Corn and Velvetleaf (Abutilon theophrasti) Water Use Efficiency.

Rainfall and soil water availability during the growing season is highly variable throughout Nebraska and the north central USA, which greatly impacts agroecosystems and their management, including the presence and abundance of weedy species. The supply of soil resources is critical for the establishment and long-term competitive success of a plant species. While there is considerable research on the effects of water supply on crop growth and productivity, there is little published research on the response of weedy and invasive plants to limiting soil water supply relative to that of the crop. The objective of this study was to determine the water use efficiency (WUE) of corn and velvetleaf under varying levels of constant water supply. Prior to the start of the experiment, 0.90 mil black plastic bags were placed inside pots (25 cm diam by 23 cm deep). Corn and velvetleaf plants were seeded in the pots filled with a constant 13.5 kg dry weight of a 8:1:1 mixture of soil:sand:perlite. Plants were thinned to one plant per pot with bags sealed around the base of the plant stem so the only water loss was that due to transpiration. Sealed access tubes were inserted through the bags to allow daily water replacement with minimal disturbance of plants. Daily transpiration was measured by weighing the pots at the same time each day.  Soil water content was maintained at low, medium or high levels (fraction of transpirable soil water at which 1/3, 2/3 and 1.0 full transpiration occurs). Plants were harvested periodically at differing stages of development to determine leaf area and biomass. Above-ground biomass was regressed on cumulative water use with the slope providing an estimate of water use efficiency. Corn WUE was always 25-35% greater than that for velvetleaf. Corn WUE was greatest (13.46 g/kg) in the low and smallest (7.27 g/kg) in the high water treatment in the first trial. Similarly, velvetleaf WUE was greatest (10.45 g/kg) in the low and smallest (5.11 g/kg) in the high water treatment. The trends were similar in the second trial, but WUE was about 30% smaller overall. Results from this study indicate that corn has greater WUE than velvetleaf.