**2.1. Study area**

After the 1950s, the area of arable land and the quantity of used mineral fertilisers worldwide and in Europe increased sharply [2]. Intensive agricultural production and greater density of animals have influenced on increased input of nitrogen on land and leaching into water bodies causing deterioration of groundwater and surface water resources quality. From the first serious attempt to change the impact of agriculture on water quality in Europe, with the adoption of the Nitrate Directive (91/676/EEC), it has been 25 years. Therefore, the main objectives of the expert community are to determine the transport and balance of nitrogen from agricultural land and its impact on water bodies and changing agricultural practices towards sustainable agriculture. The results of higher environmental awareness accompanied with measures adopted in agriculture policy can be seen in substantial gradual drop in consumption of mineral fertilisers in European Union (EU) member states [3]. These results were achieved through many different actions such as political decision of EU to act, designation of nitrate‐ vulnerable zones (NVZs) and establishment of Codes of Good Agricultural Practice for farmers on voluntary basis, establishment of action programmes to be implemented by farmers within NVZs, and establishment of national monitoring and reporting system every 4 years for each member state [3]. To be more precise, there are some measures within cover action programmes which are crucial for the success, such as regular education of farmers, subsidy payments, cross‐compliance in agriculture, implementation of new crop varieties, organic and no‐till farming, promoting a 3‐year rotational scheme, promoting nitrogen fixation plants, green

In Slovenia, groundwater accounts for 98% of all sources of drinking water supply, so the effective protection of groundwater quality is of the utmost importance for the health of the population [4, 5]. But unfortunately, main areas of groundwater resources such as Drava Plain in Slovenia spatially coincide with the most intensive agricultural areas. Therefore, is nitrogen in these areas together with the plant protection products the main groundwater pollutant? Coincidence of natural geological and climate conditions, development in agriculture pro‐ duction management and past inappropriate decisions by authorities caused that many of drinking groundwater sources are at a high risk or even not suitable for use [6]. While Slovenia assigns the whole country as nitrate‐vulnerable zone by Nitrate Directive and almost all farmers implemented Codes of Good Agricultural Practice, areas of additional special protection of drinking water groundwater resources are defined as water protection areas (WPAs). The basic function of WPA is conservation of drinking water quality of all water resources, which are intended for the supply of the population. Each of the EU member states committed themselves to the Water Framework Directive (2000/60/EC) with aim to implement a variety of environmental measures and maintain or improve good quantitative and chemical status of all groundwater and surface water bodies [7]. On this basis, each member state had to prepare river basin management plans and define water bodies' quality status and actions to achieve ultimate WFD goal of good water quality. All actions and quality status are carefully monitored and reported to European commission. In the case that member state in not fulfilling its own plan European Commission begins process of determining liability which could lead to the imposition of a fine to member state. One of the reporting activates of each member state is also annual report on gross nitrogen budget (GNB) and net nitrogen budget (NNG) which is prepared on the basis of Eurostat/OECD methodology [8]. The GNB is calculated as the

manure plants and nitrogen catch crops, and so on.

114 Water Quality

The River Drava Plain (Dravsko polje) aquifer study area (293.2 km2 ) is located in the north‐ eastern part of Slovenia (**Figure 1**). The Drava Plain altitude is relatively small and ranges between 200 and 250 m without any distinct slopes. The plain is divided on four alluvial terraces. The agricultural land lies above an intergranular aquifer with specific soil character‐ istics which are the result of the deposition of river sediments. The river Drava deposited sediments of Quaternary sand and gravel in the area which forms extensive alluvial aquifer. The aquifer is very well permeable with the permeability coefficient of about 5 × 10‐3 m/s. The aquifer is unconfined and exposed to the intake of pollutants from the surface. The area is suitable for intensive agriculture (grain production) due to the favourable terrain and structure of land ownership. According to data on land use prevails arable (44%) followed by the forest (20%), urban (19%) and grassland (9%). Other land‐use classes are represented by 1% or less. Soils are shallow and contain many sand particles and larger rocks. Due to continental climate with spring rainfall and hot and relatively dry summers, drought often occurs on these soils.

**Figure 1.** The river Drava Plain study area land use, elevation and water protection area.

Geographically speaking, the Drava Plain area is located in sub‐Pannonian Slovenia, which is characterised by continental to sub‐continental climate, with lowest rainfall quality in winter and spring months (January to April) and the highest in the summer months (June to Sep‐ tember) due to typical stormy rainfall events. The average annual rainfall amounts (1981–2010) measured at the Maribor Airport and Ptuj were 935 and 959 mm, respectively. The average annual minimum temperature measured at the Maribor Airport was 5.3°C and maximum 15.3°C. The average minimum temperature for the meteorological winter (December to February) was −3.8°C and meteorological summer (June‐August) 25.4°C.

In the area of the river Drava Plain, two regulations on water protection areas are in force, which protect the aquifer as the primary source of drinking water in the area. The measured concentration of nitrate (NO3 − ) in groundwater is at many monitoring points, in excess of the WFD‐recommended concentrations for drinking water (50 mg NO3 − /l) (**Figure 2**).

Modelling Impact of Adjusted Agricultural Practices on Nitrogen Leaching to Groundwater http://dx.doi.org/10.5772/66324 117

**Figure 2.** Average annual nitrate concentration (mg NO3 − /l) for Drava aquifer between 1998 and 2014 calculated by Slovenian Environmental Agency on the basis of several monitoring points.

Three research locations were included in the study (**Figure 1**): Dobrovce (253 m.a.s.l.) mostly vegetable horticultural production, narrowest WPZ zone I (1.53 ha); Maribor (262 m.a.s.l.) with a grain crop rotation, narrow WPZ zone II (15.12 ha); Ptuj (218 m.a.s.l.) mixed crop rotation for seed production, wider WPZ zone III (2.25 ha) (**Figure 1**).

### **2.2. SWAT model description**

sediments of Quaternary sand and gravel in the area which forms extensive alluvial aquifer. The aquifer is very well permeable with the permeability coefficient of about 5 × 10‐3 m/s. The aquifer is unconfined and exposed to the intake of pollutants from the surface. The area is suitable for intensive agriculture (grain production) due to the favourable terrain and structure of land ownership. According to data on land use prevails arable (44%) followed by the forest (20%), urban (19%) and grassland (9%). Other land‐use classes are represented by 1% or less. Soils are shallow and contain many sand particles and larger rocks. Due to continental climate with spring rainfall and hot and relatively dry summers, drought often occurs on these soils.

**Figure 1.** The river Drava Plain study area land use, elevation and water protection area.

February) was −3.8°C and meteorological summer (June‐August) 25.4°C.

−

WFD‐recommended concentrations for drinking water (50 mg NO3

concentration of nitrate (NO3

116 Water Quality

Geographically speaking, the Drava Plain area is located in sub‐Pannonian Slovenia, which is characterised by continental to sub‐continental climate, with lowest rainfall quality in winter and spring months (January to April) and the highest in the summer months (June to Sep‐ tember) due to typical stormy rainfall events. The average annual rainfall amounts (1981–2010) measured at the Maribor Airport and Ptuj were 935 and 959 mm, respectively. The average annual minimum temperature measured at the Maribor Airport was 5.3°C and maximum 15.3°C. The average minimum temperature for the meteorological winter (December to

In the area of the river Drava Plain, two regulations on water protection areas are in force, which protect the aquifer as the primary source of drinking water in the area. The measured

) in groundwater is at many monitoring points, in excess of the

−

/l) (**Figure 2**).

Processes in the unsaturated zone were modelled with the Soil and Water Assessment Tool model ArcSWAT version 2009.10.1 [16]. The model was developed to assist water managers in evaluating the impact of agricultural activities in the river basins. The core of the model was developed in the early 1990s under the United States Department of Agriculture (USDA). The model was at the beginning called SWRRB and was created by joining three existing models CREAMS, EPIC and GLEAMS [12].

The SWAT model has the capability to predict the impact of land use and land management on the water quality and quantity and transport of sediment and soluble materials from agriculture in large river basins with the complex heterogeneous topography, soils, land use and land management conditions over long periods of time [12]. It is capable of modelling numerous agricultural management practises, agri‐environmental measures, climate changes, scenarios of future land‐use development, plant growth and biomass development. It operates on annual, monthly, daily and even on hourly time scale. Its open source code enables scientists to connect the model with others such as APEX, ALMANAC and MODFLOW and upgrade it for better performance such as SWIM and SWAT‐G [12, 17, 18].

Diffuse sources of nutrients and their transport routes are in the SWAT model strongly linked to the water cycle, which is influenced by water and solar energy. When precipitation falls on the soil, it may follow different preferential pathways such as surface runoff or shallow subsurface runoff (transfer of N and P) and vertical leaching into the shallow aquifer (transfer of N). The nitrogen balance in the soil and groundwater depends on many factors (biological, climatic and physico‐chemical properties of the soil). Detailed explanation of the SWAT model strengths, weaknesses, opportunities and threats in catchment modelling is given in preceding book chapter [19].

### **2.3. Database**

For the preparation of the model, data were collected ranging from spatial data (digital elevation model (DEM) map, land‐use map and classification and soil map and its properties), time series (weather such as daily precipitation, temperature, solar radiation, wind speed, relative humidity; crop rotations such as type of farmed culture, crop rotation sowing and harvesting dates; tillage such as the type of tillage and machines, the time of basic soil preparation, cultivation during growth and after; fertilisation such as the type, time of use, quantity and nutrient content), attribute data (soil parameters such as thickness of horizons, hydrological group, bulk density, texture, colour, rocks, organic matter, hydraulic conductivity, plant available water and soil erosivity—MUSLE; plant growth such as leaf area index, the development of dry biomass and average yield) to data for model calibration (soil water content (SWC)) (**Table 1**). Information about the type, quantities and dates of the use of fertiliser was obtained from Agricultural Extension Service (Chamber of Agriculture and Forestry of Slovenia—Unit Maribor) and farmers. Data acquisition began in early July 2011, and lasted over the entire period of the survey until 2013. When the data were collected, they were during the research gradually entered in the SWAT model to prepare a base scenario of the base current agricultural practices in all three research locations. This was a base for further development of scenarios of potential crop rotations including good agricultural practices for protecting water protection zones (WPZs) in the Drava Plain area.

### **2.4. Agricultural land management scenarios**

The scenarios were developed with the aim to determine how changes in agricultural practices (crop rotation, fertilisation rate and type of plant varieties) influence the leaching of nitrogen below the plant roots from the soil profile. In designing the scenarios, we relied on the guidelines for the scientifically grounded fertilisation, issued by the Ministry of Agriculture, Forestry and Food [20], own expertise and information from agricultural producers (farmers) in the study area.

Depending on the availability of data, we prepared a total of seven sets of scenarios with 31 possible combinations of alternative rotations and managements (A. Basic rotations with modified fertilising norms, B. Basic rotations with introduced new crops, C. Grassland use, D. The most common rotations in the research area, E. Adapted the most common rotations, F. Organic rotations, G. Water protection zones regime rotations) (**Table 2**). Scenarios can serve only as indicative information as actual future development of agricultural land management is impossible to predict. EU Common Agricultural Policy (CAP) changes at least once in 7 years with possible mid‐term changes in each of the member states after evaluation of the national Rural Development Programmes (RDPs). Agricultural policy can throughout financial stimulants dictates simultaneous sustainable agriculture and protection of water resources. In designing the scenarios, we relied on the guidelines for professionally justified fertilisation, issued by the Ministry of Agriculture, Forestry and Food [20], own expertise and on informa‐ tion from farmers.


**Table 1.** Model input database.

Diffuse sources of nutrients and their transport routes are in the SWAT model strongly linked to the water cycle, which is influenced by water and solar energy. When precipitation falls on the soil, it may follow different preferential pathways such as surface runoff or shallow subsurface runoff (transfer of N and P) and vertical leaching into the shallow aquifer (transfer of N). The nitrogen balance in the soil and groundwater depends on many factors (biological, climatic and physico‐chemical properties of the soil). Detailed explanation of the SWAT model strengths, weaknesses, opportunities and threats in catchment modelling is given in preceding

For the preparation of the model, data were collected ranging from spatial data (digital elevation model (DEM) map, land‐use map and classification and soil map and its properties), time series (weather such as daily precipitation, temperature, solar radiation, wind speed, relative humidity; crop rotations such as type of farmed culture, crop rotation sowing and harvesting dates; tillage such as the type of tillage and machines, the time of basic soil preparation, cultivation during growth and after; fertilisation such as the type, time of use, quantity and nutrient content), attribute data (soil parameters such as thickness of horizons, hydrological group, bulk density, texture, colour, rocks, organic matter, hydraulic conductivity, plant available water and soil erosivity—MUSLE; plant growth such as leaf area index, the development of dry biomass and average yield) to data for model calibration (soil water content (SWC)) (**Table 1**). Information about the type, quantities and dates of the use of fertiliser was obtained from Agricultural Extension Service (Chamber of Agriculture and Forestry of Slovenia—Unit Maribor) and farmers. Data acquisition began in early July 2011, and lasted over the entire period of the survey until 2013. When the data were collected, they were during the research gradually entered in the SWAT model to prepare a base scenario of the base current agricultural practices in all three research locations. This was a base for further development of scenarios of potential crop rotations including good agricultural practices for protecting

The scenarios were developed with the aim to determine how changes in agricultural practices (crop rotation, fertilisation rate and type of plant varieties) influence the leaching of nitrogen below the plant roots from the soil profile. In designing the scenarios, we relied on the guidelines for the scientifically grounded fertilisation, issued by the Ministry of Agriculture, Forestry and Food [20], own expertise and information from agricultural producers (farmers)

Depending on the availability of data, we prepared a total of seven sets of scenarios with 31 possible combinations of alternative rotations and managements (A. Basic rotations with modified fertilising norms, B. Basic rotations with introduced new crops, C. Grassland use, D. The most common rotations in the research area, E. Adapted the most common rotations, F. Organic rotations, G. Water protection zones regime rotations) (**Table 2**). Scenarios can serve only as indicative information as actual future development of agricultural land management

water protection zones (WPZs) in the Drava Plain area.

**2.4. Agricultural land management scenarios**

in the study area.

book chapter [19].

**2.3. Database**

118 Water Quality



*Key:* ca, cabbage; tn, turnip; on, onion; po, potatoes; pe, peppers; or, oilseed rape; cl, clover; co, corn; ww, winter wheat; wb, winter barley; bw, buckwheat; fp, field peas; cas, cabbage for seeds; BMP, best management practices according to guidelines for the scientifically grounded fertilisation [20]; WPZ, water protection zone; I, narrowest WPZ zone (stricter regime); II, narrow WPZ zone; III, wider WPZ zone.

**Table 2.** Agricultural land management scenarios.

In the first set (A.) are three scenarios for Maribor and Ptuj, where fertilisation of basic rotation changed depending on the quantity of yield (A. Scenarios 1–3) and one with organic fertiliser (cattle slurry) introduced in to rotation with strictly mineral fertilisers (5). For the location of Dobrovce, organic fertilisers are replaced by mineral (Scenario 4). In the second set (B.) is one scenario for the Maribor rotation, where soya replaced corn (Scenario 6) and three scenarios for Dobrovce with alternative vegetable rotations, with one legume as a main crop and winter greening (Scenarios 11–13). In the third set (C.) are four scenarios including four‐cut, three‐cut, two‐cut and extensive one‐cut (no fertilisers) grassland (Scenarios 7–10). In the fourth set (D.) are average cattle/dairy, pig, arable rotation and for the research area typical permanent grassland management (Scenarios 14–17). In the fifth set (E.) are two variations of modified cattle/dairy and pig rotations, one without organic fertilisers (Scenarios 18 and 20) and the other with soya replacing corn (Scenarios 19 and 21). In the sixth set (F.) are average horticul‐ tural (vegetable) and organic rotation (Scenarios 22 and 23). In the seventh set (G.) are average cattle/dairy, pig, arable rotation and permanent grassland management with included fertilisation rates required in WPA (Scenarios 24–31). The results of the alternative scenarios were compared with the baseline scenarios (business as usual).
