CROP PRODUCTION Unit 3: Crop Physiology

Physiology (71) The study of plant functions and responses of crops grown in ag environments

Yield (71) Yield: maximum amount of product produced per unit of land area –Grain: typically measured in bushel/acre –Forage: measured in tons/acre Two types of yield: –Biological Yield: total dry matter produced per plant or unit area (leaf, stem, grain, etc.) –Economic/Agricultural Yield: volume or weight of plant parts with marketable value Yield = (plants/area) x (heads/plant) x (seeds/plant) x (weight/seed)

Rate of Growth (72) Rate of Growth: follows a general pattern altered by environmental factors Growth Curve: three phases 1.Logarithmic phase: ever-increasing rate of growth 2.Linear phase: constant growth rate 3. Maturation phase: growth slows & declines with age Logarithmic Linear Maturation

Rate of Growth (72) Plant growth regulators –Auxins—cell elongation (indoleacetic acid (IAA) - #1 on right) –Gibberellins—cell elongation; act differently than auxins (gibberelic acid - #2 on R) –Cytokinins—cell division & differentiation, etc. (zeatin - #3 on R) –Growth inhibitors—induce dormancy in seeds & plants (abscisic acid (ABA) - #4 on R) –Ethylene—considered growth inhibitor— hasten fruit ripening, etc.

Rate of Growth (73) Measuring Growth Rates: estimated by measuring the progression of length or weight over time—experiment results Regrowth: –Damage caused by frost, wind, hail, insects, animals, machines –Species, age, and size of the plant determines whether the plant will regrow –Cereal crops—no lateral buds, one point on stem –If growing point is injured or removed, regrowth can be completely blocked or reduced

Photosynthesis (77) The use of the sun’s energy to convert inorganic compounds into sugars 6CO 2 + 6H 2 O = C 6 H 12 O 6 + 6O 2 –In the presence of light energy –Occurs in chloroplasts

Respiration (78) Respiration: oxidative breakdown of organic substances –C 6 H 12 O O 2 = 6CO 2 +6H 2 O + ATP (energy) –Occurs in mitochondria Synthesis: energy released from respiration is used to synthesize more complex materials

Photosynthesis (78) Net photosynthesis (Pn): aka Net Assimilation Rate (NAR) –Stored energy from photosynthesis—energy released from respiration –Increased by genotype, leaf area, and leaf orientation –Decreased by shading and water/mineral deficiencies

Photosynthesis (78) Leaf Area Index (LAI): example of crop with LAI of three Total leaf area of crop plants = 3 ha. of crop leaf surface Soil surface area occupied by plants 1 ha. of ground Canopy: space above the soil surface occupied by aerial portion of the plant

Photosynthesis (79) Photosynthetic efficiency: energy conversion process where solar energy is converted to chemical energy –Light Quality: wavelengths that are most effective in photosynthesis Best: nanometers (about 40% of total solar radiation hitting leaf) Why do plants look green? Wavelengths in green are not effectively absorbed by chlorophyll and are reflected, making the plants appear green

Photosynthesis (80) Light interception: –Plant spacing: increase yield by increasing photosynthesis or decreasing respiration Arrange plants in a pattern to intercept more light Leaf pattern also increases interception of upright leaves –Leaf angle: soybean leaf attains maximum rate of photosynthesis at about 50% of full sun All plants utilize low-intensity light more efficiently Upright leaves in corn can cause yield increase of 40% and reduce barrenness by 50%

Photosynthesis (82) Carbon dioxide concentration: influences photosynthesis –Normal air contains 0.034% CO 2 (340 ppm) –C3 or C4 pathways (based on first stable product of the pathway)

Transport and Uptake (83) Translocation: movement of organic and inorganic solutes from one part of the plant to another Transpiration: loss of water from plant tissues in vapor form –Two functions: evaporation and cooling –Evapotranspiration: total water loss in a canopy Water loss from crops by transpiration Water loss from soil by evaporation

Transport and Uptake (85) Water requirement (aka evapotranspiration ratio)/units of water required to produce a unit of plant dry matter WR = (kg water evapotranspired)/kg dry matter Complete table from page 85

Transport and Uptake (85) Mineral uptake –Methods of root-nutrient contact: Root growth and interception of nutrients Nutrient flow in soil water Diffusion of nutrients from high concentration to low concentration –Roots absorb nutrients in two ways: Passive uptake: transpiration is essential driving force—nutrient ions move w/H 2 O into roots Active intake: nutrient ions pumped into roots using ATP energy

Transport and Uptake (86) Mineral uptake –Factors influencing nutrient uptake Reduced root growth Nutrient concentrations in the root zone Adequate soil aeration and moisture

Transport and Uptake (87) Biological nitrogen fixation –Proteins = nitrogen + carbohydrates –Atmosphere 80% nitrogen –Plants cannot use nitrogen from the air, it must be “fixed” –Soybeans fix own nitrogen in nodules containing Rhizobium bacteria located on the nodules –Some species of grass can fix small amounts of nitrogen, through relationship with Azospirillium –Relationship that mutually benefits both organisms is known as symbiotic (symbiosis) Plants provide energy (carbs) to bacteria; bacteria provide N

Crop Plant Responses (88) Germination: items required for germination: water, temperature, oxygen, and light Etiolation: elongation of plants grown in the dark or low light; causes include: –Shady conditions –High populations –Increased levels of auxins (plant growth hormones), esp. indoleacetic acid (IAA) –Sunlight destroys IAA

Crop Plant Responses (89) Tillering: producing secondary stems from the crown root area; increased by cool temperatures, soil fertility, and soil moisture; decreased by low IAA levels Branching and barrenness: also affected by levels of IAA

Crop Plant Responses (89) Crop Development –Reproductive Determinate growth type: most vegetative growth is done before flowering—wheat, oats, corn Indeterminate growth type: vegetative growth and reproductive stages overlap—alfalfa, trees, other perennials Semideterminate growth type

Crop Plant Responses (90) Crop Development –Time of flowering and photoperiodism: Photoperiodism: effect of photoperiod on flowering and plant maturity Photoperiod: length of daylight in a 24 hour period –Long day plants—flower when minimum daylight length is reached –Short day plants—flower maximum daylight length is not reached –Day neutral plants—flowering response is insensitive to day length

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