|SEGAL, LAUREN - University Of Nebraska|
|LOECKE, TERRENCE - University Of Nebraska|
|Cook, Kimberly - Kim|
|SHAPIRO, CHARLES - University Of Nebraska|
|DRIJBER, RHAE - University Of Nebraska|
Submitted to: Soil and Tillage Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/28/2016
Publication Date: 1/7/2017
Publication URL: http://handle.nal.usda.gov/10113/5603520
Citation: Segal, L.M., Miller, D.N., McGhee, R., Loecke, T.D., Cook, K.L., Shapiro, C.A., Drijber, R.A. 2017. Bacterial and archaeal ammonia oxidizers respond differently to long-term tillage and fertilizer management at a continuous maize site. Soil and Tillage Research. 168:110-117.
Interpretive Summary: Fertilizer use and tillage likely affect microbial communities in complex ways. A study of soils collected at three key dates from a continuous corn site where tillage (no-till and disk) and N fertilizer rates (0, 40, 80, 120, and 160 kg ha-1 yr-1) were maintained over the long-term (26+ years). Changes in the general microbial community and in the two major groups of ammonia-oxidizing microorganisms were investigated by measuring unique biomarkers. Ammonia-oxidizing archaea (AOA) greatly outnumbered ammonia-oxidizing bacteria (AOB) and varied among sampling dates. Tillage had a differential effect; AOB were almost 10-fold lower in disk plots, but AOA did not differ. N rate had no effect on ammonia-oxidizer abundance, but a moderate correlation between AOB and N rate was observed. AOA correlated moderately with water-filled pore space. In contrast, the biomass of microbial groups within the general community was dynamic and responsive to sample date, tillage, and N rate. This study found that although long-term practices affected microbial communities, short term changes over a field season were surprisingly dynamic, particularly for the general soil community.
Technical Abstract: Fertilizer use and tillage affect both the general soil microbial community and speci'c N-utilizing microbial groups, but likely to varying degrees. To assess these impacts, soil was collected on three key dates from a long-term (26+ years), rainfed, continuous maize site where tillage (no-till and disk) and N fertilizer rates (0, 40, 80, 120, and 160 kg ha''1 yr''1) were applied. Microbial community changes were assessed using fatty acid methyl esters (FAME), and ammonia oxidizer (AO) changes were followed using quantitative PCR. Ammonia-oxidizing archaea (AOA) greatly outnumbered ammonia-oxidizing bacteria (AOB) based upon amoA gene copy (108 versus 104 g''1 soil, respectively), and both populations were dynamic across sampling dates. Over the long term, tillage had a differential effect; AOB were almost 10-fold lower in disk tillage plots, but AOA did not differ. N rate had no effect on ammonia-oxidizers abundance, but a moderate correlation (r = 0.423) between AOB and N rate was observed. AOA correlated moderately (r = 0.552) with water-'lled pore space. In contrast, the biomass of various microbial groups was highly responsive to sample date, tillage, and N rate. This study found that long-term agronomic practices affected the overall microbial community more than the AO community, while short-term changes over a growing season were surprisingly dynamic for both AO and select groups within the general soil community.