Effect of conservation-tillage systems of cotton on surface runoff and its quality

Abstract

Various tillage systems for cotton were studied to determine their effects on the quantity and quality of surface runoff water under natural rainfall conditions in the Tennessee Valley region of northern Alabama. They included; reduced tillage without a cover crop (RT), reduced tillage with winter wheat as a cover crop (RTC), and conventional tillage (CT). Losses of sediment, plant nutrients, and pesticides were in the order of CT > RT > RTC in 1985. Runoff was the lowest from the RTC system, while the CT and RT systems had similar amounts of runoff. In 1986, runoff from the CT system was the lowest, followed by the RTC and RT systems, while sediment and pesticide losses were in the order of CT > RTC > RT. Mixed results were obtained for the losses of plant nutrients. The growth stage of cotton and the cultivation of the CT system influenced the patterns of runoff and sediment yield. More than 85% of the total sediment yield and 50 to 70% of the runoff approximately occurred during the first 2 months after planting. There were above average yields of seed cotton in 1985 from all systems, with the highest from the RT system. However in 1986, a drought during the critical stage of growth caused a reduction of yield from all systems, with the lowest yield from the RT system. Conservation-tillage systems were not beneficial to the cotton yield, over the conventional-tillage system, under the drought condition.