The trade-offs between milk production and soil organic carbon storage in dairy systems under different management and environmental factors

Abstract

A possible agricultural climate change mitigation option is to increase the amount of soil organic carbon (SOC). Conversely, some factors might lead to inadvertent losses of SOC. Here, we explore the effect of various management options and environmental changes on SOC storage and milk production of dairy pastures in New Zealand. We used CenW 4.1, a process-based ecophysiological model, to run a range of scenarios to assess the effects of changes in management options, plant properties and environmental factors on SOC and milk production. We tested the model by using 2years of observations of the exchanges of water and CO measured with an eddy covariance system on a dairy farm in New Zealand's Waikato region. We obtained excellent agreement between the model and observations, especially for evapotranspiration and net photosynthesis. For the scenario analysis, we found that SOC could be increased through supplying supplemental feed, increasing fertiliser application, or increasing water availability through irrigation on very dry sites, but SOC decreased again for larger increases in water availability. Soil warming strongly reduced SOC. For other changes in key properties, such as changes in soil water-holding capacity and plant root:shoot ratios, SOC changes were often negatively correlated with changes in milk production. The work showed that changes in SOC were determined by the complex interplay between (1) changes in net primary production; (2) the carbon fraction taken off-site through grazing; (3) carbon allocation within the system between labile and stabilised SOC; and (4) changes in SOC decomposition rates. There is a particularly important trade-off between carbon either being removed by grazing or remaining on site and available for SOC formation. Changes in SOC cannot be fully understood unless all four factors are considered together in an overall assessment.

Modeling Carbon and Water Fluxes of Managed Grasslands: Comparing Flux Variability and Net Carbon Budgets between Grazed and Mowed Systems

“…The soil organic matter module of the model was derived from the CENTURY model [55], which was originally developed for grasslands (more details are given in Section 2.2). Recently, CenW was successfully parameterized and used to simulate carbon and water fluxes of an intensively grazed dairy pasture in New Zealand [56], and to test effects of different climate and management practices on soil carbon stocks and milk production [57].…”

Response of Grazing Land Soil Health to Management Strategies: A Summary Review

“…Therefore, these lands play an important role in mitigating greenhouse gas emission. Soil C sequestration in grazing lands is controlled by above-ground and below-ground plant composition and inputs, C lost from animal consumption, soil characteristics, C distribution in labile and stable pools, and litter and root deposition and decomposition rates [50][51][52][53][54][55][56][57][58][59]. Management strategies such as adjusting stocking rates to regulate the vegetation utilization rate [16] and adoption of improved grass species or conversion from agricultural lands or woodlands to grasslands would increase C input and potentially promote soil C accumulation [3,60].…”

“…Applying fertilizer on grazing land can improve plant production because nutrients are needed to meet the plant growth demand [114]. At the same time, litter and root production and turnover can be increased to promote soil C sequestration [50,60,61,115]. Conversely, ecosystems under limited soil nutrients can decrease C sequestration due to the competition between plant and soil microbes [116][117][118].…”

“…Together with the fertilizer application, irrigation can also improve soil C [121,122]. It should be noted that the benefit of irrigation on soil C may only be realized in dry areas [50]. Conversely, excess water may decrease soil C accumulation [50] because of higher soil respiration [123] or lower C input (root biomass) to soil [124,125].…”

“…It should be noted that the benefit of irrigation on soil C may only be realized in dry areas [50]. Conversely, excess water may decrease soil C accumulation [50] because of higher soil respiration [123] or lower C input (root biomass) to soil [124,125]. Moreover, the response of soil C to irrigation sometimes may only be observed under long-term management [122,126].…”