Effects of agricultural land management on soil denitrification: A meta-analysis

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Amy Wiedenfeld, University of Florida, Davie, FL, Yuxi Guo, School of Forest Resources and Conservation, University of Florida, Fort Lauderdale, FL, Bei Huang, School of Life Sciences, Sun Yat-sen University, Guangzhou, FL, China, Hui Zhao, School of Forest Resources and Conservation, University of Florida, Davie, FL, Benjamin Blanco Pinto, Miami-Dade College, Miami, FL and Jiangxiao Qiu, School of Forest Resources & Conservation, University of Florida, Gainesville, FL

Background/Question/Methods
Grassland ecosystems sustain a variety of ecosystem services. However, land management in grasslands can influence key ecosystem processes such as soil denitrification –the removal of nitrate from an ecosystem – that underpins multiple grassland ecosystem services. The rate of denitrification can be altered by different types of land management, such as grazing or irrigation, or different levels of management intensity. Yet few studies have taken a synthetic approach to investigate the magnitude and types of land use management on denitrification in grasslands, and what factors may explain the variation. Hence, in this study, a meta-analysis was conducted to examine how land management drives denitrification in grasslands and agricultural lands. Following a literature search on Web of Science, 2660 papers were initially identified and based on a series of filtering criteria, a final list of 180 studies were selected for data extraction (e.g., denitrification metric, land management, spatial and temporal scales, soil covariates, etc.). Studies were categorized into land management types (e.g., fertilizer, grazing), and intensity of management into low, medium, and high categories. Effect sizes (log response ratios) were estimated between intensity levels within one land management type to quantify effects of land management.
Results/Conclusions
Preliminary results showed that across all included studies, land-use intensity exerted significant effects on the rate of denitrification. Specifically, increased fertilizer use on croplands and managed grasslands led to increased denitrification, with significant differences between both low-medium category (effect size of 0.44; p<0.05) and low-high category (effect size of 0.73; p<0.05). Differences between medium and high fertilizer treatment were marginally significant (effect size of 0.40; p=0.08) due to small sample size. In addition, our initial analyses also revealed no significant effects across different categories of grazing intensity on soil denitrification (all p>0.05 for low-medium, medium-high, and low-high intensity categories). Further analyses will be conducted to investigate effect of other land management types, including irrigation and tillage, on denitrification, and whether the effects are mediated by other biotic and abiotic factors. These results will have implications on how land use could affect ecosystem services underlined by denitrification, such as water quality and greenhouse gas emissions.