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

This paper assesses the role of soil organic matter (SOM) in pasture resilience and longevity. New Zealand pasture soils have high levels of SOM, which contribute to soil structural stability and nutrient cycling, functions that support resilient pasture. It is concluded that pasture resilience requires (a) a pasture-soil system that returns regular amounts of fresh, ‘labile’ carbon (C) since this younger SOM fraction plays a significant role in these processes, and (b) a thriving soil biota that can rapidly turn over this labile C. Pasture itself also plays a critical role as the major pathway for C transfer into the soil rhizosphere, with differences between species in amounts and composition of C returns. Resident (older) SOM should not be ignored and plays a role in sustaining soil structure, but the younger SOM is the fraction that turns over more often and plays a key role in nutrient supply. Soil organic matter is not a single solution to increasing pasture resilience since soil type and summer rainfall have been previously identified as key factors also. However, other identified factors such as plant nitrogen status, plant population dynamics and grazing management either influence or are influenced by the turnover of SOM, suggesting its role in pasture resilience should not be underestimated.