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Research Project: DEVELOPMENT OF MULTI-TACTIC WEED MANAGEMENT SYSTEMS FOR SUSTAINABLE CROP PRODUCTION

Location: Sustainable Agricultural Systems Laboratory

Title: Nitrogen competition between corn and weeds in soils under organic and conventional management

Author
item Poffenbarger, Hanna
item Mirsky, Steven
item Teasdale, John
item Spargo, John - Pennsylvania State University
item Cavigelli, Michel
item Kramer, Matthew

Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/21/2014
Publication Date: 4/1/2015
Citation: Poffenbarger, H.J., Mirsky, S.B., Teasdale, J.R., Spargo, J.T., Cavigelli, M.A., Kramer, M.H. 2015. Nitrogen competition between corn and weeds in soils under organic and conventional management. Weed Science. 63(2):461-476.

Interpretive Summary: Cropping systems research has shown that organic systems can have comparable yields to conventional systems at higher weed biomass levels. Higher weed tolerance in organic systems could be due to differences in long-term soil fertility management. The objective of our study was to test whether inherent soil N mineralization differences in organic and conventionally-managed soils from a long-term cropping systems experiment resulted in different early-season weed-crop competition relationships. Over time, corn was a much better competitor for soil inorganic nitrogen than weeds. However, differences were not observed between organic and conventional soils when weeds and corn were grown in mixture. Therefore, at least during the early phase of competition, differences in soil fertility conditions in long-term organic and conventional management do not appear to influence weed-crop competition. This work eliminates potential factors that may contribute to weed tolerance in organic systems and will be used by researchers to inform future experiments from a methodological standpoint. Furthermore, this underscores, to growers, the importance of optimizing corn establishment and early growth conditions to compete effectively against weeds in organic systems.

Technical Abstract: Cropping systems research has shown that organic systems can have comparable yields to conventional systems at higher weed biomass levels. Higher weed tolerance in organic systems could be due to differences in labile soil organic matter and nitrogen (N) mineralization potential. The objective of our study was to test whether inherent soil N mineralization differences in organic and conventionally-managed soils from a long-term cropping systems experiment resulted in different early-season weed-crop competition relationships. A greenhouse experiment was conducted using corn (Zea mays L.), smooth pigweed (Amaranthus hybridus L.) and giant foxtail (Setaria faberi L.) grown in crop/weed mixtures of 100/0, 75/25, 50/50, 25/75 and 0/100 and harvested at 24, 35 and 43 days after planting. Averaged across species, the monocultures grown in soil under organic management had significantly higher shoot N content at the two later harvest dates (p<0.05). Competition over N was not apparent at the first harvest date, but corn was more competitive than both weed species at the later harvests. We found little evidence of resource partitioning when the mixtures were N-limited. The results indicate that greater weed tolerance in organic systems is not likely due to differences in soil mineralizable N.