The "root" to more soil carbon under pastures

Abstract

Recent interest in building soil carbon in pastoral systems is driven by the imperative to mitigate greenhouse gas emissions. It has been proposed that increasing root growth via deep rooting plants is a means of increasing soil carbon storage. Data on root depth distribution and production from a number of New Zealand studies are summarised to examine whether variation in root profiles can be manipulated and exploited. Most of the variation in root mass under grazed grass-clover pastures occurs in the upper 100 mm of soil. Changes in pasture management, such as soil fertility, grazing intensity and pasture species composition have a limited effect on root mass below this depth layer, of the order ±10-30%. Greater mass and length of roots in deeper soil layers under grazed grass-clover pastures is associated with lower soil fertility, drought stress and less commonly sown pasture species. The relationship between root mass (particularly deeper-root mass) and soil carbon storage has yet to be clearly established. Keywords: pasture species, root mass, soil carbon, soil fertility