10/10/10 Summary of the Nitrogen and Carbon Cycle
on Georgia’s Pasture-Based Dairies
Outline
Nitrogen: The most mobile of plant nutrients
Why are we concerned with N?
What research are we conducting?
Interpretation of results.
N.S. Hill, Professor
Dept. Crop and Soil Sci., UGA, Athens
Carbon: Can pasture-based dairies sequester
carbon?
Are there practical benefits beyond
removing Ghg from atmosphere?
WHAT ARE THE SOIL CHEMICAL PROPERTIES THAT
MAKE NITRATE LEACHING OF SUCH CONCERN?
WHAT ARE THE SOIL CHEMICAL PROPERTIES THAT
MAKE NITRATE LEACHING OF SUCH CONCERN?
CONSIDER SURFACE CHARGES ON SOIL PARTICLES _
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K+ _
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WHAT ARE THE SOIL CHEMICAL PROPERTIES THAT
MAKE NITRATE LEACHING OF SUCH CONCERN?
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NO3-­‐ _
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NO3-­‐ K+ _
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NO3-­‐ _
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NO3-­‐ NO3-­‐ _
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NH3 NH3 _
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Groundwater NO3 levels considered safe: 10 ppm (= 10 mg NO3 L-1)
1 10/10/10 Soil water-NO3-N (ppm) from cropped land to which dairy
effluent was applied. Application strategy changed in 1998 to
accommodate nutrient demand by forage crops. (ASAE 2001:1-9.)
WHAT HAPPENS TO N WHEN LAND IS MANAGED USING
HIGH INTENSITY GRAZING SYSTEMS?
Research Effort
Conduct a farm-gate N
budget – pollution potential?
2 locations (farms)
2 10/10/10 Total fertilizer N applied and N losses associated with the
sampling period at Wrens (1 Jun 2008-31 Aug 2009) and
Quitman (1 Aug 2008-31 Aug 2009). (Eason, unpublished)
Fertilizer
Applied
Farm
Ammonia
Volatilized
Nitrate
Leached
Nitrate concentrations (a) and water
flux (b) from the Orangeburg soil on
the Wrens farm.
(c) Shows VWC for three depths in
the soil profile.
----------kg N ha-1 ----------Wrens Farm
605*
196
1.7
Quitman Farm
320#
7
40.4
* Applied as dry urea # Applied as UAN via irriga9on (Eason, unpublished) Nitrate concentrations (a) and water
flux (b) from the Stilson soil on the
Quitman farm.
Nitrate concentrations (a) and water
flux (b) from the Tifton soil on the
Quitman farm.
(c) Shows VWC for three depths in the
soil profile.
(c) Shows VWC for three depths in
the soil profile.
(Eason, unpublished) (Eason, unpublished) Farm-gate N balance for Wrens and Quitman
farms. (Eason, unpublished)
Farm-gate Balance: Nitrogen Inputs and
Outputs in Pasture-Based Dairies
Farm Records Farm Records Farm Records Farm Records Source
N input
*
% of Total N input
60394
33806
78.9
40.7
Grain Feed
11959
43679
15.6
52.6
Maize Silage
1224
0
1.6
0
Hay
3011
5587
3.9
6.7
Total
76589
83074
100
100
Milk
12066
14217
15.8
15.3
N/A
N output
N2O emmision
2032
? (~4000)
2.7
NH3 volatilization
23103
746
30.2
.90
NO3 Leached
204
4363
.3
17.1
Total
37407
19327
48
33.3
N in forage/soil
39182
60746
51
66.7
67%
89%
Experimental *
--------- kg N yr-1 ---------
Mineral Fertilizer
Experimental * Experimental N use efficiency
3 10/10/10 Accumulation of soil organic carbon in 3 paddocks
located in a pasture-based dairy in Wrens, GA. (2007-2009)
Initial
1 year
2 years
P4
0.625
0.670
0.725
1.277
P8
0.585
0.680
0.925
1.268
P14
0.663
0.950
1.083
1.163
Mean
0.624
0.767
0.911
1.236
------ % Soil Organic Carbon ------
For each 0.1% increase in organic carbon = 2000 lbs sequestered C.
3 years after grazing system started, averaging 3200 lbs sequestered C
per year
Greater soil water-­‐holding capacity Greater water infiltra9on rate in soil Greater soil nutrient reten9on capacity Nutrient “banking” % Soil organic C 1.25 1 0.75 0.5 2006 -­‐-­‐-­‐-­‐-­‐-­‐-­‐ Dry years -­‐-­‐-­‐-­‐-­‐-­‐-­‐ 2007 2008 Wet year 2009 2010 2011 Year soil was sampled Spatial complexity of soil organic matter forms at
nanometre scales. Lehman et al., 2008. Nature
Geoscience 1:238-242.
Implica9ons of Fixed Carbon: 1.5 1.5 3 years
% Soil organic C Paddock
Accumula9on of Organic Carbon in 3 Paddocks as a Func9on of Time ANer Conversion into Dairy Pasture, (Wrens, GA) Al and Desiree Wehner: “We are Aromatic a.a. (yellow)
Aliphatic (orange)
Carboxyl (red)
Phenolic (blue)
Soil particles are purple
not geZng the same fer9lizer response on our farm we started in 1993 as the ones we started in the last 3 years”. 1.25 1 “How long can we ‘mine’ the nutrients in the soil during periods of low milk prices?” 0.75 0.5 2006 2007 2008 2009 2010 2011 Year soil was sampled Lots of Challenges and Life Can Get Serious….
…. So Enjoy the Intangibles!!!
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