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

Abstract

Total root biomass production of a grazed annual legume pasture (Medicago truncatula), a grazed annual grass pasture (Hordeum leporinum), and a grain legume crop (Vicia faba) was estimated using a sequential coring and summation technique with corrections made for root death and decomposition during the season. Distribution of live root biomass with depth and C: N ratios of roots were also determined. Both in a dry season and in a season of average rainfall, total root biomass production of the 2 pasture species was similar and always greater than the faba beans. Total root biomass production estimated using this technique was 60-200% greater than the maximum live root biomass, suggesting that there was significant root turnover during the season. In the dry season, the ratios of total root production to total shoot production were 0·55, 0·57, and 0·32 for the barrel medic, barley grass, and faba beans, 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 and old organic material are discussed, as are the implications of this information for soil organic matter dynamics.