Greenhouse Gas Emissions and Fertiliser
Quality from Cattle Manure Heaps in Kenya
Session “Climate change - Mitigation and adaptation”, Tropentag Virtual Conference 2020
Sonja Leitner, George Wanyama, Dónal Ring,
Daniel Korir, David Pelster, John Goopy,
Klaus Butterbach-Bahl, Lutz Merbold
s.leitner@cigar.org
International Livestock Research Institute (ILRI),
Nairobi, Kenya
10 Sept 2020
Better lives through livestock

Background
Manure applied to soils
Enteric fermentation
Manure left on pasture
Manure management
Burning - savanna
Synthetic fertilizer
Rice cultivation
Crop residues
Cultivation org. soils
Burning – crop res.
AFOLU GHG emissions
by source (globally)
FAO, Tubiello et al. 2014
• 25% of global AFOLU GHG
emissions from livestock manure
• African countries rely on default IPCC
emission factors for GHG reporting
• Few in situ data on manure GHG
emissions from smallholder systems
• Low livestock productivity in SSA:
 Low forage quality: tropical grasses with
low protein and high fibre content
 Low fertilizer use: soil nutrient mining
 Need for sustainable intensification and
closed nutrient cycles

Research questions & hypotheses
Q1: What is the magnitude of CH4 and N2O emissions from manure heaps in Kenyan
smallholder farming systems?
Q2: How do animal diets affect manure CH4 and N2O emissions and manure fertilizer
quality?
H1: Manure from hungry cows has lower N concentrations and emits less N2O
compared to well-fed cows because of higher N retention under sub-maintenance
energy feeding.
H2: Poor quality tropical forage grasses result in manure with low N concentrations
and low manure N2O emissions.
H3: Forage grass with a low DM content will increase manure moisture content and
lead to higher manure CH4 emissions.

Animal trial 1: Sub-maintenance feeding
• Setup: Animal feeding trial with local Boran
cattle (1.5 yr young steers) fed below their
metabolic energy requirements (MER)
 100 % MER (ok)
 80 % MER (hungry)
 40 % MER (really hungry!)
• 100 kg FW manure incubated in heaps (n = 3)
 CH4 and N2O fluxes measured with manual static
chambers for 5 months (daily to 3x/week gas sampling)
 Manure chemistry (DM, C, N, ash)
© George Wanyama
& Daniel Korir
Mazingira Centre,
ILRI Campus,
Nairobi, Kenya
mazingira.ilri.org

Animal trial 1: Sub-maintenance feeding
*
*
*
IPCC default
0.0
1.0
2.0
3.0
4.0
5.0
120%
MER
100%
MER
60%
MER
gCH4-Ckg-1DM
Cumulative CH4 flux
b
a
a
0
20
40
60
80
100
120
140
160
120%
MER
100%
MER
60%
MER
mgN2O-Nkg-1DM
Cumulative N2O flux
0.0%
0.2%
0.4%
0.6%
0.8%
1.0%
120%
MER
100%
MER
60%
MER
%manure-CemittedasCH4-C
EF CH4
*
*
*
IPCC default
0.0%
0.2%
0.4%
0.6%
0.8%
1.0%
1.2%
120%
MER
100%
MER
60%
MER
%manure-NemittedasN2O-N
EF N2O
IPCC default
(manure solid storage)
• Manure N2O emissions of hungry cattle
lower than when fed at maintenance
levels
• No difference in manure CH4 emissions
between diets
• CH4 emissions and N2O emission
factors lower than IPCC Tier 1
default values for solid storage
100%
MER
80%
MER
40%
MER
100%
MER
80%
MER
40%
MER
100%
MER
80%
MER
40%
MER
100%
MER
80%
MER
40%
MER

Animal trial 1: Sub-maintenance feeding
• Manure from hungry cattle contains less N and has higher C:N
 lower fertilizer value!
30
32
34
36
38
40
42
44
120%
MER
100%
MER
60%
MER
ManureCconcentration(%)
initial
final
*
b
ab
a
c
b
a
0.0
0.5
1.0
1.5
2.0
2.5
120%
MER
100%
MER
60%
MER
ManureNconcentration%
a
ab
b
a
ab
b
0
5
10
15
20
25
30
35
40
45
120%
MER
100%
MER
60%
MER
ManureC:N
initial
final
Manure C:N ratio
100%
MER
80%
MER
40%
MER
100%
MER
80%
MER
40%
MER
100%
MER
80%
MER
40%
MER
Manure N concentrationManure C concentration
European dairy cow
Amon et al., 2001

Animal trial 2: Tropical forage grass diets
• Setup: Animal feeding trial with local Boran
cattle (1.5 yr young steers) fed only with
tropical forage grasses
 Napier grass (Pennisetum purpureum var Kakamega 1)
 Rhodes grass (Chloris gayana cv. Boma)
 Brachiaria grass (Brachiaria brizantha var xaeres)
• 100 kg FW manure incubated in heaps (n = 3)
 CH4 and N2O fluxes measured with manual static
chambers for 5 months (daily to 3x/week gas sampling)
 Manure chemistry (DM, C, N, ash)
© Jake Meyers &
Dónal Ring
Mazingira Centre,
ILRI Campus,
Nairobi, Kenya
mazingira.ilri.org

Animal trial 2: Tropical forage grass diets
IPCC default
(manure solid storage)
• No difference in manure N2O emissions
between grass diets
• Manure CH4 emissions of cattle fed on
Rhodes grass lower than fed on Napier
or Brachiaria
• CH4 emissions and N2O emission
factors lower than IPCC Tier 1
default values for solid storage

Animal trial 2: Tropical forage grass diets
• No difference in manure chemistry or moisture
• C:N ratio 3x higher compared to “European diet”  poor fertilizer value
European dairy cow
Amon et al., 2001

Conclusions
• Manure GHG emissions depend on cattle diet: feet scarcity and poor-
quality forage grasses reduce N2O emissions
• Smallholder farming systems in East Africa quite unique & diverse
 Tier 1 assumptions and default values often not valid
 over-estimation of manure GHG emissions with default values
 need for localized measurements
• Future experiments must consider breeds (local vs. improved), feed
quality & quantity, manure storage type & duration, climate

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