AGRI 103: Agronomy - Weather and Climate

AGRI 103: Agronomy - Weather and Climate

Climate Overview

  • Climate Definition: Typical long-term conditions in a region.

    • Influenced by:

    • The pattern of the sun’s energy distribution on Earth.

    • Topographic features including bodies of water, landforms, and elevation.

    • Air masses.

  • Saskatchewan Climate:

    • Classified as temperate: Positioned between tropical and polar regions.

    • Distinct seasonal changes: Recognizable winter and summer seasons.

    • More specifically categorized as a semi-arid region.

    • Receives 25-51 cm of annual precipitation.

Biome Distribution

Whittaker biomes


Refer to Figure 3.2 that depicts biomes based on Mean Annual Temperature and Precipitation (Ricklefs, 2008, adapted by Myrna Simpson).

  • Biomes include:

    • Tundra

    • Boreal forest

    • Temperate seasonal forest

    • Temperate rain forest

    • Tropical rain forest

    • Tropical seasonal forest/savanna

    • Subtropical desert

    • Temperate grassland/desert

    • Woodland/shrubland

Weather Overview

  • Weather Definition: Deals with short-term atmospheric conditions.

  • Key Features:

    • Precipitation and temperature are critical factors affecting crop growth.

    • These factors influence the types of crops that can be successfully cultivated in a given area, particularly under constraints related to temperature and precipitation patterns.

  • Importance of measuring annual precipitation for agriculture.

Water and Crop Growth

  1. Water's Role in Plants:

    • Constitutes 75-90% of plant mass.

    • Facilitates critical functions such as:

    • Providing turgor pressure.

    • Acting as a solvent and transportation medium for nutrients (minerals and sugars).

    • Being a component in various chemical reactions.

    • Serving as a coolant through transpiration.

Measuring Crop Water Requirements

  • Evapotranspiration:

    • Definition: The collective process of water transforming from liquid to gas through evaporation and transpiration.

    • Variability: Changes with the growth stage of plants and air temperature.

    • Different crops exhibit unique water use rates.

  • Crop Water Use Efficiency (WUE):

    • Definition: The amount of water required to produce an equal quantity of dry matter.

    • Variation: Different crops display differing WUE ratings.

Water Use Efficiency Metrics

  • Example Data: Comparison of water use efficiency (WUE; measured in kg ha$^{-1}$ mm$^{-1}$) in various crops, including winter wheat and green peas at the Columbia Basin Agricultural Research Center (CBARC), Pendleton, OR, based on 7-year means (1977–1982 and 1985).

Extremes in Precipitation

  1. Drought:

    • Definition: A prolonged period of insufficient precipitation leading to soil moisture deficiency for crops.

    • Effects:

    • Moisture deficit impacts on crops are exacerbated by high temperatures that increase evapotranspiration rates.

  2. Flooding:

    • Definition: Excess water accumulation in landscapes, resulting in standing water, especially in high water table or poorly drained soil regions.

    • Consequences:

    • Soil air spaces fill with water, leading to inadequate root respiration.

    • Impairs nutrient uptake due to anaerobic conditions, causing many crops to exhibit poor growth or die.

    • Injury extent from flooding depends on several factors including duration, air and water temperature, and the plant's growth stage.

  3. Soil Health Issues with Flooding:

    • Increased risk for soil-borne root and crown diseases.

    • Potential nitrogen fertilizer loss due to leaching and denitrification processes in saturated soils.

Temperature and Crop Growth

  1. Temperature Impact:

    • Significant effect on physical and biochemical processes in plants:

    • Affects water state (solid, liquid, gas) within the plant.

    • Influences flow rate (viscosity) of water.

    • Impacts reactivity in chemical reactions, with enzymes showing optimal temperature ranges.

    • High temperatures can denature enzymes, hindering plant function.

  2. Temperature Extremes:

    • Freezing Injury:

    • Ice formation within cells damages membranes and organelles.

    • Chilling Injury:

    • Disruption of membrane integrity under cold conditions.

    • Heat Injury:

    • Excessive heat disrupts metabolic processes, potentially causing cell collapse.

  3. Observed Symptoms in Plants Due to Thermal Stress:

    • Purpling, cupping, and nutrient deficiencies following exposure to extreme cold or heat.

    • Impacts from high temperatures can lead to aborted flowers in crops, resulting in below-normal yield potential.

Plant Species Temperature Responses

  • Each species has an optimum temperature range for growth; deviations can result in suboptimal physiological performance.

  • Table 10-3: Minimum, optimum, and maximum growth temperatures for various temperate and tropical plant species (adapted from Decoteau, 2005).

    • Temperate Cool-season Plants (e.g., wheat, alfalfa):

    • Min: 41°F (5°C)

    • Optimum: 59-86°F (15-30°C)

    • Max: 95-104°F (35-40°C)

    • Tropical Warm-season Plants (e.g., corn, soybean):

    • Min: 50°F (10°C)

    • Optimum: 86-95°F (30-35°C)

    • Max: 113°F (45°C)

Latitude and Seasonal Effects

  • Latitude Impact: Distance from the equator plays a critical role in determining the length of growing seasons or the number of frost-free days.

    • Defined as the span from the last killing frost in spring to the first killing frost in fall.

Crop Selection and Adaptation to Temperature

  • Crops Classification: Based on their region of origin or optimal temperature requirements:

    • Temperate Crops: Typically grown in areas with marked seasonal temperature changes. Examples include wheat and barley, which thrive in spring and fall while becoming semi-dormant during summer heat.

    • Tropical Crops: Prefer warm climates and include crops like corn and soybean.

Variety Selection Based on Temperature Adaptation

  • Variation within Crop Species: Individual varieties display different tolerances to temperature extremes.

  • Breeding Focus: Development of varieties and hybrids with varying maturity rates tailored to specific frost-free growing periods of regions.

    • Relative Maturity: Indicates the average days required to reach physiological maturity. Selecting appropriate varieties maximizes the use of environmental resources for grain production ahead of the first killing frost.

    • Variation in maturity is often prioritized over cold tolerance in breeding decisions, emphasizing adaptability to local climates.