Drought resilience of maize-legume agroforestry systems in Malawi

212 Pages·2012·27.23 MB·English

by  Amber Kerr

UC Berkeley
UC Berkeley Electronic Theses and Dissertations
Title
Drought resilience of maize-legume agroforestry systems in Malawi
Permalink
https://escholarship.org/uc/item/7bm3k6nv
Author
Kerr, Amber Catherine
Publication Date
2012

Peer reviewed|Thesis/dissertation
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Drought resilience of maize-legume agroforestry systems in Malawi

By

Amber Catherine Kerr

A dissertation submitted in partial satisfaction of the
requirements for the degree of
Doctor of Philosophy
in
Energy and Resources
in the
Graduate Division
of the
University of California, Berkeley

Committee in charge:
Professor Margaret S. Torn, Chair
Professor John Harte
Professor Lynn Huntsinger

Fall 2012

Abstract

Drought resilience of maize-legume agroforestry systems in Malawi

by

Amber Catherine Kerr

Doctor of Philosophy in Energy and Resources

University of California, Berkeley

Professor Margaret Torn, Chair

Agroforestry – the practice of growing trees and crops on the same land – has recently been
suggested as a potential tool for adaptation to climate change. There are many mechanisms by
which trees on farmland could help to ameliorate climatic stresses: moderation of microclimate,
increased soil water-holding capacity, increased infiltration, reduced runoff, complementary use
of water resources, and diversification of production risk. However, these benefits remain largely
speculative, with very few controlled experiments to demonstrate them. Furthermore, little is
known about how agroforestry systems themselves might be adversely affected by climatic
stress, especially during the vulnerable stage of seedling establishment.

This dissertation attempts to address some of these questions with regard to “fertilizer tree”
agroforestry systems in Malawi. In these systems, maize is intercropped with fast-growing
leguminous trees, and biomass from the trees is regularly incorporated into the soil to increase
crop yields. Though fertilizer trees are demonstrably effective under normal climatic conditions
in southern Africa, their drought tolerance has not been systematically examined. For this three-
year project (2008-2011), a novel and low-cost rain exclusion shelter design was used to impose
an artificial drought on several Gliricidia sepium and Tephrosia candida fertilizer tree systems at
Makoka Agricultural Research Station (15º31’S, 35º13’E) in southern Malawi.

In the first experiment, a mature Gliricidia-maize intercropping system was subjected to
complete rain exclusion from maize anthesis to maize harvest during the 2009-2010 and 2010-
2011 growing seasons. Monoculture maize was used as a control. The drought dramatically
decreased maize yields in both years (by 61% and 39%, respectively), with approximately
similar decreases in both Gliricidia and monoculture plots. This implies that Gliricidia does not
protect maize from drought conditions, but neither does it exacerbate the effects of drought by
competing with maize for water. Whether in the presence or absence of drought, maize yields in
Gliricidia plots were higher than in monoculture plots. Gliricidia had no effect on soil moisture
and had a slight cooling effect on microclimate at the end of the growing season.

In the second experiment, a similar drought – compounded with the additional stress of late
planting – was imposed upon newly established fertilizer tree systems of three types: Gliricidia-
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maize intercropping, Tephrosia-maize relay intercropping, and Tephrosia improved fallows.
Seedling survival, growth, and biomass production were monitored for signs of adverse effects.
Results varied by species: Gliricidia growth was retarded by drought and late planting, but
Gliricidia survival remained near 100%, and its biomass at the end of the growing season was
not affected. By contrast, Tephrosia maintained constant height growth under these stresses, but
its survival decreased, which translated into lower maize yields the following year. However, all
three fertilizer tree systems demonstrated good overall drought resilience and conferred maize
yield benefits even under suboptimal conditions.

A modeling experiment was conducted to compliment the above field experiments. Output from
global and regional climate models was applied to long-term data sets on weather and maize
yield at this location. The results suggested that for the next several decades, current precipitation
variability in southern Malawi will likely pose a greater risk to maize production than will long-
term precipitation trends caused by global climate change. However, higher maximum
temperatures have the potential to reduce maize yields within the next several decades.

The field experiments described herein suggest that fertilizer tree systems can improve maize
production even under conditions of drought stress. Current climate variability and future climate
change should pose no obstacle to their adoption in Malawi. Although this project did not find
evidence that fertilizer trees directly protect the maize crop from drought, their beneficial effects
on food security and farm income may indirectly help to cushion farmers against climate
variability.

The performance of agroforestry systems under future climate is a topic that demands much
more research, both descriptive and theoretical (including controlled experiments, simulation
models, and meta-analyses). Furthermore, climate manipulation experiments in the developing
world are an underutilized but potentially important tool for understanding the effect of climate
change on subsistence agricultural systems and developing climate-resilient alternatives. It is
hoped that the methods and outcomes of this dissertation represent a small step toward closing
both of those knowledge gaps.
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Dedication

To my grandmother,
Catherine “Kay” Kerr (1911-2010).
Principled, stubborn, courageous, and tireless,
she worked to preserve the health and beauty
of the San Francisco Bay for future generations.
Many are grateful for her inspiring legacy,
but none more so than her granddaughter.

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Table of contents

Chapter 1. Role of agroforestry in climate adaptation .............................................................. 1

Abstract ....................................................................................................................................... 1

1.1
  Reducing vulnerability of agriculture to climate change ................................................... 1

1.1.1
  Current approaches to agricultural adaptation ............................................................ 2

1.1.2
  Agroecological perspectives on climate resilience ..................................................... 2

1.1.2.1
  Insights from traditional knowledge .................................................................... 2

1.1.2.2
  Ecosystem mimicry .............................................................................................. 3

1.2
  Definitions and examples of agroforestry .......................................................................... 3

1.2.1
  Definition and scope ................................................................................................... 3

1.2.2
  Theoretical bases of agroforestry ................................................................................ 3

1.2.3
  Common elements of agroforestry systems ................................................................ 5

1.2.4
  How might agroforestry play a role in climate adaptation? ........................................ 5

1.3
  Climate modulation by agroforestry systems: direct effects .............................................. 5

1.3.1
  Microclimate ............................................................................................................... 6

1.3.1.1
  Air and soil temperature ....................................................................................... 6

1.3.1.2
  Evaporative demand ............................................................................................. 6

1.3.2
  Soil properties ............................................................................................................. 6

1.3.2.1
  Soil water-holding capacity ................................................................................. 6

1.3.2.2
  Changes in infiltration and runoff ........................................................................ 6

1.3.2.3
  Water use competition or complementarity ......................................................... 7

1.3.2.4
  Hydraulic lift ........................................................................................................ 7

1.3.2.5
  Soil nutrient status................................................................................................ 7

1.3.3
  Physical protection against storm damage .................................................................. 8

1.4
  Climate modulation by agroforestry systems: indirect effects .......................................... 8

1.4.1
  Biodiversity conservation ........................................................................................... 8

1.4.2
  Weeds, pests and diseases ........................................................................................... 9

1.4.3
  Risk management by diversification of production .................................................... 9

1.4.4
  Enhancing farm productivity and income ................................................................... 9

1.5
  Impacts of climate change on agroforestry systems ........................................................ 10

1.5.1
  Precipitation .............................................................................................................. 10

1.5.2
  Temperature .............................................................................................................. 10

1.5.3
  CO fertilization ........................................................................................................ 11

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1.5.4
  Extreme events and natural disasters ........................................................................ 11

1.6
  Synergies and conflicts between adaptation and mitigation ............................................ 12

1.6.1
  Previous work on climate mitigation aspects of agroforestry ................................... 12

1.6.2
  Potential synergies .................................................................................................... 12

1.6.3
  Potential conflicts ...................................................................................................... 13

1.7
  Need for future work ........................................................................................................ 14

1.7.1
  Experimental climate manipulations in the field ...................................................... 14

1.7.2
  Simulation modeling ................................................................................................. 14

1.7.3
  Meta-analyses of agroforestry climate response across space and time ................... 15

1.8
  Conclusions ...................................................................................................................... 15

1.8.1
  Acknowledgements ................................................................................................... 15

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Chapter 2. Introduction to Malawi field experiments ............................................................. 17

Abstract ..................................................................................................................................... 17

2.1
  Motivations and goals of this project ............................................................................... 17

2.1.1
  Protecting food security in the developing world under future climate .................... 18

2.1.1.1
  Identifying climate-resilient production systems in vulnerable areas ................ 18

2.1.1.2
  Meeting the need for more climate manipulation experiments ......................... 18

2.1.2
  Understanding response of agroforestry systems to climate change ........................ 18

2.1.2.1
  Gathering empirical evidence on climate response of agroforestry systems ..... 19

2.1.2.2
  Elucidating mechanisms and interactions .......................................................... 19

2.2
  Background on Malawian agriculture .............................................................................. 19

2.2.1
  Current statistics ........................................................................................................ 20

2.2.1.1
  Demographic and economic statistics ................................................................ 20

2.2.1.2
  Agricultural statistics ......................................................................................... 21

2.2.2
  History of agriculture in Malawi ............................................................................... 22

2.2.2.1
  Pre-colonial introduction of maize ..................................................................... 22

2.2.2.2
  The agricultural estate system ............................................................................ 22

2.2.3
  Challenges to agricultural production in Malawi ...................................................... 23

2.2.3.1
  Poor soil fertility and lack of access to inputs ................................................... 23

2.2.3.2
  High rainfall variability ...................................................................................... 24

2.2.3.3
  Population density and small farm size ............................................................. 24

2.2.3.4
  Economic and social challenges ........................................................................ 24

2.2.4
  Fertilizer subsidy: history, successes, costs .............................................................. 25

2.2.4.1
  Starter Pack Scheme and Targeted Input Programme, 1998-99 to 2004-05 ...... 25

2.2.4.2
  Farm Input Subsidy Programme (2005-06 to present) ...................................... 25

2.3
  Agroforestry research in southern Africa ........................................................................ 26

2.3.1
  History and goals of SADC-ICRAF ......................................................................... 26

2.3.2
  Experiments on fertilizer trees .................................................................................. 26

2.3.2.1
  Tree species used ............................................................................................... 26

2.3.2.2
  Types of fertilizer tree systems .......................................................................... 27

2.3.3
  Adoption and livelihood impacts of fertilizer trees .................................................. 29

2.4
  Gaps filled by the current project ..................................................................................... 30

2.4.1
  Examining crop and tree response to controlled drought ......................................... 30

2.4.2
  Comparing mature trees and seedlings ..................................................................... 30

2.5
  Outline of experimental methods ..................................................................................... 30

2.5.1
  Makoka Agricultural Research Station ..................................................................... 30

2.5.2
  Philosophy of three-year field experiment ................................................................ 31

2.5.3
  Allocation of field tasks ............................................................................................ 31

2.5.4
  Allocation of field tasks ............................................................................................ 32

2.5.5
  Scope, implications, and limitations of this work ..................................................... 33

2.5.6
  Acknowledgements ................................................................................................... 34

Chapter 3. Design, construction, and performance of rain exclusion shelters ...................... 35

Abstract ..................................................................................................................................... 35

3.1
  Introduction and motivation ............................................................................................. 35

3.1.1
  Intrinsic challenges of manipulating precipitation .................................................... 36

3.1.1.1
  Intercepting target amount, versus achieving a realistic temporal pattern ......... 36

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3.1.1.2
  Difficulty in controlling all aspects of plant-water relations ............................. 37

3.1.1.3
  Unintended consequences .................................................................................. 37

3.1.2
  Existing rainout shelter designs ................................................................................ 37

3.1.2.1
  Shelters with fixed or removable roofs .............................................................. 37

3.1.2.2
  Fractional interception with slats or gutters ....................................................... 38

3.1.2.3
  Below-canopy interception of throughfall ......................................................... 38

3.1.2.4
  Watering experiments ........................................................................................ 38

3.1.3
  Goals of this project .................................................................................................. 38

3.2
  Methods............................................................................................................................ 39

3.2.1
  Design of rain shelters .............................................................................................. 39

3.2.2
  Evaluating rain shelter performance ......................................................................... 44

3.2.2.1
  Rainfall interception ........................................................................................... 44

3.2.2.2
  Soil moisture ...................................................................................................... 44

3.2.2.3
  Leaf water content .............................................................................................. 45

3.2.2.4
  Litter decomposition rates .................................................................................. 45

3.2.2.5
  Light interception ............................................................................................... 45

3.2.2.6
  Pan evaporation .................................................................................................. 46

3.2.2.7
  Soil temperature ................................................................................................. 46

3.2.2.8
  Air temperature .................................................................................................. 46

3.3
  Performance of rain shelters ............................................................................................ 46

3.3.1
  Intended effects ......................................................................................................... 46

3.3.1.1
  Total rainfall ....................................................................................................... 46

3.3.1.2
  Litter decomposition .......................................................................................... 47

3.3.1.3
  Gliricidia leaf water content ............................................................................... 47

3.3.2
  Unintended effects .................................................................................................... 48

3.3.2.1
  Air temperature .................................................................................................. 48

3.3.2.2
  Pan evaporation .................................................................................................. 48

3.3.2.3
  Soil temperature ................................................................................................. 48

3.3.2.4
  Incident radiation: significant effect .................................................................. 49

3.3.2.5
  Dust on leaves .................................................................................................... 49

3.3.3
  Durability .................................................................................................................. 50

3.3.3.1
  Roof durability under normal conditions ........................................................... 50

3.3.3.2
  Violent storms: weathered successfully ............................................................. 50

3.3.3.3
  Termites: a major problem ................................................................................. 50

3.4
  Discussion ........................................................................................................................ 51

3.4.1
  Possible improvements to existing design ................................................................ 51

3.4.1.1
  Incident radiation ............................................................................................... 51

3.4.1.2
  Surface and belowground water flow ................................................................ 51

3.4.1.3
  Attack by termites .............................................................................................. 52

3.4.1.4
  Insufficient roof height for trees ........................................................................ 52

3.4.1.5
  Control for confounding effects by watering under shelters ............................. 52

3.4.2
  Future applications .................................................................................................... 53

3.4.2.1
  Other crops and other locations ......................................................................... 53

3.4.2.2
  Introduce heating or other variables .................................................................. 53

3.5
  Conclusions ...................................................................................................................... 53

3.5.1
  Acknowledgements ................................................................................................... 54

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