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Nitrogen losses from two grassland soils with different fungal biomass.

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<mark>Journal publication date</mark>05/2011
<mark>Journal</mark>Soil Biology and Biochemistry
Issue number5
Volume43
Number of pages9
Pages (from-to)997-1005
Publication StatusPublished
<mark>Original language</mark>English

Abstract

Nitrogen losses from agricultural grasslands cause eutrophication of ground- and surface water and contribute to global warming and atmospheric pollution. It is widely assumed that soils with a higher fungal biomass have lower N losses, but this relationship has never been experimentally confirmed. With the increased attention for soil-based ecosystem services and sustainable management of soils, such a relationship would be relevant for agricultural management. Here we present a first attempt to test this relationship experimentally . We used intact soil columns from two plots from a field experiment that had consistent differences in fungal biomass (68 ± 8 vs. 111 ± 9 μg C g-1) as a result of different fertilizer history (80 vs. 40 kg N ha-1 y-1 as farm yard manure), while other soil properties were very similar. In the greenhouse, the columns received either mineral fertilizer N or no N (control). We measured N leaching, N2O emissions and denitrification from the columns during 4 weeks, after which we analyzed fungal and bacterial biomass and soil N pools. We found that N2O emission and denitrification were lower in the high fungal biomass soil, irrespective of the addition of fertilizer N. After fertilizer addition, N leaching in low fungal biomass soil showed a 3-fold increase compared to the control (11.9 ± 1.0 and 3.9 ± 1.0 kg N ha-1, respectively), but did not increase in high fungal biomass soil (6.4 ± 0.9 after N addition vs. 4.5 ± 0.8 kg N ha-1 in the control). Thus, in the high fungal biomass soil more N was immobilized. An additional experiment with 15N–labelled mineral fertilizer, showed a 2-fold higher immobilization of 15N into microbial biomass in the high fungal biomass soil. However, only 3% of total 15N was found in the microbial biomass 2 weeks after the mineral fertilization. Most of the recovered 15N was in the plants (approximately 25%) or in the soil organic matter (approximately 15%). Our main experiment confirmed the assumption of lower N losses in a soil with higher fungal biomass. The additional 15N experiment showed that higher fungal biomass is probably not the direct cause of higher N immobilization, but rather the result of low nitrogen availability. Both experiments confirmed that higher fungal biomass can be considered as an indicator of higher nutrient retention in soils.