ureide-N concentration, which in turn suggests that there were few differences in soybean root nodulation and atmospheric N fixation across treatments. Thus it was not surprising to find that there were no major effects of soil N management treatments on bean leaf beetle larval populations