Dry matter production of oilseed rape (Brassica napus) with special reference to the root system

At the research farm of the Swedish University of Agricultural Sciences, Uppsala, above- and belowground production and changes with time in root length, mean root radius and root surface area of spring oilseed rape were studied during the growing seasons 1987 and 1990. In both years, the highest root growth rate was recorded during the stem elongation phase, and the highest shoot growth rate during flowering. The root: shoot ratio decreased throughout the whole period of root sampling, from 0.64 to 0.16, during the cool and wet first year. In the warmer and drier second year, the ratio increased to a maximum of 0.72 when flowering started, and thereafter decreased. More than 80% of the root dry matter was found in the topsoil. Roots were longer and thinner in the dry and warm 1990 than in the wet and cool 1987. Maximum root length was c. 4.9 km/m(2) in 1990, and mean root radius varied between 0.1 and 0.7 mm. Increases in root surface area during periods of root growth were due to increased root length rather than to increased mean root radius.