ROOT PRODUCTION OF A BARREL MEDIC (MEDICAGO-TRUNCATULA) PASTURE, A BARLEY GRASS (HORDEUM-LEPORINUM) PASTURE, AND A FABA BEAN (VICIA-FABA) CROP IN SOUTHERN AUSTRALIA

Total root biomass production of a grazed annual legume pasture (Medic ago truncatula); a grazed annual grass pasture (Hordeum leporinum), an d a grain legume crop (Vicia faba) was estimated using a sequential co ring and summation technique with corrections made for root death and decomposition during the season. Distribution of live root biomass wit h depth and C:N ratios of roots were also determined. Both in a dry se ason and in a season of average rainfall, total root biomass productio n of the 2 pasture species was similar and always greater than the fab a beans. Total root biomass production estimated using this technique was 60-200% greater than the maximum live root biomass, suggesting tha t there was significant root turnover during the season. In the dry se ason, the ratios of total root production to total shoot production we re 0.55, 0.57, and 0.32 for the barrel medic, barley grass, and faba b eans, respectively, and in the wetter season, the ratios were 0.40, 0. 42, and 0.25, respectively. Potential errors in the technique related to the recovery of root material and the decomposition of dead roots a nd old organic material are discussed, as are the implications of this information for soil organic matter dynamics.