A study was carried out to investigate the effects

of different diets for heifers, low- and high-yielding cows on

the microbial composition of their faeces and subsequently

the impacts of these faeces on CO

2

and N

2

O emissions, N

mineralisation and plant N uptake. A diet low in N and high

in acid detergent fibre offered to heifers resulted in faeces

dominated by fungi. These faeces were characterised by a

low content in microbial biomass C and N and a high

ergosterol concentration in comparison to the faeces of

high-yielding cows. Added to soil, faeces of heifers led to

lower emission and stronger N immobilisation during a 14-

day incubation in comparison to the faeces of high-yielding

cows. Total N

2

O emission was significantly (

P

<0.05) cor-

related with faecal microbial biomass N. Rye grass yield and

N uptake were lowest in the soil supplemented with faeces

from heifers in a 62-day pot experiment. Plant N uptake was

influenced by the faecal microbial biomass C/N ratio and the

fungal C to bacterial C ratio. In conclusion, the faecal

microbial biomass was affected to a high degree by the

feeding regime and faecal microbial characteristics revealed

higher impacts on plant N uptake than soil microbial

properties.