J. Viola Glenn1, Dr. Oluyede Ajayi2, Dr. Fred Cubbage1, Natasha James1, Darlene Casstevens3
1 NC State University, Department of Forestry and Environmental Resources 2 World Agroforestry (ICRAF) 3 NC State University, Department of Economics
31% of GDP in agriculture sector
15.9 million in population
2.8% increase in 2010, 17th fastest growing country in the world
Malawi
Importance of Study
Fertilizer tree indigenous to Africa and Middle East which is intercropped with agricultural crops
Increases food crop yields by 280% in experimental setting
Additional benefits: fuelwood, fodder for livestock, shade, timber
Faidherbia albida
Methods and Data
Can maize yield increases observed in experimental settings be observed in actual farming operations, managed independently of researcher guidance?
Population Growth and Food Security
Unsustainable dependence on expensive chemical fertilizer and reductions in food crop
yield
Depletion of soil nutrients and reduction
in overall soil fertility and quality
Shorter rest, or fallow, periods
between the planting of food crops
Pressure on arable land
Rapid population growth
Research Question
Data Collection, 2011
Semi-formal household survey of 391
subsistence smallholder farmers 509 individual fields, 72% with F. albida Two districts in the Central Region (Ntcheu
and Salima) Random sample generated from
comprehensive lists provided by Agriculture Extension
Data collected on : planting and maintenance costs of maize and F. albida, soil, trees, use of other technologies, demographics, non-yield tree benefits and general adoption attitudes
Data collected immediately after maize harvest by local university students to foster accurate recall and minimize communication issues
Mean/ % Yes
Min Max
Yield per acre (kg) (y) 611 10 2,160 Tree Characteristics (x1 – x3) Presence of trees (=1 if there is at least 1 tree in field)
71%
Trees per acre 4 0 32 Average diameter of trees (inches)
10 0 52
Farm and Field Characteristics (x4 – x8) District Ntcheu = 0 (50%)
Salima = 1 (50%) Use of hybrid maize 54% Soil fertility Poor (21%) = 0
Average (48%) = 1 Good (31%) = 2
Mkanda soil (=1 if soil is dark clay)
66%
Use of chemical fertilizer (=1 if used)
87%
Farmer Characteristics (x9 – x13) Dwelling type (income proxy)
Mud brick (35%) = 0 Poles/straw (0%) = 0 Burned brick (65%) = 1
Age of head of household 46 18 93 Agroforestry experience (years)
11 0 51
Education level of head of household
None (13%) = 0 Primary School (not completed) (58%) = 1 Primary School (completed) (16%) = 2 Secondary school (11%) = 3 Post-secondary school (1%) = 4
Household type Husband and wife (77%) = 0 Single male (1%) = 0 Single female (22%) = 1
Summary of Key Variables
Results
Regression Coefficients
Model: y = f(xi) 3 Ordinary Least Squares models with
different independent variables (xi) to represent trees
Dependent variable (y) - maize yield / ac (kg) N = 491
1 2 3 Tree Characteristics Presence of trees 86.0*** Trees per acre 22.5*** Trees per acre, squared -0.6** Average diameter of trees (inches)
6.3***
Farm and Field Characteristics District (=1 if in Salima district)
71.7*** 82.2*** 92.9***
*Hybrid maize (=1 if field uses hybrid maize)
47.1* 45.9* 49.3*
Soil fertility 51.2*** 47.5** 60.8*** Mkanda soil (=1 if soil is dark/clayey)
61.0** 59.3** 48.5*
Farmer Characteristics Dwelling/income proxy (=1 if housing type is burned brick)
85.4*** 84.2*** 80.7***
Age (head of household) -2.6*** -2.4*** -2.9***
Adjusted R2 0.10 0.12 0.12
*** significant at 1% • ** significant at 5% • * significant at 10%
Conclusions
Each metric shows a significant positive relationship between yield and F. albida
Yield increase is 10% to 14%, at the mean (~78kg per acre), equivalent to Malawi government estimates of the amount of maize required to feed an adult for 3 to 4 months
(1) Trees are correlated with greater maize yields
(2) Environmental fixed effects and income are also important
Environmental fixed effects are captured in the District variable which includes all fixed variations between the two regions: altitude, climate, precipitation, soil moisture content, etc.
Type of dwelling is used as a proxy for income, with burned brick homes used as an indicator of relative wealth
Both variables have impacts similar to that of F. albida in magnitude and significance
Additional data are available on gender of respondent, number of household members
Further testing of methods for representing presence of trees may yield better fitting models, e.g. one which uses both diameter and density
Detailed financial assessment of cost of planting and maintaining F. albida
Caveats
Maize yield and field size data rely on farmer recall rather than direct measurement, though resulting distribution of yield per acre is relatively normal
Soil fertility status is also self-assessed using a quantitative scale, which limits the study’s ability to make causal connections between fertility and the presence of trees
Future Work
Acknowledgements
ICRAF (Dr. Oluyede Ajayi, Dr. Frank Place, Dr. Dennis Garrity, Dr. Tracy Beedy, Innocent Phiri, Maurice Zimba); NCSU (Dr. Fred Cubbage, the Laarman Grant, Natasha James, Darlene Casstevens, Dr. Melinda Morrill); USAID
o Reverse leaf phenology from crops o Nitrogen fixing o Roots improve soil structure