Submitted to: Weed Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/17/2010
Publication Date: 4/1/2011
Publication URL: http://naldc.nal.usda.gov/catalog/49543
Citation: Wortman, S., Davis, A.S., Schutte, B.J., Lindquist, J. 2011. Integrating management of soil nitrogen and weeds. Weed Science. 59(2):162-170. Interpretive Summary: Designing weed suppressive agroecosystems is a central goal of integrated weed management. Controlled-environment studies have demonstrated that soil nitrogen fertility may be managed to benefit crop growth more than that of competing weeds, however literature reports of the efficacy of integrated crop, soil and weed management are highly variable. Our aim was to discriminate between soils that are amenable to this management approach and those that are not. We hypothesized that soils with high background levels of nitrogen fertility would not show an influence of nitrogen fertilization level on weed-crop interference, whereas those soils with low background nitrogen levels would show a response of weed-crop interference to soil nitrogen fertilization level. This hypothesis was supported by experimental results under greenhouse conditions. However, field experiments in both Urbana, IL, and Lincoln, NE, did not support this hypothesis, showing lowest corn yield loss under nitrogen fertilization levels targeted to maximize corn yield, independent of weed management concerns. Although our study sites had low background soil nitrogen levels in relation to neighboring fields, all sites had deep, prairie-derived soils, and none were strongly nitrogen limited. In contrast, literature reports of successful integration of soil nitrogen and weed management were conducted primarily on shallow, low-fertility soils.
Technical Abstract: Crop-weed interference often depends on soil nitrogen (N) supply and the N mineralization potential of the soil. Knowledge of these soil properties combined with an understanding of weed-crop competition dynamics in response to soil nutrient levels can be used to optimize N fertilizer rates to shift the competitive advantage to crop species. A greenhouse study (2006) and field studies (2007-2008) in Illinois and Nebraska were initiated to quantify the growth and interference of maize and velvetleaf in response to varying synthetic N fertilization rates in soils with high and low N mineralization potential. Typically, soils with <150 ppm amino sugar N were classified as responsive (R) to synthetic N fertilization, while soils with >280 ppm amino sugar N were classified as nonresponsive (NR) to synthetic N fertilization. We set out to create NR soil by amending local soils with composted manure to raise amino sugar N levels. Maize and velvetleaf were grown in monoculture or in mixture in the NR and R soils fertilized with zero, medium or full locally recommended N rate. As N rate increased in the NR soil (over-fertilization) in the greenhouse, maize biomass reduction tended to increase, but as N rate increased in the R soil, biomass reduction tended to decrease. In contrast, maize vegetative biomass reduction and grain yield loss were unaffected by the interaction of soil class and N rate in the field. In both greenhouse and field experiments, velvetleaf biomass was greater in the NR soil class and biomass reduction was generally greatest in the R soil class. This demonstrates the competitive advantage of weedy species in nutrient-rich soils. While soil N levels influenced weed-crop interference in the greenhouse, the results of the field study demonstrate the difficulty of controlling soil nutrient dynamics in the field.