Richard C. Rosecrance

REAL-TIME SOIL PROFILE WATER CONTENT AS INFLUENCED BY WEED-CORN COMPETITION

Weeds compete with crops for belowground resources; however, there is little detailed information on relative dynamics of soil water during competitive interactions. This research was conducted to determine changes in soil-water storage (CSWS) in rain-fed no-tillage corn (Zea mays L.) production in the presence or absence of weed competition over two droughty growing seasons. Weeds at the experimental site were composed primarily of fall panicum (Panicum dichotomiflorum Michx.), which represented >90% of plants present in both years. Corn-row soil-water infiltration and losses as CSWS were studied with multisensory capacitance probes that determined water status at depths of 5-15, 15-25, 25-35, and 35-45 cm on 10-min intervals. Total biomass (corn plus weed) was higher in weedy plots than in weed-free plots. Compared with weed-free plots, corn biomass was reduced by 28% in 1998 and by 21% in 1999 by weeds; a decrease defined by the same linear rate of 0.85 g corn per 1 g of weed in both years. Early-season CSWS was higher in weedy than weed-free corn and was most likely accounted for by water accessed by the approximately 10-fold higher weed than corn population. The differential in early-season CSWS between weedy and weed-free corn was highest at the 15- to 25-cm depth, and corn biomass was most correlated with this early-season CSWS values at 15 to 25 cm. Multisensor probes allowed quantitative assessment of soil-water changes within different soil layers during the growing seasons. These results suggest that the water deficit created by early root proliferation and water uptake by weeds specifically at 15 to 25 cm was most likely the cause of corn biomass reductions in these two experimental years.