Water Use and Yield of Canola under Dryland Conditions in the Central Great Plains

Reduced tillage systems, compared with conventional tillage methods, have increased precipitation storage efficiencies and increased the amount of available water for crop production in the central Great Plains. Increased available water affords producers the opportunity to diversify and intensify their production systems from the traditional wheat (Triticum aestivum L.)-fallow system. This study was conducted to determine canola (Brassica napus L.) production potential under the limited and variable precipitation patterns found in dryland agricultural systems in northeastern Colorado. Water stress timing effects on canola yield components were determined under a rainout shelter in 1993 and 1994, with water withheld during either the vegetative, reproductive, or grain-filling growth stage. All treatments received the same total water application, equal to the long-term average growing season precipitation. Rooting depth was determined from water extraction patterns monitored with a neutron probe. A water use-yield function was determined for canola grown under a line-source gradient irrigation system. A non-water-stressed baseline was determined for future water stress research using an infrared thermometer in canola. Timing of water stress did not significantly affect yield. Canola can extract water from soil depths of 65 in., but 92 to 95% of total seasonal water use comes from growing season precipitation and water extracted from soil depths above 47 in. An examination of the growing season precipitation records indicates that canola yields could range from 284 to 2358 lb/acre (averaging 1020 lb/acre), assuming 4 in. of stored soil water use in addition to precipitation. Dryland canola production may not be economically viable for northeastern Colorado at current market prices and yields.