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Title: CORN-WEED COMPETITIVE EFFECTS ON SOIL WATER DYNAMICS AND NUTRIENT UPTAKE

Author
item Teasdale, John
item Starr, James
item Sadeghi, Ali
item Rowland, Randy

Submitted to: Proceedings of Northeastern Weed Science Society
Publication Type: Abstract Only
Publication Acceptance Date: 10/28/2004
Publication Date: 1/3/2005
Citation: Teasdale, J.R., Starr, J.L., Sadeghi, A.M., Rowland, R.A. 2005. Corn-weed competitive effects on soil water dynamics and nutrient uptake [abstract]. Proceedings of Northeastern Weed Science Society. 59:12.

Interpretive Summary:

Technical Abstract: Weed competition for soil water and its resultant impact on corn (Zea mays L.) growth has not been well documented. This research was conducted in continuous no-tillage corn to assess the impact of cover-crop residue (plus or minus hairy vetch) and weed competition (plus or minus weeds) on water use and crop growth over two growing seasons. Treatment impacts were studied in 32 one-m2 sampling areas within replicated field plots during each of two droughty years. Soil water content was continuously monitored at 10-min intervals using multisensor capacitance probes located at the center of each sampling area. Probes were installed after corn emergence in the spring to monitor moisture centered at soil depths of 10-, 20-, 30-cm, and 40- or 50-cm. Vegetative biomass and nutrient content of weeds and corn was obtained for each sampling area at physiological maturity. Grain yield is not reported since grain fill was limited and erratic during these extremely dry seasons. Total biomass (corn plus weeds) was higher by 9% in 1998 and by 12% in 1999 in weedy versus weed-free corn. Water use (evapotranspiration) was determined for the period following each rainfall event and was found to be higher in weedy than in weed-free corn, particularly early in the season. The increase in water use in weedy corn following early rain events in each year can be attributed to use of 'free' water that was available early in the season before corn could access it. Corn was probably slower than weeds accessing this early water because there were 6 corn plants per m2 compared to 39 to 70 weed plants per m2, primarily fall panicum (Panicum dichotomiflorum Michx.) This free water accessed by weeds represented 28% in 1998 and 15% in 1999 of the total water used in weedy corn plots. Access to this early water by weeds may account for the higher total biomass achieved in weedy versus weed-free plots. Although total biomass and water use was not affected by cover crop, the distribution of biomass among species was affected by cover crop. Corn biomass was similar in treatments with or without hairy vetch in the absence of weeds, but corn biomass was higher with than without a hairy vetch cover crop in the presence of weeds. Weed biomass and population showed an opposite response, lower levels were observed with than without hairy vetch. Analysis of covariance confirmed that there was a negative linear relationship between corn and weed biomass. There was no interaction between cover crop and weed biomass indicating that the slope of corn biomass loss per unit weed biomass was similar regardless of cover crop. These results demonstrated that the competitive relation between corn and weeds was unaffected by cover crop and that the observed corn differences due to cover crop could be explained entirely by the presence of fewer weeds and lower biomass with than without hairy vetch.