## 3 Materials and Methods
### Process-Based or Conceptual Models
It incorporates the snowmelt process along with evapotranspiration and gives numerical solutions for overland (2D), unsaturated flow (1D), channel flow (1D) and saturated flow (3D). The combination of 'Daisy' and 'MIKE SHE' models enables water and nitrate simulation transport and overland flow on a catchment level, excluding intense rainfall events, i.e., Hortonian incidents [102]. Strict cropland's nitrogen-based fertilization regulations in (kg N ha\({}^{-1}\)) in Europe compel farmers to resort to alternative cultivating options, i.e., catch crops, to regulate post-harvesting nitrogen concentration of soil-rhizosphere nutrient balance. Some cultivations were tested over time, e.g., winter rye, spring barley, fodder radish, to achieve lower nitrogen leaching results. Simulation of the cultivation change during winter and spring, by using the biophysical agricultural production system simulator (APSIM) simulation model [103] (Figure 4), is parameterized over the mineralization of catch crops. Nitrate leaching was based on weighed percolation drainage within periods of interest. APSIM comprises certain modules, i.e., SurfaceOM, SoilN, SoilWat, canopy model and cultivar plant type. Each one of the modules simulates different fields of interest, e.g., water movement, N and C soil dynamics, plants' solar radiation competition, etc. SoilWat is a module of APSIM. It has been developed as a cascading water balance model in which, on a daily basis, water balance is estimated by simulating runoff, saturated/unsaturated water flow, solute ground and underground movement interrelated with saturated/unsaturated flow, plant transpiration and soil evaporation. The soil nitrogen module simulates nitrification, denitrification, urea hydrolysis, and nitrogen mineralization [104]. Nitrogen originated mainly by manure application over cropland and inorganic-based fertilizers [105]. APSIM's appliance entity (i.e., plant-rhizosphere-soil-atmosphere) functions on a daily time frame [103]. The prediction ensures reliable crop management strategies, all year long, for the sake of a balanced ecosystem, minimizing all negative environmental impacts as regards crop yield, water, nitrogen, and carbon mitigation dynamics [105]. Moreover, this model has been developed for sugarcane simulations, tested and confirmed at the paddock scale, since it incorporates modules for specific crops [106; 107]. Thus, it simulates management practices, water uptake and growth of sugarcane [104]. Intermediate percolation calculations are conducted by using the model EVACROP v.3.0, updated from EVACROP v.1.5 [108; 109]. Nitrogen leaching affects water quality and soil acidification. A bio-geophysical, process-based, multi-component ecosystem model (CoupModel) [110] was employed to estimate carbon and nitrogen fluxes, water and heat balance in the eco-terrestrial cycle. It facilitates the assessment of the local ecosystem (N) balance, e.g., manure application overtilage serving as biofertilizer. Nitrogen transformation includes (N) plant uptake and mineralization. It runs on a daily time frame  
Figure 3: Operational modules of DAISY, a nitrogen–water balance and transport model in croplands, with processed data interconnection/interrelation for complementary reasons. and on a minimal square meter unit grid. Model running requires certain parameters, i.e., weather (precipitation) data, solar radiation, temperature, relative humidity, wind speed, precipitation and dry deposition as regards (N) information. Carbon and nitrogen storage incorporates abiotic/inorganic, i.e., ammonium and nitrates in the soil, and biotic part, e.g., plant tissues and external characteristics such as leaf area and solar radiation exposure, which regulate carbon assimilation. The model regards the soil part as a series of constituent, interrelated layers where water, heat, nitrogen and carbon interact in a dynamic way. [PERSON]'s law and the generalized [PERSON] (1931) equations [100] for unsaturated conditions govern soil water flux.