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

Net changes of soil C stocks in two grassland soils 26 months after simulated pasture renovation including biochar addition

“…As suggested by Dodd et al . (), it may be difficult to increase C stocks of New Zealand pastoral soils with relatively high C in the 0‐ to 10‐cm‐depth zone where soils may be near or close to the upper limit for C accumulation. Recently, Beare et al .…”

“…Strategies to manage pasture and soil so that this temporary loss is prevented, offset, or rapidly refilled should thus be considered. In fact, the use of deep‐rooting pastures has been proposed as a management practice to allocate more C at depth (Carter & Gregorich, ; Dodd et al ., ), although this can be hampered by physical (Carter & Gregorich, ) and nutrient constraints of subsurface horizons (Dodd et al ., ).…”

An assessment of the role of soil organic matter in pasture resilience

“…In terms of C return to the rhizosphere, most NZ pastures are very shallow rooted. From data on dairy soils, often with >80% of roots in the top 100 mm of the soil profile (Dodd et al 2011), there is potential to move C into deeper layers of the profile, which have low C saturation, by increasing rooting depth or…”

Direct and indirect effects of resilient pastures at farm scale

“…Climate conditions suggest that summer-autumn extreme dry/drought has been a major factor limiting persistence (Jagger 2009). Perennial ryegrass has a shallow root system (Dodd et al 2011), especially in compacted soils (Crush & Thom 2011), which makes it susceptible to drought. This results in poor summer growth which in turn can increase susceptibility to insect damage, pulling damage and weed ingression in pasture (Clark 2011).…”