Date post: | 13-Apr-2017 |
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Environment |
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Grazing Management Effect on Micro- and Macro-Scale Fate of C and N in Rangelands
M. Mamo, J. Bradshaw, K. Evans**, K. Eskridge, R. Ferguson, J. Guretzky, K Jenkins, A. Sanford**,
W. Schacht, J. Volesky, P. Wagner**, A. Wingeyer, H. Yang
Outline• Background• Project Scope• Objectives• Site Description• Result-highlights• Summary• Accomplishments
Grazing Management StrategiesLow stocking density Ultra high stocking density10 steers for 27 days in both pastures = same stocking rate
Proposed advantages of ultra high stocking density (MOB)
• Increased SOM• Increased pasture productivity• Increased species diversity• Increased dung beetle activities• Uniform fecal & urine deposition• Increased animal production per area
Project Scope
Questions• Are the rates of decomposition and/or
incorporation of nutrient pulses under specific grazing strategies regulated by the spatial and temporal distribution of these pulses?• How do these affect nutrient cycling and
nutrient use efficiency?• What are the levels of association of grazing
strategies to pattern of nutrient return and soil nutrient availability
Project Scope cont…
Plant pool
CowPool
ExcretaPool
Soilpool
Spatially coupled nutrient cycling
Plant pool
CowPool
ExcretaPool
Soilpool
Spatially un-coupled nutrient cycling
Project Objectives
a) Size of pulsesa) Dungb) Litterc) Urine
b) Pattern of returnc) Pattern of dung
beetles
C &N pulses in relation to grazing strategies
d) Decomposition, transport & transformations of C & N
e) Relationships of grazing/pulses/beetles/nutrient fatef) Pasture level estimations of nutrient cyling
UpscalingFate of dung C &N
Two MSc. students
MSc. student
PhD student
Site Description• The Barta Brothers Ranch
– 2100 ha in Eastern Sandhills• 2000 ha of upland range• 100 ha of meadows
– 560 mm annual precipitation– 75% during growing season
• Other collaborating ranches
Experiment Design• Grazing: May – August (60-80 d)• Stocking Rate:7.5 animal unit
months ha-1
• Low stocking density: • 7000 kg ha-1
• 10-15 d pasture-1
• Ultra high stocking density: • 225,000 kg ha-1
• 0.5 d pasture-1
Litter Deposition Rate
• Higher % trampling in MOB• No difference in litter deposition• Highest litter deposition duringgrazing season
Miles Redden, MSc. thesis, UNL, 2014
Trampled plant biomass
Low stocking
High stocking
Dung beetle frequency and diversity
• Higher dung beetle diversity in rotational grazing• 22 different dung beetle species across ranch sites
High stockingLow stocking 4PR1Low stocking 4PR2ContinuousHay
Patrick Wagner, MSc. thesis, UNL, 2016
Fate of dung C & NQuantify the fate of nutrients from decomposing dung pats with and without dung beetles– Two treatment:
• No beetle (i.e., with mesh)• With beetle (i.e., no mesh)
– Two seasonal exps each in 2014 & 2015• June • July• Soil and GHG sampling times: 1, 3, 7, 14, 28 and 56 d.
(Bertone et al., 2006)
• 4 Seasonal Experiments with 8 Rep– Exposed dung pats– Unexposed dung pats with 1 mm mesh exclosure– No dung pat
Unexposed
No dung
Exposed
Fate of dung C & N
CO2 Flux
0
500
1000
1500
2000
2500
Exposed Unexposed No Dung
CO2(g∙m
‐2)
Treatment
Cumulative Flux
• Greater flux from exposed compared to unexposed treatments observed only in 1 out of 4 experiments
• Greater flux from dung compared to no dung in 3 out of four seasonal experiments
• VWC, and [O2], significant across all seasonal experiments
0
10
20
30
40
50
60
0 10 20 30 40 50 60
CO2 Flux (g
∙m‐2∙d
‐1)
Days After Dung Placement
Early SeasonNo Beetle
Beetle
Control
0
10
20
30
40
50
60
0 10 20 30 40 50 60
CO2 Flux (g
∙m‐2∙d
‐1)
Days After Dung Placement
Late SeasonNo Beetle
Beetle
Control
Kenneth Evans, MSc. thesis, UNL, 2016
Dung Decomposition
wet dryDung moisture
Hypothesis:Speed of dung decomposition
200
220
240
260
280
300
320
340
0 10 20 30 40 50 60
Dry Matter (g)
Days After Dung Pat Placement
No Beetle
Beetle
S=0.57
S=0.62
• No differences in DM loss• Speed of aging (S) similar
DK C&N model (Yang & Janssen, 2000)
Spatial & temporal distributionMSc. student (Amanda Sanford)• Dung pat distribution in
time & space• Dung spectral
characteristics• Dung C&N estimation
Phd. student (modelling)• Integration• Relationships of
management to pulses
Summary• Greater vegetation trampling in high density grazing,
however, – No different in litter deposition– Biomass production
• High diversity of beetle in rotation grazing regardless of stocking density
• Dung beetle effect was not significant on GHG fluxes and dung decomposition
• Spatial and temporal patterns of dung distribution will be used to estimate ranch level nutrient cycling-integrating field observations and process models
Accomplishments Postdoc Graduate*
studentsUndergraduate students
Field/labsupport staff
1 3 MSc1 PhD
(2 females/2
males)
10 (5 females/5 males)
4
• Manuscripts in Prep.: 4• Manuscripts planned: 3• Symposium ASA-SSSA-CSA-ESA 2015• Field day 2015• Stakeholder workshop- 2014• Evans & Wagner (MSc)-high placementin graduate student poster competition
This project is supported by Agriculture and Food Research Initiative Competitive Grant Program no. 2013-67019-21394 from the USDA National Institute of Food and Agriculture