Seasonal dynamics of arginine ammonification in forest soils of Norway spruce pure stands under different silvicultural practices

Effects of seasonal dynamics and silvicultural practice on ammonification of arginine, one of the proteinogenic amino acids, were assessed in surface organic H-horizon of three Norway spruce pure stands in medium altitudes (600 - 660 m a.s.l.). Contents of ammonium ions NH4+measured monthly in the field and contents of NH4+after laboratory incubation of these samples with arginine were taken as dependent variables in ANOVA and in linear regression model using generalised linear model. The aim of the analyses was to determine the significance of decomposition of this amino acid in H-horizon of forest soils and to determine categorical and continuous predictors which influence intensity of the ammonification. Laboratory experiments confirmed its close link to seasonal dynamics, as well as to forest management; however the last mentioned was firstly found as less significant when compared within whole season. As regards to seasonal dynamics in forest soils, the highest amount of ammonium ion was released in May and the lowest in July. As regards to the silvicultural practice applied, more ammonium ion was released under mature spruce monoculture, especially in August and May; in the young stands, the method of thinning had no effect on the ammonium ion release. However, the arginine ammonification was found to be influenced by ammonium nitrogen content (slight, less significant negative correlation) and by soil water content (stronger positive significance), especially in the stand with thinning from below. This was concluded to be caused by changes in stand microclimate in function of the silvicultural practice.

The determination of potential ammonification in soil by arginine method

In this paper investigations were carried out on two soil types (vertisol and brown forest soil) with different doses of applied N-fertilizer: diameter, N60 N90; N120 and N250. The potential ammonification in soil was obtained by arginine method. The following properties of soil were determined: pH value organic C, available NH4-N and mobile-Al. The pH value in vertisol was 3.75-4.07; mobile-Al was 0.67-4.90 mg/100g; % organic C 1.38-1.46 and the content of available nitrogen was 4.4-11.2 ppm. The amount of released NH4-N by arginine ammonification in this soil type was very low [(-0.12)-0.27mg/g-1h-1]. Correlation coefficients between released NH4-N from arginine and soil pH were (-0.96*), mobile Al - (-0.99**), applied fertilizer doses - (-0.95*). In brown forest soil the amount of released NH4-N by arginine ammonification was greater than in vertisol, ranging from 3.16 to 7.11mg/g-1h-1. Correlation coefficients between soil properties and released NH4-N from arginine were not statistically significant.

Effet de l’herbicide atrazine sur la respiration et l’ammonification de l’azote organique dans un sol agricole au cours d’une incubation

The importance of soil microflora and fauna in the breakdown of organic matter and nutrient release for plant growth is well recognized. However, the use of pesticides can affect soil bioactivity in a variety of ways. A long-term incubation laboratory experiment was performed to study the impact of the herbicide atrazine (commercial formulation) on soil respiration and arginine ammonification. The incubation time was lower than the half-life time for atrazine: this allows the presence of significant amounts of residual atrazine in soil throughout the incubation period. Atrazine induced a marked stimulation of cumulative CO2 evolution and the results were analyzed to fit a first-order degradation model for soil organic carbon. In the presence of various atrazine application rates (from 1 to 5 times the agricultural rate), the soil mineralizable carbon content was found to be 1.7 and 1.4 times higher than that of untreated soil. During the incubation, a marked temporal variability occurred in the arginine ammonification rate. Atrazine induced a decrease in ammonification rate, in comparison to the one obtained for the untreated soil. The ammonification rate varied little for atrazine applications greater than three times the agricultural rate, and for incubation times greater than 40 d. The characterization of the relation between the soil CO2 production rate (for 1 or 2 wk) and the ammonification rate (for 3 h) was obtained as a function of incubation time intervals by applying linear regression functions. Results showed that these variables are not significantly related. Key words: Bioactivity, atrazine, respiration, arginine ammonification, agricultural soil