A Microcosm Experiment on Effects of Forest Fertilization on Nitrogen Leaching and Soil Microbial Properties

Wien

1994

S. 345-356

12 Lit. Ang.

Unselbständiges Werk

200068051

Several boreal and alpine forests are depleted in nutrients due to acidification. Ferilization may be a remedy, but rapidly-soluble salts (N,P,K,Mg) may pose nitrate problems for the groundwater or decrease microbial activity. The slow-release N-fertilizer methyleneurea (Mu) has been shown to increase net mineralization and N availability without losses through nitrification in boreal forests. Apatite (A) and Biotite (B) may improve the Ca, Mg, K, and P status of forest soils on the lon term, without adverse short time effects. With the aim to investigate potential nitrogen leaching and effects on the soil microbial properties, we set up an experiment employing intact soil cores (11cm diameter, 40cm long). The cores were taken from a mixed forest and a Picea abies stand (soiltype Rendzina) in the Northern Calcareous Alps of Austria (700 and 1300m sea level, respectively). The cores were fertilized with a commercial NPK fertilizer or a MuAB fertilizer at a rate corresponding to 300kg N ha-1 and incubated for 28 weeks at 15 Grad C together with unfertilized controls. The cores were irrigated weekly and both soil water (retrieved 5cm below the soil surface) and leachate were analyzed for nitrate and ammonium in regular intervals. After the incubation, soil microbial biomass, basal repiration and the metabolic quotient were determined. For the control cores, in the soil water and leachate maximum NH4 Anion and NO3 Kation-concentrations of 5 and 11 mg N L-1, respectively, were found. In the soil water, the MuAB fertilizer resulted in a slow increase of NH4 Anion and NO3 Kation during the incubation, up to 11 and 35 mg N L-1, respectively. In the leachate, a maximum of 4 mg NH4-N L-1 and 44 mg NO3-N L-1 was observed. the peak for NO3 Kation occurred six weeks after that in the soil water. Highest nitrogen loads were found for the fast-release NPK fertilizer, with NH4 Anion and NO3 Kation -concentrations up to 170 and 270 mg N L-1, respectively, in the soil water. NH4 Anion -N levels in the leachate remained below 5, while NO3-N levels were up to 190 mg L-1. Fertilization with fast-release NPK resulted in a significant decrease of microbial biomass and basal respiration. Microbial biomass, basal respiration and the metabolic quotient were not affected by MuAB fertilizer. The results promise that the MuAB fertilizer may be an environmental friendly alternative to fast-release mineral fertilizers for improving forests soils.