KIT – The Research University in the Helmholtz Association
INSTITUTE OF METEOROLOGY AND CLIMATE RESEARCH, ATMOSPHERIC ENVIRONMENTAL RESEARCH, IMK-IFU
DIVISION OF BIO-GEO-CHEMICAL PROCESSES
www.imk-ifu.kit.edu
The effects of climate on decomposition of cattle, sheep and goat manure in
Kenyan tropical pastures
PhD student: Yuhao Zhu
Supervisor: Klaus Butterbach-Bahl

Institute of Meteorology and Climate Research, IMK-IFU,
Division and/or Working Group
2 23.09.2020
Decomposition:
The physical & chemical breakdown of dead organic matter
C cycling:
More than half of net primary production (NPP) is returned to the soil (David et al.
2004)
It also results in CO2 emissions to the atmosphere of about 60 Pg C yr-1 (Houghton
2007)
N cycling:
Internal recycling of nitrogen (N) from litter decomposition is also the primary
source of N for most ecosystems (Parton et al. 2007; Chapin et al. 2012)
Introduction

Institute of Meteorology and Climate Research, IMK-IFU,
Division and/or Working Group
3 23.09.2020
Biomass
Litter
input
Manure
input
Grazing animals
Manure is important for C&N cycle in grazing system
Grazing animals consume large amounts of biomass that often reduce litter
inputs to soil (Güsewell et al. 2005; Tanentzap and Coomes 2012)
Grazing system

Institute of Meteorology and Climate Research, IMK-IFU,
Division and/or Working Group
4 23.09.2020
Smallholder mixed-crop and pastoral livestock systems
➢ Average farm size 0.5-2 h
➢ Pasture-fed
➢ Daily grazing
➢ No fertilization
Manure decomposition?
Photos from Wanyama Ibra
Manure still exist for months to years.

Institute of Meteorology and Climate Research, IMK-IFU,
Division and/or Working Group
5 23.09.2020
Litter decomposition pattern
Exponential decay: 𝒌 = 𝐥𝐧(𝑴 𝒕/𝑴 𝟎) (−𝟏/𝐭)
Decomposition
Litter quality
decomposer
community
climate

Institute of Meteorology and Climate Research, IMK-IFU,
Division and/or Working Group
6 23.09.2020
Objectives
1) measure changes in manure dry matter, C and N concentrations over
time after manure deposition;
2) determine if manure type (i.e. animal species) affects manure
decomposition rates; and
3) determine how climate affects manure decomposition.
Hypothesis:
1) manure decomposition would also follow exponential decay;
2) manure decomposition rates would be faster for manure with lower
initial C/N ratios and higher initial N concentrations; and
3) manure would decompose faster under wetter and warmer climatic
conditions.

Institute of Meteorology and Climate Research, IMK-IFU,
Division and/or Working Group
7 23.09.2020
CATTLE
SHEEP
GOAT
Taita
EMBU
Kapiti
ILRI,
Nairobi
18.0to22.9°C
209to1372mm
Manure bags: 69 bags for each manure type at each site
Sampling weekly, biweekly or monthly over 378 d
Experimental design

Institute of Meteorology and Climate Research, IMK-IFU,
Division and/or Working Group
8 23.09.2020
Temporal dynamic of dry matter loss
→ Dry matter decreased exponentially

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Division and/or Working Group
9 23.09.2020
→ N mineralization < C mineralization
→ decreasing C/N ratios
Temporal dynamic of changes in C/N ratios and N
concentrations

Institute of Meteorology and Climate Research, IMK-IFU,
Division and/or Working Group
10 23.09.2020
Dry matter decomposition rates
→ Both manure type and climate influenced manure decomposition rates

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Division and/or Working Group
11 23.09.2020
→ Cattle manure has highest cellulose and cellulose decomposes fastest
→ Decomposition rate increases with increasing cellulose/ N ratio
Changes in chemical characteristics during
decomposition

Institute of Meteorology and Climate Research, IMK-IFU,
Division and/or Working Group
12 23.09.2020
→ Rainfall amount limits manure decomposition under tropical climate.
Effects of climate factors

Institute of Meteorology and Climate Research, IMK-IFU,
Division and/or Working Group
13 23.09.2020
Thank for your attention
Photos by Lutz Merbold