# Seasonal Net Carbon Exchange in Rotation Crops in the Temperate Climate of Central Lithuania
## 1 Introduction  
Croplands represent about 12% of the Earth's surface [1] and one-third of the land surface in Europe [2]; therefore, it plays a significant role in the generation of anthropogenic emissions. Globally, agriculture accounts for 10-12% of the total anthropogenic emissions of greenhouse gas (GHG) [3], 9.78% in the EU, out of which 4.94% are emissions from the soil [4]. Agriculture produces nearly 21.4% of the total emissions in Lithuania [5]. Soil is an important (and the largest) carbon reservoir, which accumulates about 53% of terrestrial carbon [6]. The main source of carbon is plant biomass (andresidues) in the soil [7]. The dissolved soil carbon may be lost not only by leaching but by the uptake of plants and by removal from harvesting as well [8; 9]. C exchange is released through photosynthesis assimilating atmospheric CO\({}_{2}\) and organism respiration (R) emitting CO\({}_{2}\) in the system atmosphere-biosphere. CO\({}_{2}\) rates assimilated by the ecosystem are considered gross primary production (_GPP_) [10]. The net ecosystem production (_NEP_) is the net C rate accumulated in biomass. _NEP_ is defined as the difference between _GPP_ and ecosystem respiration (R) [11; 12]. All rates of C exchange are dependent on the anthropogenic and environmental factors. It is estimated that 89% of the GHG emissions in the agricultural sector could be reduced by reducing CO\({}_{2}\) emissions. Therefore, the agroecosystems essentially contribute to the sink of large amounts of carbon from the atmosphere [13]. The ecosystem C exchange is related to the seasonal changes in environmental conditions and plant growth [14; 15]. Ambient moisture and temperature directly affect the activity of plant enzymes and, thus, conditioned the photosynthesis intensity and rates of assimilated CO\({}_{2}\)[16]. It is accepted that photosynthesis is the initial physiological process that responds to changes in temperature [8]. In addition, photosynthesis is performed by the leaf area (LAI) which is development-depended on growth stages and environment conditions [14; 17]. The deterioration of the environmental systems and the unsustainable exploitation of natural resources, both globally and locally, have been assumed such significance that, recently, high-level political meetings aimed at building a low-carbon and resource efficient economy have been undertaken [11; 18]. The intelligent agricultural solutions require data on the environmental impacts of agriculture. In order for operationalize decision-making for sustainable agriculture, one needs to establish the corresponding datasets and protocols. Crop rotation, growth period and water content are the factors that determine C sequestration [10; 15], CO\({}_{2}\) fluxes and exchange in the system atmosphere-plant-soil [19]. A strong correlation between the CO\({}_{2}\) emission temperature and precipitation (\(r=0.7\)) was found during the summer season in organic and conventional agroecosystems [15; 20]. As conventional farming systems remain directed toward productivity for greater profits rather than for soil fertility and the maintenance of a sustainable environment, conventional farming has a significant negative impact on the long-term soil productivity and sustainable agroecosystem. The control of the grown yield and carbon sequestration becomes possible if the appropriate farming system, growing technology and crops are chosen [21; 22; 23]. The relationship between the rates of carbon fluxes and bio-parameters of the plants stand important for the evaluation of the possibility for climate change mitigation and the development of a sustainable agriculture. Evidence of the crop _NEP_ would improve the understanding of the factors and mechanisms that influence carbon emissions and sequestration and, thus, optimally regulate these processes, thereby reducing CO\({}_{2}\) emissions and predicting their changes.