Effect of dairy cattle production systems on sustaining soil organic carbon storage in grasslands of northern Spain

Abstract

Predicting the regional net greenhouse gas emissions (Net GHG) of grasslands is increasingly important, as these are one of the most globally widespread vegetation types, providing several ecosystem services. In this study, we assessed the regional soil organic carbon (SOC) change over a 30-year period (1981-2010), and the annual GHG balance for 405,000 ha of moist temperate Spanish grassland associated with dairy cow production. To do this we used the following: (i) an integrated modelling framework comprising geographic information systems (GIS); (ii) the RothC model to simulate SOC changes in managed grasslands under moist temperate conditions; and (iii) Tier 2 recent IPCC methods to estimate emissions. The results showed an average regional SOC change rate of 0.16 Mg C ha −1 year −1 , associated with the initial SOC and livestock density. The annual GHG balance was positive, contributing to global warming by 5.6 Mg CO 2 -e ha −1 year −1 . Livestock density was the main factor affecting net GHG emissions in the grasslands associated with dairy production in northern Spain. We determined a livestock density threshold of 0.95 LU ha −1 , below which there is no SOC accumulation, and a threshold of approximately 0.4 LU ha −1 , above which net GHG per livestock unit (LU) are reduced. In conclusion, our study confirms the importance of dairy cow grazing systems in preserving and/or enhancing SOC stocks in the grasslands of northern Spain. It is therefore crucial to optimise the livestock density considering large variety of feed intake and alternative manure management mitigation options to reduce the net GHG emissions. KeywordsUpscaling • Soil organic carbon • Net greenhouse gas emissions • Grassland-based dairy systems * Asma Jebari

Climate change effects on northern Spanish grassland-based dairy livestock systems

“…However, excreta from other dairy cows and heifers are generally mixed with straw and other bedding and handled as solid manure (farmyard manure; FYM). Full details on the study area and dairy system characterisation can be found in Jebari et al (2022).…”

“…For RothC initialisation, carbon pools were estimated according to Weihermüller et al (2013), based on the clay content values from Rodríguez Martín et al (2016), and SOC stocks for the year 2010 obtained from the simulation results from a previous paper by Jebari et al (2022). The initial IOM pool was set to match the equation proposed by Falloon et al (1998) (Eq.…”

“…2. Initial SOC stocks were extracted for each municipality from a previous work (Jebari et al 2022) in which SOC stocks were simulated in the same study area for the period 1981-2010, using the aforementioned modified version of RothC (Jebari et al 2021).…”

“…The same assumptions were used to estimate carbon input derived from plant residues and the same mass-balance approach (by subtracting gross carbon production from total carbon ingestion by livestock) to predict the carbon input derived from animal manure, as in our previous work (Jebari et al 2022). Due to previously predicted negligible effects on GHG losses in the UK which has a similar climate (i.e., moist temperate), we did not consider inputs from feeding waste and bedding materials (McAuliffe et al 2018), and, further, we did not consider any change in the amount of the manure.…”

“…There are fewer studies covering the contribution of grassland-based livestock systems to global warming under climate change conditions in moist temperate systems (e.g., Graux et al (2012)). In Northern Spain, regional assessment of net GHG for grassland-based cattle production systems under moist temperate conditions was studied in Jebari et al (2022) under current conditions. However, to our knowledge, there have been no regional assessments of net GHG, under climate change conditions, in Northern Spain.…”