Investigation of Agricultural Loads in an Experimental Field under Varying Cultivation Practices and Weather Conditions

Agricultural diffuse pollution has widespread effects on the state of inland waters and the marine environment in the Baltic Sea region. A long-term field campaign was started in the Gårdskulla experimental field in Siuntio, Southern Finland, in 2007 to investigate the effects of the type of farming, different agricultural practices and activities, as well as weather conditions, on the quality of runoff water released from the field. In this study, a statistical analysis was performed on the discharge, nutrient and sediment data of the Gårdskulla experimental field. The objective was to investigate the factors that influence the discharge as well as the nutrient and sediment loads. In addition, discharge and nutrient loads representing the entire catchment, as processed from the VEMALA model results, were used as a reference to the field data. According to the results, the use of fertilizers in the experimental field during grain cultivation caused higher nitrogen loads in discharge compared to organic farming, there was a 62% decrease in annual total nitrogen load during organic farming compared to use of fertilizer for grain cultivation. A beef cattle pasture period caused higher phosphorus loads in discharge than other agricultural activities while grass period produced lower phosphorus loads. Beef cattle pasture period produced 60% higher annual phosphate load in drain discharge and 62% higher annual phosphate load in surface layer runoff than grass cultivation periods. The simulated discharge and nutrient loads showed similar seasonal variations as the field data. Meteorological forcing including precipitation, temperature and evapotranspiration were the main driving factors of discharge in the experimental field. Organic farming could significantly reduce the nitrogen loads in surface waterbodies, but controlling of the phosphorus loads by changing agricultural practices is more difficult than controlling nitrogen loads.