Distinct interaction between management history and nitrogen source drive microbial nitrogen processes in soil

Microbial processes in soil primarily govern nitrogen (N) availability to plants. However, microbial processes can
be altered by farming history due in part to resource adaptation by microbes and such changes could further
modify N dynamics between fertiliser and plants. Here, using a two-months greenhouse experiment, we investigated
plant N uptake from applied fertilisers as well as microbial parameters in N cycling modified by management
history and fertiliser types. Sixteen soils were collected from either organically or conventionally
managed fields and fertilised with (15NH4)2SO4 (mineral N fertiliser) or 15N-Lolium multiflorum (organic N fertiliser).
Among microbial parameters tested, ammonia-oxidizing archaea (amoA) and membrane-bound nitrate
reductase (narG) gene abundance responded to management × fertiliser interaction. Organically managed soils
exhibited greater gene abundances with organic fertiliser compared to mineral fertiliser, and the opposite trend
was observed with conventional management and mineral fertiliser. Plant fertiliser N uptake was associated with
all microbial parameters tested, however, no positive interactions between management history and fertiliser
type was observed. A clear management × fertiliser interaction effect was found exclusively in microbial biomass
N with mineral fertiliser application where its association with plant N uptake was negative with organically
managed soil but positive with conventionally manged soil at first harvest. Our results suggested that soil microbes
are highly versatile and respond strongly to current nutrients conditions. Thus, fertiliser type and timing
would be a key driver of short-term plant N uptake and warrant consideration to improve plant N recovery.