## 1 Introduction  
Managed grasslands and rangelands represent ~70% of global agricultural area [1], which is 25% of the Earth's ice-free land surface [2]. The soils of these agroecosystems contain ~20% of the world's soil organic carbon (SOC) stocks, which implies that they play a significant role in the global carbon and water cycles [3; 4; 5; 6; 7]. In Europe, grasslands cover 22% of the land area [8], where management practices and climate strongly influence their C sequestration rates. Average annual estimates of carbon balances of temperate grasslands for EU countries ranged from being a C source of 45 kg C ha\({}^{-1}\) year\({}^{-1}\) to a C sink of 400 kg C ha\({}^{-1}\) year\({}^{-1}\)[9]. Hence, these managed agroecosystems may contribute to the mitigation of climate change [7; 10; 11; 12]. However, these ecosystems are particularly complex and difficult to investigate because of the wide range of management and environmental conditions that they are exposed to, leading to a large variability in their CO2 source/sink capacity [5; 13; 14; 15; 16; 17]. Most of the vegetation growing on pastoral lands is used to either feed animals directly (grazing), or it is harvested and used to feed animals at other times or locations (mowing). grasslands managed through mowing are fundamentally different to grassland managed through grazing with respect to their above ground biomass removal patterns, export and cycling of carbon, and applications of fertilizer, as more nitrogen is returned to the field during grazing through animals excreta compared to moving where almost everything is exported from the system [15; 18]. In addition, there is large uncertainties about the effects of mowing and grazing on different ecological processes related to their C cycle [19; 20; 16]. The frequency and intensity of foliage removal and its fate (grazed on site or moved and exported) have effects on the carbon budgets but also on the nutrient cycling and development of the grassland [7; 21; 22]. Grazing intensity showed to have significant effect on the soil carbon sequestration potential of grassland ecosystems. Positive C sequestration was reported for light-to-moderate grazing intensities [11; 23], while overgrazing or trampling were found to have a negative effect on SOC stocks [24]. Although less studied than grazing systems [25], mowing is usually related to important losses of soil organic carbon unless manure is returned to the paddock because of the export of biomass from the grassland that reduces the amount of C inputs to the agroecosystem [26]. However, previous studies found that soil carbon stocks of mowed grassland could also increase depending on the cutting/harvesting intensity [8; 18]. Direct and accurate measurements of small changes in soil organic carbon stocks over short time periods in response to different management practices are difficult to achieve because of the large spatial variability of SOC and of the large C content of the soil relative to the rate of change [27; 28; 29]. Despite the uncertainties associated with flux measurements, eddy covariance (EC) is a powerful tool for measuring ecosystem/atmosphere carbon fluxes [8; 30; 31; 32]. With EC, it is possible to detect changes in net ecosystem exchange (NEE) of carbon at a half-hourly time resolution, which enables estimates to be made of whether land management practices result in systems being net sinks or sources of CO2[12; 26]. NEE is the balance of gross primary production (GPP) and ecosystem respiration (ER) and it represents the net exchange of CO2 between the atmosphere and terrestrial ecosystems. For managed ecosystems, the carbon balance has to comprise NEE and C losses (harvested biomass, enteric fermentation, export of animal products, and organic and inorganic C losses through leaching and erosion) as well as nonphotosynthetic carbon gains (organic fertilization), resulting in the net biome productivity (NBP = NEE + carbon export - carbon import (positive value indicates that the ecosystem is a carbon source).