Fungal/bacterial ratios in grasslands with contrasting nitrogen management

Abstract

It is frequently hypothesised that high soil fungal/bacterial ratios are indicative for more sustainable agricultural systems. Increased F =B ratios have been reported in extensively managed grasslands. To determine the shifts in fungal/bacterial biomass ratio as influenced by grassland management and to find relations with nitrogen leaching potential, we sampled a two-year-old field experiment at an organic experimental farm in the eastern part of The Netherlands. The effect of crop (grass and grass-clover), N application rate (0, 40, 80, 120 kg N ha À1 ) and manure type (no manure, farm yard manure and slurry) on the F=B ratio within three growing seasons was tested, as well as relations with soil and crop characteristics, nitrate leaching and partial N balance. Biomass of fungi and bacteria was calculated after direct counts using epifluorescence microscopy. Fungal and bacterial biomass and the F =B ratio were higher in grass than in grassclover. The F =B ratio decreased with increasing N application rate and multiple regression analysis revealed a negative relationship with pH. Bacterial activity (measured as incorporation of [ H]thymidine and [14 C]leucine into bacterial DNA and proteins) showed the exact opposite: an increase with N application rate and pH. Leaching increased with N application rate and was higher in grass-clover than in grass. Partial N balance was more positive at a higher N application rate and showed an inverse relationship with fungal biomass and F =B ratio. We conclude that the fungal/bacterial biomass ratio quickly responded to changes in management. Grasslands with higher N input showed lower F =B ratios. Grass-clover had a smaller fungal biomass and higher N leaching than grass. In general, a higher fungal biomass indicated a lower nitrogen leaching and a more negative partial N balance (or smaller N surplus), but more observations are needed to confirm the relationship between F =B ratio and sustainability. r

An ecosystem approach to assess soil quality in organically and conventionally managed farms in Iceland and Austria

“…Other studies also have reported a higher microbial activity Hole et al, 2005), which we did not find in our study. We did not find differences in fungal biomass, in contrast with some previous results (Yeates et al, 1997;de Vries et al, 2006), but in line with others (Shannon et al, 2002). These results might be due to the fact that added organic amendments in organic farming are generally easily degradable and therefore enhance mainly bacterial biomass and activity (Hole et al, 2005).…”

Effect of nitrogen fertilizer on nitrogen pools and soil communities under grazed pastures

“…This is higher than with other studies showing that fungi and fungal-feeding organisms are often reduced when soil N fertility and recycling increases (Coleman et al 1983;Bardgett et al 1999;De Vries et al 2006, 2007Lauber et al 2008;Krumins et al 2009). The mechanism is unknown but both are direct effects of fertilizer itself, and changes in the plant community and litter associated with fertilizers could be involved (Donnison et al 2000;Manning et al 2006).…”

The Abundance of Fungi, Bacteria and Denitrification Genes during Insect Outbreaks in Scots Pine Forests

“…Fungi and bacteria are known to respond fast to increasing organic input [11,31]. During nun moth outbreaks in pine forests, the N input via throughfall was 24% higher and 300% higher via feces and needle litter on defoliated sites during the vegetation period [25].…”