Environmental Factors Affecting Crop Production

Solar Radiation

• Electromagnetic energy from the sun

• Provides light and heat for the Earth and energy for photosynthesis

visible (42043%) and infrared light (52-55%), with only a small fraction consisting of

ultraviolet radiation.

Most solar radiation reaching Earth’s surface comprises:

Photosynthetically Active Radiation (PAR)

portion of the electromagnetic spectrum that photosynthetic organisms, like plants and algae, can utilize for

photosynthesis. This specific range of light wavelengths, typically between 400 and 700 nanometers (nm), corresponds to visible light

Tropics are warmer than the poles

Solar radiation varies with latitude

Earth’s tile causes seasons

Different areas get varying solar radiation throughout the year

Impact on the biosphere

Solar energy powers photosynthesis and food webs

Albedo

• is the ratio of reflected solar radiation to incident solar radiation

• different surfaces have different albedos (range is from 0-1)

• Earth’s average albedo is 0.30, meaning that roughly 30% of incoming solar radiation is reflected back into space

Solar Constant

• represents the total amount of solar energy that would be received by a surface at a perpendicular angle to the sun’s rays, at the average distance between the Earth and the Sun

• the mean solar constant is 1,367.5 W/m2

Solar Constant

determines the amount of solar energy reaching Earth’s upper atmosphere

Albedo

determines how much of that energy is reflected

back to space

Changes in albedo

such as those caused by melting ice or changes in cloud cover can significantly impact Earth’s climate

Lower albedo (more absorption)

leads to higher temperatures

higher albedo (more reflection)

leads to lower temperatures

[(1-Albedo Factor)x Solar Constant] / 4.0

Earth Emitted Energy

Solar radiation

provides light for photosynthesis but also heat energy that warms that environment.

Temperature patterns

largely driven by the distribution and absorption of solar radiation.

light and temperature

interconnected factors affect crop growth and

development.

below the optimal

when temperature is (_) warming can increase yields

beyond the optimal

warming pushes in the temperature (_), yields are negatively impacted

Minimal Temperature

lowest temperature where growth can still occur

Optimum Temperature

range where growth processes are most efficient

Maximum Temperature

upper limit beyond which growth is impaired or stopped

Growing Degree Days

accumulated temperature units above a base (minimum) temperature threshold that predict plant developmental stages like flowering and maturity

[(Max temp) + (Min temp)/2] – base temp

Growing Degree Days

Growing Degree Days

Tool to measure heat accumulation – “temperature clock”

Hydrologic Processes

cycle involves evaporation from land and evaporation from terrestrial vegetation driven by solar energy, cloud formation, and precipitation.

Rainfall

most important climatic element in the Philippines.

Rainfall

distribution throughout the country varies from one region to another, depending upon the direction of the moisture-bearing winds and the location of the mountain systems.

water

critical for photosynthesis, nutrient transport, cell expansion, and temperature regulation.

Deficiency (drought)

• reduced stomatal conductance -> reduction in photosynthesis

• poor germination, stunted growth, smaller leaf area lower flowering, fruit set and grain filling

• yield loss is often non-linear and irreversible once critical stages are affected

Excess (flood/waterlogging)

• oxygen deprivation in roots -> root rot, reduced nutrient uptake

• increases susceptibility to diseases and leaching losses

• delays maturity and harvest; may reduce grain quality

Water stress during critical stages (e.g., flowering, grain filling) causes maximum yield reduction

Timing Matters

Relative Humidity

amount of water vapor in the air versus what it can hold

Vapor Pressure Deficit

amount of moisture in the air and how much moisture the air could potentially hold when its saturated

high VPD (>1.0 kPa)

air can still hold a large amount of water (large gradient between a plant and the air)

Low VPD

• Low Transpiration

• High Plant Growth

• High Nutrient Uptake

• Low Shoot Nutrient

• Low Root Nutrient Uptake Rate

Low precipitation and high air moisture

force plants to close their stomata (wilting point), which drastically reduces cooling via evapotranspiration (ET), thereby converts energy into sensible heat, accelerating the rise in canopy temperature and moisture demand, thereby reinforcing the heat and drought stress

thigmomorphogenesis

plants exposed to wind may grow shorter, sturdier, with altered tissue properties for better mechanical support

Wind and Wind Direction

• Mechanical Stress: stem bending, leaf tearing, and in severe cases, structural failure (e.g., lodging in cereals).

• Physiological Impacts: Increases transpiration and evaporative demand, influencing water use efficiency and stomatal behavior.

• Yield and Economic Losses: Lodging can significantly reduce grain yield and quality in crops like wheat, rice, and maize; losses may reach up to 80% under severe events.

• Management Strategies: Windbreaks, denser planting, varietal selection, and agronomic practices (e.g., growth regulators) help mitigate wind damage.

laminar boundary layer to a turbulent one due to the canopy's friction and structure

enhances the movement of water vapor away from the leaf surfaces. Consequently, the turbulent flow increases transpiration and evaporative demand on the plant, which directly influences its water use efficiency and stomatal behavior.

Climate

average pattern of weather over a long period (typically over 30 years or more) in a particular regions

Weather

short-term atmospheric conditions in a specific location at a given time. Include temperature, humidity, rainfall, windspeed and direction, cloud cover, air pressure

• tropical and maritime

• high temperature, high humidity and abundant rainfall

• Temperature, humidity, and rainfall are the most important elements

Climate of the Philippines

• High solar radiation, warm (hot!!!) temperatures year-round

• Distinct wet and dry seasons rather than four-season temperate model

Characteristics of tropical climates

Humid tropics (annual rainfall of >2000 mm, distribute over a long rainy season)

Agroecological zones

mixture of organic matter, minerals, gases, water, and

organisms that together support the life of plants and soil

organisms

Soil

• Physical - Color § Texture § Structure

• Chemical - pH § Nutrients § CEC § Salinity

• Biological - Soil microbes § Biological processes

occurring in the soil

Soil Properties

indicates some general properties of the soil, as well as

some chemical processes occurring beneath the soil surface.

Soil color

result of the accumulation of certain soil

components, e.g., iron, organic matter, or salts.

Soil Color

reflection of its age and temperature and moisture characteristics of the climate.

Soil color

• High in organic matter → improves structure, water retention, and nutrient cycling

• Supports high yields and microbial activity

Dark Brown to Black

• Rich in iron (Fe), but low in phosphorus (P) due to fixation

• Red = well-drained, low OM;

• Yellow = poor aeration

• Generally low fertility; needs careful management

Red or Yellow

• Indicates prolonged flooding → Fe reduction releases P

• After drying, re-oxidized Fe fixes more P → lower fertility over time

• Supplemental P still needed for crops like rice

Gray

• Low OM and nutrients; often sandy or salty

• High salts can limit water uptake and cause P deficiency

White or Light Gray

Soil Texture

refers to the way moist soil feels when touched,

such as coarse, smooth, or gritty.

Soil Texture

describes the relative proportions of different particle sizes, including sand (largest particle), silt (medium- sized particle), and clay (smallest particle), within the soil.

Soil Structure

refers to the way soil particles group together to form aggregates or peds

Granular

individual soil particles grouped together in small, nearly spherical grains

Blocky

soil particles that cling together in nearly square or angular blocks having more or less sharp edges

Prismatic

soil particles which have formed into pillars separated by vertical

cracks

Platy

made up of soil particles aggregated in thin plates or sheets piled horizontally on one another

Soil pH

affects both nutrient availability and interactions among nutrients.

• many nutrients become less available, while Fe, Al, and Mn can reach toxic levels.

• elements may also displace other cations from

  clay or humus colloids

low pH

• calcium can tie up phosphorus

• elements like molybdenum (Mo) and boron (B) may become toxic in some soils.

• (pH above 5) Aluminum becomes insoluble and phosphorus binds to Fe/Al oxyhydroxides, reducing its availability

high pH

Cation Exchange Capacity (CEC)

measure of a soil’s ability to hold and exchange positively charged ions (cations) such as potassium (K+), calcium (Ca2+), magnesium (Mg2+), and ammonium (NH4+)

High CEC soils

can retain more nutrients and supply them steadily to plants (e.g., clay-rich or organic soils)

Low CEC soils

have limited nutrient-holding capacity and are prone to nutrient leaching (e.g., sandy soils)

Cation Exchange Capacity

influences soil fertility, fertilizer efficiency, and soil buffering

capacity (resistance to pH changes).

Soil biological properties

refer to the presence and activity of living organisms in the soil, including bacteria, fungi, protozoa, nematodes, and earthworms. These organisms play key roles in

• nutrient cycling,

• organic matter decomposition,

• soil structure formation, and

• plant health.

Solvita Respiration Test

determines the CO2 level given by the soil or soil respiration, the higher the reading, more respiration/biological activity

• soil till is 2.5

• no-till reads 4

Upland farming and deforestation cause topsoil loss,

reducing fertility and crop yields.

Erosion

Continuous cropping without replenishment leads to

declining N, P, K levels.

Nutrient Depletion

~70% of soils are acidic, causing nutrient lock-up and

aluminum toxicity.

Acidification

Forest conversion and intensive tillage reduce soil structure and water retention.

Organic Matter Loss

Industrial waste and wastewater use lead to heavy

metal and pathogen buildup.

Contamination

Poor irrigation and overuse of machinery affect

water uptake and root growth.

Salinization and Compaction

Typhoons and droughts worsen degradation and

disrupt soil microbial activity.

Climate Stress

Soil Erosion

Gradual process that occurs when the impact of water

or wind detaches and removes soil particles, causing

the soil to deteriorate

• A geological process: dislodgement, transportation, and deposition

In tropical countries like the Philippines, pests, diseases, and weeds are more common because of the warm and humid climate.

• This makes it even more important to choose the right variety.

• A good variety is one that can resist common biotic stresses, grow well in the local environment, and fit into the existing farming system.

Why choosing the right variety matters?

Variety

specific type of crop with a defined set of traits—like yield potential, resistance to pests, or tolerance to drought.

seed

basis of genetic potential.

Good seedlot

strong start, healthy crop

Poor seedlot

weak growth, low resilience

Pests and Diseases

• Insects

• Pathogens

• Nematodes

Weeds and Competition

• Noxious and parasitic weeds

• Allelopathic effects

• As alternate host to pests and diseases

Animal and Human Activities

• Grazing, trampling

• Pollution, Peace & Order

• Crop Production Practices

Biotic Factors

In the Philippines, an estimated 37% of crops are lost annually due to pests (varies largely depending on region), with yield losses of 15% or more possible without proper management.

Major pests include

• rice brown planthopper,

• corn borer,

• banana aphids, and

• mango leafhopper.

Additionally, diseases like brown spot, deadheart, leaf blast, and sheath blight can significantly impact rice yields.

Crop Losses Due to Pests

plants that compete with crops for nutrients, light, and water. They can also obstruct irrigation, harbor pests, and transmit diseases.

Weeds

• Land usage (for example, plant type) and sources of pollution (for example, fertilizers) perturb microbial community composition and function, thereby altering natural cycles of carbon, nitrogen and phosphorus transformations.

• Methanogens produce substantial quantities of methane directly from ruminant animals (for example, cattle, sheep and goats) and saturated soils with anaerobic conditions (for example, rice paddies and constructed wetlands).

• Human activities that cause a reduction in microbial diversity also reduce the capacity for microorganisms to support plant growth.

Agriculture and other human activities

that affect microorganisms.