Inoculant Impacts on Organic Vegetable Production in the Upper Great Plains

Final Report June 2019

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Principal Investigators:

Greta G. Gramig, Associate Professor , Department of Plant Sciences, North Dakota State University, P.O. Box 6050, Department 7670, Fargo, ND 58102-6050

Patrick M. Carr, Graduate Research Assistant, Department of Plant Sciences, North Dakota State University

Kenneth Paul Beamer, Associate Professor, Central Agricultural Research Center, Montana State University, 52583 US Highway 87, Moccasin, MT 59462-9512

Project Abstract

In the Northern Great Plains, adoption of roller-crimping for weed suppression in no-till organic cropping systems remains a challenge due to limited growing season and delayed soil warming, which limit production of sufficient cover crop biomass to suppress weeds. A solution may be to grow weed-suppressive biomass out of phase spatially and temporally with the main crop, an approach called ‘deep mulching.’ Field experiments were conducted at two sites in North Dakota to investigate effects of no-till deep mulch compared to tillage on soil quality indices, weed densities, and weed seedbank densities. We hypothesized that employing no-till deep mulch and arbuscular mycorrhizal fungi (AMF) inoculant would be associated with reductions in realized weed and weed seedbank densities, time required for hand weeding, as well as with improvements in soil quality and vegetable yield. No-till deep mulch treatments were associated with reductions in weed seedbank density and realized weed density compared to tilled treatments, reductions in weeding time, improvements in soil quality indices (e.g., aggregate stability and soil respiration), increased soil N and P, and greater AMF biomass. No-till deep mulch treatments were consistently associated with greater vegetable crop yield compared to tillage. AMF inoculant did not affect realized weed or seedbank density, soil quality, or vegetable yield. Our findings suggest no-till deep mulch (especially using alfalfa hay as a mulch) may be a viable option for small scale organic vegetable producers in the Northern Great Plains to improve or maintain soil quality, increase crop yield, as well as reduce weed densities, weed seedbank densities, and time required for weeding. Additional economic research is needed to determine costs associated with sowing, harvesting, baling, and applying alfalfa mulch compared to tilling.


Two overall objectives were addressed by this research project:

  1. Investigate the utility of a ‘deep mulch’ system for weed suppression in various organically produced vegetable crops.
  2. Evaluate the efficacy of a commercially available AMF (arbuscular mycorrhizal fungi) inoculant for enhancing crop yield and nutrient uptake.

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