CHEMICAL AND BIOCHEMICAL-CHANGES IN THE RHIZOSPHERES OF WHEAT AND CANOLA

Short-term root processes can influence chemical and biochemical condi tions at the soil-plant-root interface. In this study, soil phosphorus forms, pH and biochemical properties within and adjacent to the rhizo sphere of hard red spring wheat (Triticum aestivum L. 'Katepwa') and c anola (Brassica napus L. 'Westar') seedlings were studied over a 5-wk period. Soils were from the Ap horizon of a Calcareous Dark: Brown Che rnozemic soil (Lethbridge, Alta) and an Orthic Gray Luvisolic soil (Br eton, Alta) obtained from fertilized and unfertilized long-term contin uous-cropped and wheat-fallow rotation plots. Wheat and canola both ab sorbed more total phosphorus (P), produced more aboveground material a nd had higher dehydrogenase and alkaline phosphatase activities when g rown in Lethbridge soils than when grown in Breton soils. Canola took up more P from both the resin-extractable inorganic P (resin-Pi) and h ydrochloric acid extractable (HCl-Pi) fractions than wheat, indicating a greater ability to extract P from soil. Acid phosphatase levels inc reased over time in the rhizospheres of both wheat and canola. Dehydro genase activity was greater in the rhizospheres of wheat than of canol a, indicating greater microbial activity. Canola roots frequently lowe red pH within their rhizosphere which apparently suppressed microbial activity. Dehydrogenase activity in the relatively acidic Luvisolic so ils was lower than in the near-neutral Chemozemic soils. The plant-roo t chemical and biochemical changes in the rhizosphere varied depending on soil chemical characteristics and past soil management history. Re sults showed canola and wheat utilize different mechanisms to influenc e their root rhizospheres and obtain their nutritional requirements. R hizosphere changes were a function of plant species, soil type and pre vious soil management history.