The quantity of grass-root exudates varies by season, suggesting temporal shifts in soil microbial community composition and activity across a growing season. We hypothesized that bacterial community and nitrogen cycle-associated prokaryotic gene expressions shift across three phases of the growing season. To test this hypothesis, we quantified gene and transcript copy number of nitrogen fixation (nifH), ammonia oxidation (amoA, hao, nxrB), denitrification (narG, napA, nirK, nirS, norB, nosZ), dissimilatory nitrate reduction to ammonia (nrfA), and anaerobic ammonium oxidation (hzs, hdh) using the pre-optimized Nitrogen Cycle Evaluation (NiCE) chip. Bacterial community composition was characterized using V3-V4 of the 16S rRNA gene, and PICRUSt2 was used to draw out functional inferences. Surprisingly, the nitrogen cycle genes and transcript quantities were largely stable and unresponsive to seasonal changes. We found that genes and transcripts related to ammonia oxidation and denitrification were different for only one or two time points across the seasons (p < 0.05). However, overall, the nitrogen cycling genes did not show drastic variations. Similarly, the bacterial community also did not vary across the seasons. In contrast, the predicted functional potential was slightly low for May and remained constant for other months. Moreover, soil chemical properties showed a seasonal pattern only for nitrate and ammonium concentrations, while ammonia oxidation and denitrification transcripts were strongly correlated with each other. Hence, the results refuted our assumptions, showing stability in N cycling and bacterial community across growing seasons in a natural grassland.

Controlled-release Nitrogen Fertilizers (CRNFs) are an effective fertilization technique by minimizing nutrient loss and making Nitrogen (N) available to plants as they grow. Biochar-based CRNF (BCRNF) technologies have been demonstrated very promising in increase of corn yield. Despite the beneficial effects of BCRNFs, their impacts on prokaryotic and fungal soil communities are not well evaluated. Different formulations of BCRNF were developed to investigate their effects on corn productivity. We analyzed the soil microbes and their functional potential under different BCRNF regimes using amplified V3–V4 region of 16s rRNA for determining prokaryotic, and ITS genes for fungal communities. The soil prokaryotic diversity was similar across the treatments, with differences in prokaryotic genera with relative abundance of 0.1% or less in the soil (p < 0.05). In contrast, the fungal community diversity was different only for unfertilized soil. It had a high relative abundance for Aspergillus. Genus level comparison showed that Pseudofabraea was higher in Bioasphalt-based BCRNF compared to other treatments. Moreover, the N-fixing communities in soil were also similar across the treatments. At genus level, Microvirga, Azospirillum, and Methyloprofundus were highest in no-fertilizer control. The functional potential predictions using PICRUSt2 portrayed a consistent N-cycling functions across the treatments. However, the predicted gene functions related to nitrous-oxide reductase (nosZ) and hydroxylamine reductase (hcp) were significantly lower in soil receiving BCRNF containing biosolid. Overall, BCRNF treatments previously identified to increase corn yield displayed minimal shifts in the soil microbial communities. Thus, such novel fertilization would enable increased crop yield without affecting soil communities leading to sustainable crop production.