Fütterungsbedingte mikrobielle Zusammensetzung von Rinderkot ...

6. Effect of cattle faeces with different microbial biomass content on soil properties, gaseous
emissions and plant growth 75
chromatography/mass spectrometry also failed to give clear further information on the
chemical reasons for the poor availability of faecal organic N to soil microorganisms
and consequently to plants (Bosshard et al., 2011). The authors assumed that some N
compounds present in plants were not digested in the gut, and that also some excreted
recalcitrant N compounds were de novo synthesized by gut microorganisms. An N
fixation capacity like in the present cattle faeces has been observed for highly
decomposed sugarcane filter pressmud, which led to N immobilisation even at an initial
C/N ratio of 12 (Rasul et al., 2008). In the long-term, N from immobilising faeces was
also released by the microbial decomposition processes into the soil solution (Morvan
and Nicolardot, 2009; Peters and Jensen, 2011) and taken up by plants (Chadwick et al.,
2000).
N uptake by rye grass increased with faecal N concentration and decreased with
higher faecal crude fibre content. Plant N uptake decreased also with a higher fungal C
to bacterial C ratio and a higher microbial biomass C/N ratio. A negative relationship
between diet composition, faecal N concentration and N mineralisation has been
repeatedly observed for sheep faeces (Kyvsgaard et al., 2000), but also cattle faeces
(Sørensen et al., 2003; Wu and Powell, 2007; Morvan and Nicolardot, 2009). However,
none of these investigations considered the microbial quality of faeces. A rare and
interesting exception was the study of van Vliet et al. (2007), which was focussed on
faecal bacteria. Nevertheless, closer relationships have been observed between plant N
uptake and faecal microbial properties than of plant N uptake and soil microbial
properties. The microbial biomass C/N ratio and the fungal C to bacterial C ratio in
cattle faeces had a strong negative impact on plant N uptake. Highest CO2 evolution and
lowest N immobilisation suggest a stronger turnover of the microbial biomass in the
faeces treatment with high N and NE concentration and low ADF concentration. The
increased microbial turnover might be the reason why the increase in microbial biomass
did not consistently differ between the three faeces types. The relationships between
faecal and soil processes might be masked by the autochthonous microbial community.
The use of 13 C and 15 N labelled cattle faeces would make it possible to test these
assumptions using an identical approach to that presented in this study (Sørensen and
Jensen, 1998; Jensen et al., 1999; Bosshard et al, 2011; Wachendorf and Joergensen,
2011). Hence, it would be possible to investigate wether microbially incorporated C or
N derive from faeces or soil.