Long-term Mass Balance on Arable Fluvisol for Determination of Critical Nitrogen Loads in Terms of Soil Acidification

V. KOLEVA, D. STOICHEVA, D. DONOV and D. STOICHEV
N. Poushkarov Institute of Soil Science, BG-1080 Sofia, Bulgaria

Abstract

V. KOLEVA., D. STOICHEVA, D. DONOV and D. STOICHEV , 2003. Long-term mass balance on arable Fluvisol for determination of critical nitrogen loads in terms of soil acidification. Bulg. J. Agric. Sci., 9: 435–448

The increasing concern about the environment and the adverse effect of the chemical elements depositions on different recepient systems has lead to the development of scientifically based critical load concept. To apply critical load definition to nitrogen on arable soils, it is necessary to decide upon criteria, which should make the basis for the “qualitative estimate” of critical load for nitrogen. Here is presented a case study for assessment of critical nitrogen loads on arable Fluvisols by using a steady-state mass balance method. The basic principle of the SSMB method is to identify the long-term average fluxes of acidity and alkalinity in the system and to determine the maximum tolerable acid input that will balance the system at safe limits for the selected receptor. In the studied soil, pH values are used as criteria for soil stability and [H]/[Al] ratio as a critical chemical value associated with the risk of approaching the critical aluminium buffer range. For the determination of input-output fluxes of nitrogen and base cations and calculation critical loads were used data from long-term complex experiment on Alluvial-meadow soil (Fluvisol) with maize grown as monoculture under irrigation, conducted since 1972 till 1998. The experiment design includes five variants of fertilizer treatment in six replications. For the assessment was used steady-state mass balance equation, which describes the interaction between incoming and outgoing chemical elements. Analysis of the results show that using pH values as a criterion, considerably high critical nitrogen load of 225 kg.ha–1.yr–1 was received. This could be explained by introduction of greater amounts of neutralizing base cations through precipitation and irrigation, which has lead to the increasing of neutralizing potential of Alluvial-meadow soil, despite its low buffer range.

Key words: critical nitrogen loads, acidification, SSMB, input-output fluxes