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Title: CONTRIBUTION OF AMMONIUM TO STIMULATION OF SMOOTH PIGWEED (AMARANTHUS HYBRIDUS L.) GERMINATION BY EXTRACTS OF HAIRY VETCH (VICIA VILLOSA ROTH) RESIDUE

Author
item Teasdale, John
item Pillai, P

Submitted to: Weed Biology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/2/2004
Publication Date: 1/1/2005
Citation: Teasdale, J.R., Pillai, P. 2005. Contribution of ammonium to stimulation of smooth pigweed (Amaranthus hybridus L.) germination by extracts of hairy vetch (Vicia villosa Roth) residue. Weed Biology and Management. 5:19-25.

Interpretive Summary: Hairy vetch is a popular cover crop that provides many benefits including improving soil nutrition, quality, and water infiltration and retention. Residue of hairy vetch on the surface of soils can suppress weeds, but at lower levels can intermittently stimulate emergence of weeds, particularly the common annual weed, smooth pigweed. This research was conducted to understand the nature of this stimulation phenomenon. Results demonstrated that ammonium released from hairy vetch residue explains the stimulation of pigweed germination. It also can explain the intermittent nature of this stimulation since it is expressed most prominently only with dormant seed, under conditions of light and intermediate temperatures, and with intermediate concentrations of ammonium. This research will be useful to researchers interested in understanding the complex interactions between residue on the soil surface and behavior of weed and pest organisms in the soil.

Technical Abstract: Hairy vetch is a leguminous winter annual cover crop that contributes toward meeting the nitrogen requirement of succeeding crops. Hairy vetch residue is capable of suppressing weeds but low levels of residue have been shown to intermittently stimulate emergence of weeds, particularly smooth pigweed. This research was conducted to assess the inhibitory and stimulatory effects of hairy vetch extracts on two smooth pigweed lots with differing dormancy conditions under differing germination conditions (25 or 35 C in light or dark). Full strength extracts inhibited germination of both lots under all conditions, a result explained by an inhibitory osmotic potential of the full strength extract. At 0.1X and lower dilutions of hairy vetch extract, there was a slight stimulation of germination above that of the control (average of 11%) of both lots of pigweed under all germination conditions except for a large stimulation (87%) by the more dormant lot at 25 C in light. A similar response to ammonium hydroxide solutions was observed in which germination stimulation averaged 7% for all conditions except for germination of the dormant pigweed lot that was stimulated 115% by 15 ppm of ammonia species (primarily ammonium ions) at 25 C in light. Since the ammonium concentration in the hairy vetch extract (16.9 ppm) was similar to that in the ammonium hydroxide solutions that promoted the largest stimulation of germination, and since there was a high correlation (r=0.978) between the degree of germination stimulation by hairy vetch extracts and by ammonium hydroxide, ammonium appears to be the principle ingredient in the extract responsible for stimulation of smooth pigweed germination.