The contribution of nitrogen through microbial biomass to plant nitrogen uptake in upland soils with different physiochemical properties.

摘要

The contribution of N through microbial biomass to plant N uptake was investigated in a light-coloured Andosol, Humic Andosol, brown lowland soil (Fluvisol), dark red soil and a sand-dune Regosol by labelling microbial biomass N with 15N. At 3 weeksafter amendment, upland rice was sown and cultivated in 15 weeks. Soil and plant samples were taken at every 3 weeks after sowing (WAS). The results showed: (1) soil microbial biomass N amounts were in the order: dark red soil > Humic Andosol > brown lowland soil > light-coloured Andosol > sand-dune Regosol. Microbial biomass N in all soils was almost constant during the cropping period; (2) plant N uptake was in the order: brown lowland soil > Humic Andosol > dark red soil > light-coloured Andosol > sand-dune Regosol. Plant N uptake in all soils was greatest in the heading stage, suggesting that the N uptake is high in the reproductive stage; (3) At 0-3 WAS, the 15N abundance of plant N uptake in all soils was close to that of the microbial biomass N. At 6-15 WAS, however, it was close to that of soil total N. It is assumed that the N taken up by the plant is mainly derived from the N produced through the microbial biomass in the vegetative growth stage (0-6 WAS), and mainly from organic N except for the microbial biomass N in the reproductive stage (6-15 WAS); and (4) except for the dark red soil, plant N uptake was closely correlated with microbial biomass N at the vegetative growth stage (R=0.995, n = 4), showing that microbial biomass N is a major source of N for plants at this stage.