Evidence of Regime Shifts in Agro-ecosystems

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

Why Regime Shifts in Agro-ecosystems?

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.

30 m

30 m

Control-Impact pair design

Random Cluster Research Design

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

Field Sampling

Out of 544 samples 94% were correctly classified.

Wilks’ Lambda used to test the null hypothesis that class means are identicalValue = 0.015, F= 12.63, p <0.0001

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Wavelength (μm)

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ance

Recently Converted Forest Historically Converted

Spectral Regimes

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

Soil chemical properties and particle size distribution Regimes

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.

A model of decay patterns of total SOC, C3-derived SOC and accretion C4-derived SOC.

Awiti et al., 2008- Agric Ecosys Env

SOC Regimes

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Forest RC HC

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Suction pressure (pa)

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Forest RC HC

Inflection points

Infiltration and Water retention Regimes

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RC HC Forest

ln(R

oot:S

hoot

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Primary productivity

Regimes

1968 1973 1978 1983 19880

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Tilapine

Haplochromine

R.argentea

L.nilotica

Year

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ton

s)

Terrestrial and Aquatic Regime Shifts

Integrating trees and woody perennials with agricultural crops, pastures and/or livestock on the same land management unit to maintain structure and function

An approach to building Agro-ecosystem Resilience

Maize grain yield (t ha-1) from 2-year coppicing mixed fallow species treatments at Msekera, Eastern Zambia (Adapted from Mafongoya et al., 2006)

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)

SOC increase in tropical soils following IF with different tree species in the sub-humid tropics (Adapted from Albrecht & Kandji, 2003)

Rapidly growing plantations

Planted Fallows

Plantation with shade crop

AF with cover crops

No till with residuemulch

Traditional cropping

Improved land use mgt

Conversion of TFE to cropland

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SOC pool under natural forest

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Dynamics of soil organic carbon in TFEs. The rate of increase in the SOC pool depends on the restorative land use (from Lal, 2005)

Carbon Storage in Agroforestry systems (from Albrecht & Kandji, 2003)

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.

Advancing Agro-ecosystem Resilience