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Cover crops (CC) have demonstrated beneficial effects on several soil properties yet questions remain regarding their effects on soil microbial communities. Among them, ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) have a key role for N cycling in soil and their responses in the rhizosphere of terminated CC deserve further investigation. A greenhouse experiment was established to assess N fertilization (with or without N) and termination methods (glyphosate, mowing, and untreated control) of common oat (Avena sativa L.) as potential drivers of AOA and AOB responses in the rhizosphere. The abundance of amoA genes was determined by quantitative real-time PCR (qPCR), the community structure was assessed with Illumina amplicon sequencing of these genes, while the function was assessed from potential nitrification activity (PNA). While N fertilization had no influence on AOA, the termination method significantly increased amoA gene copies of AOA in mowed plants relative to glyphosate termination or the untreated control (1.76 and 1.49-fold change, respectively), and shifted AOA community structure (PERMANOVA, p <0.05). Ordination methods indicated a separation between AOA communities from control and glyphosate-terminated plants relative to mowed plants for both UniFrac and Aitchison distance. Converserly, N fertilization significantly increased AOB abundance in the rhizosphere of mowed and control plants, yet not in glyphosate-treated plants. Analyses of community structure showed that AOB changed only in response to N fertilization and not to the termination method. In line with these results, significantly higher PNA values were measured in all fertilized samples, regardless of the termination methods. Overall, the results of this study indicated that bacterial and archaeal nitrifiers have contrasting responses to fertlization and plant termination methods. While AOA were responsive to the termination method, AOB were more sensitive to N additions, although, the stimulative effect of N fertilization on amoA AOB abundance was dependent on the termination method. [ABSTRACT FROM AUTHOR]

Cover crops (CC) are being actively promoted in Illinois as a tool to improve soil properties and enhance crop performance and yield. Our goals were to assess the short-term ability of radish (Raphanus sativus L. var. longipinnatus) and companion CC to improve (i) soil properties and (ii) soybean (Glycine max L. Merr.) growth and yield following compaction and CC treatments under conventional systems. We used a 6 X 3 factorial arrangement of the CC and compaction treatments in a completely randomized design with two replications in two independent year-locations hereby referred as environments. Cover crop treatments included radish alone "R", and with rye (Secale cereale L.) "RR", triticale (x Triticosecale 'Presto') "RTR", buckwheat (Fagopyrum esculentum L. Moench) "RB", or hairy vetch (Vicia villosa Roth) "RH V", and a control with no cover crop "NCOV". Compaction treatments were no compaction (Nc), and two levels of compaction achieved with a large tractor (LT) or a hauling truck (TK). Compaction was temporarily achieved and disappeared after the CC growing season. Cover crop treatments significantly lowered soil NO3-N compared to NCOV yet no further effect was evident on soils. Soybean yield for CC treatments were not different from control plots. Results from this study showed that one growing season was not enough time to evidence changes in soil properties related to cover cropping yet they were useful tools for retaining NO3-N in the system. In addition, following adequate management practices, CC should not affect soybean growth and yield. [ABSTRACT FROM AUTHOR]