Monday, November 13, 2006

A Comparison of Organic Matter and Elemental Allelopathy in Determining Sustainable Grass Ecosystems.

Rick Bottoms1, C. J. Nelson2, and John Coutts2. (1) Univ of CA, Desert Res & Ext Center, 1004 E Holton Rd, El Centro, CA 92243, (2) Agronomy Dept, 210 Waters, Univ of Missouri, Columbia, MO 65211

An extensive field study of the invasive properties of Russian knapweed (Acroptilon repens) at three locations in New Mexico were compared to earlier published results depicting interference mechanisms that contribute to their robustness. Long term evaluations determined elemental allelopathy properties to be present in arid Wyoming ecosystems. We noted organic matter and soil Zn at 0-1.25-cm depth in knapweed infested areas was 9 to 10-fold greater, nearly double the 0-2.5-cm depth and at 7.5-15 cm depth was 3 to 5-fold greater than in non-infested areas of native grasses. Accumulated plant duff and organic matter and soil nutrient values indicate over 40 years was necessary to develop an invasive monoculture yielding 2526 kg ha of knapweed compared to 322, and 863 kg ha for, native grass and plantings of Bozoisky Russian wildrye (Psathyrostachys juncea Fisch. Nevski), respectively. Similar studies from New Mexico indicate the same interference mechanisms and trends may be present in invaded arid landscapes. A composite snapshot of organic matter levels depicts a 2X increase under knapweed infested sites from three 10-15 year old locations as compared to native vegetation sites. Accumulated Zn was found to have a 4X increase at the same sites. Research assessments indicate accumulated plant duff and organic matter levels indicate it could take 200 or more years to return the soil profile to its native state. Our findings of 10 year comparisons indicate soil, tissue and duff nutrient values from pre-invasion nutrient levels can be realized 14 to 38 years following renovation treatments that suppress elemental allelopathy influences from invasive Russian knapweed.