CARBON FLUXES IN THE RHIZOSPHERE OF WINTER-WHEAT AND SPRING BARLEY WITH CONVENTIONAL VS INTEGRATED FARMING

Estimates of rhizosphere C budgets for winter wheat and spring barley under conventional (CONV) or integrated (INT) management were obtained using a combination of crop growth measurements, C-14 pulse-labelling and a model rhizodeposition technique. In both crops the proportion o f C-14 allocated to shoots 3 wk after labelling increased with the dev elopmental stage, which resulted in maximum belowground C fluxes at ti llering. At this stage C-14 released from the roots was relatively mor e in organic form in wheat and more as CO2 in barley, and this was ref lected in the C fluxes accumulated over the growing season. In wheat n o significant effect of management on C-14 allocation was found. In ba rley relatively more C-14 tended to be transferred to roots in CONV th an in INT, and this was reflected in considerably higher calculated ro ot growth, root respiration and rhizodeposition fluxes in CONV than in INT. Therefore, the hypothesis that plants invest more in roots and r hizodeposition in the system with lower nutrient input (INT) was rejec ted. Total rhizodeposition, including root decay, amounted to 450-990 kg C ha(-1) y(-1) (7-15% of net assimilation) which was twice the quan tity of roots left at crop harvest. The relevance for microbe-mediated processes in relation to soil fertility is pointed out.