Greenhouse gas trade-offs and N cycling in low-disturbance soils with long term manure additions

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Published on December 23, 2016



1. Greenhouse Gas Trade-offs and N Cycling in Low- Disturbance Soils with Long Term Manure Additions Mary Ann Bruns1 and Arnab Bhowmik2 PI1 and Postdoctoral Associate 2 Co-PIs Heather Karsten and John M Regan, The Pennsylvania State University Collaborator Curtis Dell, USDA-ARS Watershed Management and Pasture Systems Research Unit, University Park, PA

2. Adoption of no-till and cover cropping varies widely by crop and region (USDA Economic Research Service, 2015)

3. Sustainable Dairy Cropping Systems (SDCS) study funded by Northeast-SARE, Penn State, and USDA-ARS • Initiated in 2010 • Scale model of 240-acre dairy farm • No-till rotations of feed, forage, fuel • Measuring yield and quality to model production from virtual herd Goals • Assess management for improved sustainability • Minimize off-farm inputs • Reduce environmental impacts

4. Broadcast In conjunction with cover cropping, SDCS study compares two dairy manure application methods: • Broadcast • Injected with shallow disk Benefits of injection: • Reduced NH3 volatilization • Greater nutrient availability to crops

5. Surface application of manures results in higher NH3 losses, while manure injection shows higher N2O losses Dell et al. 2011. J Environ Qual

6. Dell et al. 2011. J Environ Qual

7. Two dissimilatory nitrate reduction pathways: Denitrification vs Dissimilatory Nitrate Reduction to Ammonium (DNRA) Although both processes are known to occur, only one (denitrification) has been thought to account for nearly all nitrate dissimilation in agricultural soils Two-step process in DNRA (aka nitrate ammonification (NA) • Reduction of nitrate to nitrite (nitrate respiration) • Reduction of nitrite to ammonium (fermentation) Overall reaction: NO3 − + 4H2 + 4H+ → NH4 + + 3H2O

8. Soil factor More conducive to DNRA Reduced conditions Yes Higher C:NO3 - Yes Presence of roots Yes/No Respirable carbon sources (glucose) Yes Some fermentable carbon sources (glucose) Yes Other labile carbon sources (succinate) No Formate, H2 Yes Alfalfa Yes pH ? Soil dissolved organic matter ? Studies on Effects of Environmental Conditions on DNRA (reviewed by Rütting et al. 2011)

9. Authors Primer developed Environment Mohan et al. 2004 Mohan et al 2004 (490 bp) Anammox reactor Smith et al. 2007; Dong et al. 2009; Lam et al. 2009 Estuarine sedimentsLam et al. 2009; Takeuchi 2006 Takeuchi 2006 Smith et al. 2007; Papaspyrou et al. 2014; Smith et al. 2015 Smith et al 2007 Welsh et al. 2014; Song et al. 2014; Decleyre et al. 2015; Zheung et al. 2016 Welsh et al 2014 (259 bp) Agricultural soil and estuarine sediments Reported primer sets used to amplify nrfA gene responsible for DNRA

10. Summary of current NA research and determined rates in different ecosystems Ecosystem NA rate (µg N g-1 soil day-1) NA:NO3 - consumption (%) No. of studies Riparian environment 0.36-1.3 2.8 2 Temperate forest 0.004-1.0 0.4-100 7 Sub-tropical forest 0.015-0.053 2.1-15.6 2 Tropical forest 0.03-2.89 2.2-100 6 Temperate grassland 0.034-0.27 0.6-97 6 Arable field 0-0.3 0-6.3 1 Adapted from Rutting et al. (2011) Biogeosciences 8 (7): 1779

11. 300 250 (bp) AerobicAnoxicAnaerobic Core hypothesis: NA activity is responsive to soil conditions, which are in turn driven by soil management. Preliminary nrfA-PCR results for genomic DNA and reverse- transcribed mRNA from sludges at different locations of wastewater treatment plant

12. Neighbor-joining phylogenetic tree of nrfA amino acid sequences. Taxa in red have been shown to reduce nitrite to ammonium in culture. Kashima et al. in preparation

13. LOSSES TO WIND AND WATER PRIMARY PRODUCTION (including roots) HERBIVORES CARNIVORES DETRITUS SAPROVORES FUNGI, BACTERIA MACRO-FAUNAL DETRITIVORES MICROBI- VORES PREDATORSHUMANS SOIL HUMUS PRIMARY PRODUCTION HERBIVORES HUMANS DETRITUS SAPROVORES BACTERIA MICROBI- VORES SOIL HUMUS Undisturbed system High mechanical disturbance Low-carbon Few trophic levels Constant OM loss Temporal gradients Mostly oxic Tilled agricultural system Micro-scale disturbance High-carbon Many trophic levels Greater OM accumulation Little OM loss Spatial gradients Oxic to anoxic

14. Take home messages No-till management can mitigate atmospheric CO2 by reducing soil erosion and increasing soil carbon sequestration. As of 2010-2011, 38% of U.S. acreage in the four major crops was managed with no-till or strip-till. Under some conditions, no-till can lead to GHG tradeoff of higher emissions of more potent N2O. N2O is produced mainly by denitrification, one of two pathways for dissimilatory nitrate reduction. Nitrate ammonification, the second pathway, generates the less mobile NH4 +. Since manures contain NA bacteria, soil N could be conserved through designing carbon and manure management practices that promote soil conditions conducive to NA. To address GHG tradeoffs in conservation agriculture, better understanding of dissimilatory nitrate reduction is needed through quantitative 15N tracing and N functional gene analysis.

15. PSU Agronomy Farm, Rock Springs, Centre County Support provided by USDA-NIFA and a seed grant from PSU Institutes of Energy and the Environment (IEE) 2015/2016 to fund preliminary work by Dr. Hiroyuki Kashima Acknowledgements Award # 2016-67003-24966 We also acknowledge the USDA-NESARE Program support of Penn State’s Sustainable Dairy Cropping Systems project, 2009-2016, and collaboration with the Sustainable Dairy Coordinated Agricultural Project (Dairy CAP)

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