Budgets for root-derived C and litter-derived C: comparison between conventional tillage and no tillage soils

Placement of plant residues in conventional tillage (CT) and no-tillage (NT ) soils affects organic matter accumulation and the organization of the ass ociated soil food webs. Root-derived C inputs can be considerable and may a lso influence soil organic matter dynamics and soil food web organization. In order to differentiate and quantify C contributions from either roots or litter in CT and NT soils, a C-14 tracer method was used. To follow root-derived C, maize plants growing in the field were C-14 pulse -labeled, while the plant litter in those plots remained unlabeled. The C-1 4 was measured in NT and CT soils for the different C pools (shoots, roots, soil, soil respiration. microbial biomass). Litter-derived C was followed by applying C-14 labeled maize litter to plots which had previously grown u nlabeled maize plants. The C-14 pools measured for the litter-derived CT an d NT plots included organic matter, microbial biomass, soil respiration, an d soil organic C. Of the applied label in the root-derived C plots, 35-55, 6-8, 3, 1.6, and 0 .4-2.4% was recovered in the shoots, roots, soil, cumulative soil respirati on, and microbial biomass, respectively. The C-14 recovered in these pools did not differ between CT and NT treatments, supporting the hypothesis that the rhizosphere microbial biomass in NT and CT may be similar in utilizati on of root-derived C. Root exudates were estimated to be 8-13% of the appli ed label. In litter-derived C plots, the percentage of applied label recove red in the particulate organic matter (3.2-82%), microbial biomass (4-6%), or cumulative soil respiration (12.5-14.7%) was the same for CT and NT soil s. But the percentage of C-14 recovered in CT soil organic C (18-69%) was h igher than that in NT (12-43%), suggesting that particulate organic matter (POM) leaching and decomposition occurred at a higher rate in CT than in NT . Results indicate faster turnover of litter-derived C in the CT plots. (C) 2001 Elsevier Science Ltd. All rights reserved.