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 UniversityCollaborator Curtis Dell, USDA-ARS Watershed Management and

Pasture Systems Research Unit, University Park, PA

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

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

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

Surface application of manures results in higher NH3 losses, while manure injection shows higher N2O losses

Dell et al. 2011.J Environ Qual

Dell et al. 2011. J Environ Qual

Two dissimilatory nitrate reduction pathways: Denitrification vsDissimilatory 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

Soil factor More conducive to DNRA

Reduced conditions YesHigher C:NO3

- YesPresence of roots Yes/NoRespirable carbon sources (glucose) YesSome fermentable carbon sources (glucose)

Yes

Other labile carbon sources (succinate) NoFormate, H2 YesAlfalfa YespH ?Soil dissolved organic matter ?

Studies on Effects of Environmental Conditions on DNRA(reviewed by Rütting et al. 2011)

Authors Primer developed Environment

Mohan et al. 2004Mohan 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 2006Takeuchi 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

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

Riparianenvironment

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

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

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

LOSSES TO WIND AND WATER

PRIMARY PRODUCTION(including roots)

HERBIVORES

CARNIVORES

DETRITUS

SAPROVORESFUNGI, BACTERIA

MACRO-FAUNAL DETRITIVORES

MICROBI-VORES

PREDATORSHUMANS

SOIL HUMUS

PRIMARY PRODUCTION

HERBIVORES

HUMANS

DETRITUS

SAPROVORESBACTERIA

MICROBI-VORES

SOIL HUMUS

Undisturbed system

High mechanical disturbanceLow-carbonFew trophic levelsConstant OM lossTemporal gradientsMostly oxic

Tilled agricultural system

Micro-scale disturbanceHigh-carbonMany trophic levelsGreater OM accumulationLittle OM lossSpatial gradientsOxic to anoxic

Take home messagesNo-till management can mitigate atmospheric CO2 by reducing soil erosion andincreasing soil carbon sequestration. As of 2010-2011, 38% of U.S. acreage in the fourmajor crops was managed with no-till or strip-till.

Under some conditions, no-till can lead to GHG tradeoff of higher emissions of morepotent N2O.

N2O is produced mainly by denitrification, one of two pathways for dissimilatorynitrate reduction. Nitrate ammonification, the second pathway, generates the lessmobile NH4

+.

Since manures contain NA bacteria, soil N could be conserved through designingcarbon and manure management practices that promote soil conditions conducive toNA.

To address GHG tradeoffs in conservation agriculture, better understanding ofdissimilatory nitrate reduction is needed through quantitative 15N tracing and Nfunctional gene analysis.

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)