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• How to identify and characterize key environmental factors affecting crop genetic diversity and productivity
• How to collect and analyse information on farmers’ knowledge of their biophysical environments
• The potential role of crop genetic diversity in supporting ecosystem functions.
Chapter 6: Abiotic and Biotic Environment
Abiotic and biotic factors vary
• Over time (with seasonal, annual, and stochastic changes) and
• In space, from micro-environmental to eco-regional scales
Geographical
• topography,
• altitude,
• slope,
• aspect
Climatic Factors
• Temperature: fluctuations and extremes
• Water: amount and distribution of rainfall
• Light: light intensity
• Wind: wind velocity
• Air: levels of CO2 concentration
Soils• texture, fertility, toxicity, moisture
North Carolina State University
Environmental Disturbance and Climate Change
Carbon Dioxide Levels and Climate Change
Biotic Components of Agricultural Ecosystems• Pathogens
• Pests
• Biological Control Agents
• Weeds
• Soil Organisms
• Pollinators
Functional group Influence
Earthworms --soil porosity and soil nutrient relations through channeling, and
ingestion of mineral and/or organic matter
Termites and ants --soil porosity and texture through tunneling, soil ingestion and transport,
and gallery construction
--nutrient cycles through transport, shredding, and digestion of organic
matter
Other macrofauna
such as woodlice,
millipedes, insect
larvae
--act as litter transformers, with an important shredding action on dead
plant tissue and their predators (centipedes, larger arachnids, some other
types of insect)
Nematodes --turn over soil in their roles as root grazers, fungivores, bacterivores,
omnivores, and predators
--occupy existing small pore spaces in which they are dependent on
water films
--usually have very high generic and species richness
Mycorrhizae --associate with plant roots, improving nutrient availability and reducing
attacks by plant pathogens.
--different varieties of a crop can respond differently to inovulation with
mycorrhizae (wheat) and colonization by mycorrhize is dependent on
host genotype (pearl millet)
Rhizobia --N-fixing microsymbionts, which transform N2 into forms available for
plant growth
Microbial biomass --an indirect measure of the total decomposition and nutrient recycling
community of a soil. Microbial biomass is contributed by three very
diverse taxa: fungi, protists, and bacteria (including archaea and
actinomycetes); however it is not usually practical to separate these
during measurements.
Sources: Swift and Bignell (2001); Moreira et al. (2008).
Key functional groups of soil organisms
Farmer characterization of their abiotic and biotic environment
Farmers’ ecological knowledge is systematic
• Farmers possess detailed folk taxonomies for identifying and classifying the abiotic and biotic components of the environment.
• Based on their experiences and perceptions, farmers characterize and develop classification systems or ethno-taxonomies for plants, animals, soils, weather phenomena, vegetation types, landforms, for stages of ecological succession, pests and diseases, weeds, plant competitors, mutualists, and other ecological domains
A suggested list of environmental domains and their dimensions to discuss with farmers.
Domain Dimensions to discuss with farmers
Landform Elevation, location and shape, includes hill tops, rivers, valley
bottoms, plateaux, cliffs
Soil Color, texture, fertility, acid-alkalinity, workability, humidity,
consistency, drainage profile, utility, salinity, living matter in the soil,
susceptibility to soil erosion, leaching
Climate Temperature, rainfall, evapotranspiration, elevation, exposure,
topography (including position of land masses and bodies of water)
wind, seasonality
Surrounding
vegetation
type
Floristic composition (including dominant species), extent of human
management/ disturbance, indicator species of the surrounding
vegetation, weeds
Land-use
zone
Technology applied, extent of management, distance to household,
ownership
Stage of
ecological
succession
Shifting cultivation importance, number of fallow years, extent of
original disturbance
Farmers' soil classification and maize diversity conservation in Yucatán, Mexico
Soil† Ts
ek
’el
Bo
x-l
u’u
m
Pu
s-l
u’u
m
Ek
-lu
’um
Ch
ac
-lu
’um
Ka
nk
ab
Ya
’ax
om
Ak
’alc
he
Litosol √ Rendzine √ √ √ √ Cambisol √ √ √ Luvisol √ √ √ √ Nitosol √ Vertisol √ √
Gleysol √
This detailed soil classification system is an important aspect of landrace
cultivation in Yaxcabá village, Yucatán, Mexico, where farmers plant different
maize varieties to land area with specific soil and topography types, based on
the varieties' time to maturity. Long-season maize is planted to higher, rockier
soil, while early maturing varieties are planted to level areas of red, organic
soils, such as in home gardens (Arias et al. 2000).
FAO
Defining healthy and non healthy plants
Healthy Not healthy Disease Pest
Healthy Not healthy
The descriptions of unhealthy plants
13 descriptors
• Green leaf
• Growing well
• Plump seed
• High yield
• Large spike
• More tillering
12 descriptors
• Spot on leaf
• Leaf wither
• Insect hole
• Dwarf plant
• Smaller grain
Farmer descriptions of healthy plants Barley, China; Guo et al. 2011)
Identification pest and diseases and their effect on the crop
Pest/disease description
Plant part affected
Stage affected
Descriptive
traitsStagePlant partPest/
Diseases
pestes/
enfermedades Description hojas tallos raices vaina
grano o
semilla
Flora-
cion vaina 2o desh
lancha X x
frutos manchados
(vainas) X x
plantas sin hojas X X X x
pudrición o lancha x x
planta sin hojas y
frutos manchados X X x
otras enfermedades
que Vd no conoce X x
Etapa del cultivoParte afectada Growth stagePlant part affected
Farmers’ descriptions of pests/diseases
Pest/disease
Descriptions
rust
smut
aphid
cutworm
yellow dwarf
(Shangri-la)
Weevil
(Songming)
the leaves withered, rust on the leaves and
stems, dwarf, small spikes, small grains, low
yields
the spikes became black, no grain
sucked the juice, yellow leaves and stems, slow
growth, shriveled grains
broken roots, plants died
dwarf, yellow leaves, low tillers, low yields
insect holes in the grains
Barley, Yunnan, China – Guo et al. 2011)
Parts and stages damaged by pest/disease
Pest/disease
Damage positions Damage stages
leaf stem spike root grain seeding tiller heading maturity grain
rust
smut
aphid
cutworm
yellow dwarf
weevil
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
pest/dis
ease
types of damageOverall
importance of
pest/disease
yiel
d
grain
size
fee
d
heig
ht
rust 3 4 3 3 3
smut 4 1 4 4 4
aphid 1 2.5 2 2 2
cutwor
m5 5 5 5 5
yellow
dwarf2 2.5 1 1 1
Farmers’ beliefs on origin of pests and diseases
23 reasons
• Drought
• Rain
• Soil
• Pest
• Tree, grass and ditch
• Neighboring fields
• Air
• Most farmers considered:
• Dry year –
• Wet year +
• Hot year –
• Cold year +
Majority of the farmers believed that the barley in a wet,
cold year had higher resistances than in a dry, hot year
Songming, Yunnan, China, (Guo et al., 2011)
Temperate Central Asia and Tropical SE Asia Fruit Tree Diversity:
A shared hypothesis:
“Variety diversity of fruit trees increases levels of pollination service and increases productivity”
Apple pollination Mango pollination
Environmental factor Possible farmer response to alter environment
Extreme cold Crop sheltering, frost coverage
Extreme heat Crop shading
High clay content/poor drainage Removal of hardpans, addition of drainage lines
High sand content/rapid drainage Addition of water retention lines
High gravel/rock content Removal or rock material
High or low pH Fertilizers, soil additives
Low nutrient content Fertilizers, soil additives, intercropping, crop
rotation with legumes
High aluminum or salt content Fertilizers, soil additives
High precipitation/waterlogged
soils
Addition of drainage lines
Low annual precipitation Irrigation systems/ water harvesting
Low seasonal precipitation Temporary/seasonal irrigation systems
Desertification Sand barriers
High erosion potential Flattening field slopes, developing terraces
Low light intensity Thinning possible shade
Long/short photoperiod Agroforestry, crop rotation
Strong local winds Plant/build windbreaks, agroforestry
Pests Pesticides, physical barriers, intercropping, crop
rotation
Diseases Avoidance of conditions favorable to disease,
fungicides, crop rotation
Plant competition Weeding, reduced plant spacing, herbicides
Environmental stresses and possible agronomic management responses by farmer
Crop genetic diversity
(intra-specific diversity)
continuous biomass
ensured
Different
resource
acquisition
efficiency
Increased facilitative
interactions
Increase in number of
functional traits
Production system more
resistant and resilient to
disturbance
Specific
resistance to
pests and
diseases
Diversity of
pollinators
supported
Reduced
movement of
pest and
disease
Genotype
complement
-arity
Increased N-
Fixation
Improved soil
processes
Improved soil
processes (soil
formation; N-
fixation; organic
matter)
CO2
sequestration
Longer
period of
food for
pollinators
Decompo
sition and
nutrient
cycling
Pest and
disease
control
More
efficient
pollination
longer period
for CO2
sequestration
Reduced
soil erosion
more efficient
CO2
sequestration
Improved ecosystem functions
Differing
architecture
reduces stress to
other genotypes
Pollinator
sharing
attraction
Longer
period of
vegetation
coverage
Improved ecosystem functions
More diversity in
specific resistance
to pests and
diseases
Increase in number
of functional traits
continuous
biomass ensured
Production system
more resistant and
resilient to
disturbance
Increased facilitative
interactions
Pest and disease regulation
Different
resource
acquisition
efficiency
Genotype
complement
-arity
Differing
architecture
reduces stress to
other genotypes
The mixture effect
+ reduced
movement of pest
and pathogens
Intra-specific crop diversity – pest and disease regulation
Improved ecosystem functions
Longer period of
food for pollinators
Diversity of
pollinators
supported
Increase in number
of functional traits
continuous
biomass ensured
Production system
more resistant and
resilient to
disturbance
Increased facilitative
interactions
More efficient pollination
Different
resource
acquisition
efficiency
Genotype
complement
-arity
Differing
architecture
reduces stress to
other genotypes
Pollinator sharing
attraction
Cost effectiveness?: Increasing crop genetic diversity versus increasing landscape heterogeneity
Intra-specific crop diversity (Pollination)
Improved ecosystem functions
Longer period of
vegetation
coverage
Increased N-
Fixation
Improved soil
processes
Reduced soil
erosion
Increase in number
of functional traits
continuous
biomass ensured
Production system
more resistant and
resilient to
disturbance
Increased facilitative
interactions
Improved soil processes
(soil formation; N-
fixation; organic matter)
Different
resource
acquisition
efficiency
Genotype
complement
-arity
Differing
architecture
reduces stress to
other genotypes
Decomposition
and nutrient
cycling
Intra-specific crop diversity – soil and nutrient processes
Intra-specific crop diversity – CO2 sequestration
Improved ecosystem functions
longer period for
CO2 sequestration
more efficient
CO2
sequestration
CO2
sequestration
Increase in number
of functional traits
continuous
biomass ensured
Production system
more resistant and
resilient to
disturbance
Increased facilitative
interactions
Jarvis et al., in preparation