Nitrogen mineralization and nitrification in four Minnesota old fields

Abstract

Nitrogen availability and its response to fertilizer amendments was measured by in situ incubation in four old fields ranging in age from 16 to >100 years at Cedar Creek Natural History Area. Net nitrogen mineralization in control plots increased with field age, from 4.4 g/m in the youngest field to 6.5 g/m in the oldest field. The proportion of total N mineralized decreased with field age, from 6.2% of total N mineralized in the youngest field to 4.8% mineralized in the oldest field, suggesting a decrease in organic matter quality with time. Unlike many forests in the region, nitrogen mineralization was correlated with total soil nitrogen content. Greater than 90% of the mineralized N was nitrified in most months. Analyses of variance indicate significant effects of field age and month of year on N mineralization and nitrification, but not effect of fertilizer treatment except in the oldest field. Fertilizer additions did not significantly increase standing pools of mineral N in the youngest or oldest fields but did in the 26 and 50 year old fields. However, changes in mineral N pools did not account for the amount added in fertilizer. Strong plant and microbial sinks for fertilizer and possibly leaching losses may be the reasons why fertilizer additions did not stimulate N mineralizations during the first two years in most fields.

Soil nitrogen mineralization in adjacent stands of larch, pine and oak in central Korea

“…High nitrification for Larix spp was also reported from another study . Although initial soil nitrate concentration was low, net nitrification was important for the three species (Nadelhoffer et al, 1984;Pastor et al, 1987). However, there is a possibility that nitrification might be overestimated in soil incubations where root uptake of N was prevented (Zak and Grigal, 1991).…”

“…This method is widely used to investigate N cycling in different ecosystems (Nadelhoffer et al, 1983;Pastor et al, 1984Pastor et al, , 1987Gower and Son, 1992) because of its sensitivity to differences in on-site soil temperature and moisture (Binkley and Hart, 1989 . However, average nitrate concentrations were generally lower than those reported for other forest soils in temperate regions (Nadelhoffer et al, 1983;Gower and Son, 1992 Henderson, 1990a, b;Wedin and Tilman, 1990;Hart et al, 1994).…”

“…Various researchers have found that soil chemical characteristics can predict soil N mineralization (Pastor et al, 1987;Nadelhoffer et al, 1991;Zak and Grigal, 1991) (but see Nadelhoffer et al, 1983Nadelhoffer et al, , 1984Pastor et al, 1984;Gower and Son, 1992). However, there was no significant correlation (P > 0.1) between annual net N mineralization and previously measured soil organic carbon (C) concentration, total soil N concentration, soil organic matter C:N ratio or total soil N content (data from Kim, 1995).…”

“…Pastor et al (1984) also reported a correlation between litterfall N contents and N mineralization (but see Gower and Son, 1992 (Aber and Melillo, 1982;Pastor et al, 1987;Wedin and Tilman, 1990;Gower and Son, 1992;Stump and Binkley, 1993;Garten and Van Miegroet, 1994), more detailed studies are necessary to clarify the major factors of regulating soil N mineralization in this forest ecosystem.…”

Changes in Nitrogen Mineralization, Tissue Nutrient Concentrations and Biomass Compartmentation after Cessation of Fertilizer Application to Mown Grassland

“…The dependence on substrate makes the mineralization rate not only a determinant of the species composition of the vegetation, but also dependent on this factor, since large differences between plant species exist in the amount and chemical composition of the flow of plant organic matter to the soil (Vitousek & Walker 1987;Berendse et al 1989;Wedin & Tilman 1990). Because high N addition rates can decrease tissue C/N ratios leading to lower decomposition rates (Pastor et al 1987;Berendse & Elberse 1989) the N mineralization rate probably increased during the period of intensive agricultural use. Stopping the application of fertilizers would then lead to an only partially reduced N availability, since the high mineralization rates would be expected to continue until the 'high quality' organic matter was used up.…”