Abstract
The effects of intensive nitrogen (N) fertilizations on spatial distributions of soil microbes in bioenergy croplands remain unknown. To quantify N fertilization effect on spatial heterogeneity of soil microbial biomass carbon (MBC) and N (MBN), we sampled top mineral horizon soils (0-15 cm) using a spatially explicit design within two 15-m2 plots under three fertilization treatments in two bioenergy croplands in a three-year long fertilization experiment in Middle Tennessee, USA. The three fertilization treatments were no N input (NN), low N input (LN: 84 kg N ha−1 in urea) and high N input (HN: 168 kg N ha−1 in urea). The two crops were switchgrass (SG: Panicum virgatum L.) and gamagrass (GG: Tripsacum dactyloides L.). Results showed that N fertilizations little altered central tendencies of microbial variables but relative to LN, HN significantly increased MBC and MBC:MBN (GG only). HN possessed the greatest within-plot variances except for MBN (GG only). Spatial patterns were generally evident under HN and LN plots and much less so under NN plots. Substantially contrasting spatial variations were also identified between croplands (GG > SG) and among variables (MBN, MBC:MBN > MBC). This study demonstrated that spatial heterogeneity is elevated in microbial biomass of fertilized soils likely by uneven fertilizer application in bioenergy crops.
Highlights
Strong correlation between spatial patterns of soil denitrifiers community with nitrate and other nutrients at scales relevant to land management[18]
Previous results suggest that soil microbial features such as microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) can greatly respond to fertilization in their spatial variability compared with soils without fertilizer input for years in bioenergy croplands
The distribution of MBC:MBN showed higher frequency in lower values in general, but the frequency of higher values were large for high N input (HN) than low N input (LN) for GG (Fig. 2)
Summary
Strong correlation between spatial patterns of soil denitrifiers community with nitrate and other nutrients at scales relevant to land management[18]. Spatial patterns and the scale of soil variability differ markedly among edaphically similar sites and these differences are conditioned likely by intensity and duration of fertilizations[13,14,29]. Previous results suggest that soil microbial features such as MBC and MBN can greatly respond to fertilization in their spatial variability compared with soils without fertilizer input for years in bioenergy croplands. The objective of this study is to investigate effects of N fertilization on spatial distribution of soil MBC, MBN and MBC:MBN in two bioenergy croplands (SG and GG) in a three-year long field experiment at Tennessee State University’s campus farm in Nashville TN, representing a typical bioenergy crop site in Middle Tennessee. This study is expected to clarify the fertilization effect on redevelopment of spatial heterogeneity of key soil microbial features in typical bioenergy croplands
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