V. KOLEVA, D. STOICHEVA and D. STOICHEV
N. Poushkarov Institute of Soil Science, BG-1080 Sofia, Bulgaria
KOLEVA, V., D. STOICHEVA and D. STOICHEV, 2002. Application of simplified model for determination of critical nitrogen loads for ground water protection. Bulg. J. Agric. Sci., 8: 561–568
A critical load of a pollutant is the level of input above which some harmful ecological effects on specified sensitive elements of the ecosystem occur. Critical loads are being used in policy decisions regarding reduction of air pollution emissions. The critical loads concept is widely used in calculation of critical loads for nitrogen and sulphur on forest ecosystems and there are very few studies on arable soils. Besides the background atmospheric acid depositions, arable soils receive purposefully induced nitrogen loading in the form of fertilizers, which not in all cases are fully included in the biological cycle of nutrients and turn into a pollutant with respect to groundwater. Determination of critical nitrogen loads is a possible tool to control nitrogen input with regard to a selected criterion. Here is presented a case study on assessment of critical nitrogen loads on arable Fluvisol. The calculation is made on the basis of data received from the area of long-term fertilizer experiment with maize grown as a monoculture. For the assessment was applied a simplified equation which describes the connection between the groundwater and nitrogen loading. In the equation as a variables are included: long-term average nitrogen uptake by plants, immobilised nitrogen and average annual drainage flux out of the soil root zone. As a critical limit for the calculation was used the maximum concentration level for nitrates in the drinking water (50 ppm). The received critical nitrogen load equals to 13 330 eq.ha–1.yr–1. (N = 187 kg.ha–1.yr–1). In case that the annual nitrogen input exceeds this limit a precondition for nitrate pollution of the shallow groundwater occur.