Abstract
Aims: Biological nitrification inhibition (BNI) has been reported as an emerging technology to control soil nitrifier activity for effective N-utilization in cropping systems. Brachiaria have been reported to suppress nitrifier populations by releasing nitrification inhibitors from roots through exudation. Substantial BNI activity has been reported to be present in the root tissues of Brachiaria grasses; however, BNI contribution, such as root turnover, has not been addressed in previous studies. The present study aimed to clarify the contribution of root turnover on BNI under Brachiaria cultivations and its impact on nitrifier populations. Methods: We monitored root growth, changes in ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) numbers, nitrification rate, and available nitrogen (N) content under seven germplasm lines of Brachiaria, for 18 months with seasonal profile sampling. Results: Brachiaria cultivation increased soil NH4+-N, available N, and total soil carbon levels. Though we did not find any correlation between the changes in AOB populations and potential nitrification, the potential nitrification rate decreased when AOA populations decreased. Multiple regression analysis indicated that BNI substances from root tissue turnover had a significant contribution to the BNI function in the field. Conclusion Results indicated that the inhibitory effect of BNI was mostly evident in AOA, and not in AOB, in this study. Brachiaria cvs. ‘Marandu’, ‘Mulato’, and ‘Tupy’ had the most substantial BNI effect among the seven cultivars evaluated. The estimated total BNI activities and available N content of root tissue explained the observed nitrification inhibition. In conclusion, the release of BNI substances through plant decomposition contributes to the decrease in the abundance of AOA, and thus the inhibition of nitrification under Brachiaria cultivation.
Highlights
Nitrogen (N) dynamics in agricultural soils is one of the most significant factors for crop production and environmental load from the farming sector
We noticed that the available N concentration generally increased with the plant root amount, reflecting N immobilization and root decomposition, and this outcome was supported by a significant correlation between available
Standard regression coefficients, which show the rate of contribution for the previous studies consider that biological nitrification inhibition (BNI) phenomenon was caused mostly by BNI activity release from determination, were 0.261 for BNI activity in root tissue, 0.109 for BNI activity in root exudate, and exudation [1,6,16] but our results showed that BNI released from root tissue had a significant
Summary
Results indicated that the inhibitory effect of BNI was mostly evident in AOA, and not in AOB, in this study. ‘Marandu’, ‘Mulato’, and ‘Tupy’ had the most substantial BNI effect among the seven cultivars evaluated. The estimated total BNI activities and available N content of root tissue explained the observed nitrification inhibition. The release of BNI substances through plant decomposition contributes to the decrease in the abundance of AOA, and the inhibition of nitrification under Brachiaria cultivation
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