1. Evidence of Regime Shifts in Agroecosystems
Alex O. Awiti1 and Markus G. Walsh2
1The
Aga Khan University, Faculty of Arts and Science (East Africa)
2The Earth Institute at Columbia University, New York
Water for Food Global Conference
May 5-8, 2013
Lincoln, Nebraska, USA

2. Why Regime Shifts in Agroecosystems?
Regime Shift: Large and lasting changes in
structure/function
 Emphasis on sustainable food production systems and
recognition of the scarcity of vital resources such as
water, soil and biodiversity.
 Understanding the functioning of agro-ecosystems and
how their health and performance can be measured and
monitored over time and managed.

3. Random Cluster
Research Design
Control-Impact pair design
30 m
30 m

4. Field Sampling

Stratification Forest, Recent
Conversation, Historical
Conversion
30m by 30m plots (900m2);
Land use: land use history, land
use/land cover, time since
conversion, tenure
Soil properties: topsoil and
subsoil; standard soil
chemical, physical
assessments, stable carbon
isotopes
Soil hydraulic properties :
infiltration; water retention

5. Spectral Regimes
0.6
Recently Converted
Forest
Historically Converted
Relative reflectance
0.5
0.4
0.3
0.2
0.1
0
0
0.5
1
1.5
2
2.5
3
Wavelength (μm)
Wilks’ Lambda used to test the null
hypothesis that class means are identical
Value = 0.015, F= 12.63, p <0.0001
Out of 544 samples 94% were correctly classified.

6. Soil chemical properties and particle
size distribution Regimes
Soil chemical properties and particle size distribution measured in
Chronosequence age classes

7. Exploratory graphical assessment of the dynamics of
total SOC, C3- and C4-derived carbon with time since
conversion of forest soils to cropland. Zero (0) on the
X-axis denotes forest.
Awiti et al., 2008- Agric Ecosys Env
SOC Regimes
A model of decay patterns of total SOC, C3derived SOC and accretion C4-derived SOC.

8. Infiltration and Water retention
Regimes
0.700
3
0.600
S
Forest
2.5
Forest
RC
HC
Moisture content(vV-1)
Infiltration (cm/min)
3.5
2
1.5
1
A
0.5
RC
HC
0.500
0.400
Inflection
points
0.300
0.200
0
0
50
100
150
0.100
Time(min)
1
10
100
1000
Suction pressure (pa)
10000
100000

9. Primary
productivity
Regimes
0.0800
ln(Root:Shoot)
0.0400
0.0000
RC
-0.0400
-0.0800
-0.1200
HC
Forest

10. Terrestrial and Aquatic Regime
Shifts
80000
Tilapine
70000
Haplochromine
Catch (tons)
60000
R.argentea
50000
L.nilotica
40000
30000
20000
10000
0
1968
1973
1978
Year
1983
1988

11. An approach to building Agroecosystem Resilience
 Integrating trees and
woody perennials with
agricultural crops,
pastures and/or
livestock on the same
land management unit
to maintain structure
and function

12. Increase of 1 ton of soil carbon
pool in degraded cropland soils
increases maize yield by 10 -20
kg ha-1 .Carbon sequestration can
potentially offset fossil fuel
emissions by 0.4 to 1.2 gigatons
of carbon per year (Lal, 2004)

13. SOC pool under
natural forest
Planted Fallows
Relative SOC Pool
80
60
40
20
Plantation with
shade crop
Historic loss of SOC equals
sink potential
100
Rapidly growing
plantations
Conversion of
TFE to cropland
AF with
cover crops
No till with residue
mulch
Traditional cropping
Improved land use mgt
0
20
Time (yrs)
40

14. Advancing Agro-ecosystem
Resilience
 Diagnostic Indicators of Soil Condition (DISC)
– characteristic soil spectral profiles relative to benchmark sites biomass
allocation patterns
– hydraulic properties-water retention curves could revolutionize how we
evaluate and communicate soil quality to policy makers, farmers and
extension workers
 Strategic library of spectral baselines at watershed scale and/or AEZ for
development of Benchmark Similarity Index (BSI).
– Starting conditions and pathways and extent of degradation
 Establish optimal or allowable ranges for soil health and site index for crop
performance
– essential ingredients for monitoring and Anticipatory Management of soil
quality or timely intervention.