The document discusses various factors affecting agricultural yield, including climatic elements such as temperature, precipitation, humidity, and soil conditions. It highlights the importance of resistance to environmental stress, and interactions among crops, soil properties, and atmospheric gases in contributing to plant health and productivity. Additionally, it addresses the challenges faced by farmers due to economic conditions and lack of resilient crop varieties.

1. K.VANANGAMUDI
Formerly Dean (Agri.), TNAU
Dean, Adhiparasakthi Agricultural College, Kalavai
Professor & Head, Seed Science & Technology
Tamil Nadu Agricultural University,
Coimbatore, Tamil Nadu

3. • Resistance to lodging
• Tolerance to drought, salinity, flood, pests and
diseases
• High yielding capacity
• Chemical composition of grains (Oil and protein)
• Quality of grain (Fineness, coarseness) and straw
(Sweetness, Juiciness)

4. Climatic factors
• 50% of yield is attributed by climatic factors

5. 1. Precipitation
• Includes rainfall, snow, hail, fog and dew.
• In heavy and evenly distributed rainfall areas –
Rice in plains
Tea, coffee and rubber at higher elevation
• In low and uneven distributed areas, dry farming
is common
• Drought resistant crops - Pearl millet, sorghum,
minor millets and pulses

6. 2. Temperature
• Measure of intensity of heat
• Crops need range of temperature:15-40˚C

7. Temperature for different crops
Crops Minimum
temperature
(°C)
Optimum
temperature
(°C)
Maximum
temperature (°C)
Rice 10 32 36-37
Wheat 4-5 20 30-32
Maize 8-10 20 40-43
Sorghum 12-13 25 40
Tobacco 12-14 29 29-35

8. 3. Atmospheric humidity (RH)
• Invisible water in air
• RH – Ratio between amount of moisture present in
air to saturation capacity of air at particular
temperature.
• Measured by thermo hygrograph or Psychrometer
• Optimum RH for most of crops: 40-60%
• High RH - Outbreak of pests and diseases.

9. 4. Solar radiation
• PAR – Photosynthetic active radiation: 400-700
nanometers – Optimum for crop production
• Phototropism – Plant response to light direction
 Eg. Sunflower
• Photo intensive – Season bound

10. Photoperiodism
Plant response to day length

11. Photoperiodism
• Examples
• Short day
Eg. Rice, sunflower, cotton
• Long day
Eg. Barley, oats, carrot, cabbage.
• Day neutral
Eg. Tomato, maize

12. 5. Wind velocity
• To carry moisture, precipitation and heat
• Suitable wind movement: 4-6 km/ hr

13. 6. Atmospheric gases
• CO2 – 0.0407%
• O2 – 21% (20.95)
• N2 – 78.8% , Argon – 0.93% and Others – 0.02%
• CO2 – Essential for Photosynthesis
• O2 – Essential for Respiration
• Nitrogen fixation
 Symbiotic (Rhizobium)
 Non symbiotic free living bacteria (Cyanobacteria, Azotobacter)
• N - Also supplied by lightning and rainfall
• SO2, CO, CH4, chloro fluoro carbons- Toxic to plants.

14. Q & A
 Photosynthetic active radiation essential for carbohydrate
production is
a. 0.4-0.7µ b. 0.2-0.3µ
c. 0.3-0.5µ d. 0.7-0.9µ
 Oxygen content in atmosphere is about
a. 20% b. 20.95%
c. 21% d. 20.87%
 Example of short day plant is
a. Rice b. Maize
c. Barley d. Oats
 Associative Symbiotic N-fixer is
a. Rhizobium b. Azospirillum
c. Azotobacter d. Mycorrhiza

15. 1. Soil moisture (water)
• Helps in chemical and biological activities of soil
including mineralization.
• Moderates soil temperature
• Regulates availability and mobility of nutrients.
• Moisture is more in clay soil than sandy soil.

16. 2. Soil air
• Rice needs low level of oxygen due to water logging
condition.
• High O2- Potato, tobacco, cotton, linseed, tea, legumes
3. Soil temperature
• Affects physical and chemical process of soil
• Regulates absorption of water and nutrients.

17. 4. Soil mineral
• Sources of plant nutrients like Ca, Mg, S, Mn, Fe,
K
5. Soil organic matter
• Supplies major and micro nutrients.
• Improves soil texture.
• Increases water holding capacity.
• Source of food for microorganism

18. 6. Soil organisms
• Helps in decomposition of raw organic matter
• N2 fixation by microbes
7. Soil pH - Soil reaction
• Low pH soil is injurious to plant, due to high iron
and aluminium toxicity.

20. 1. Plants
• Competition for moisture, nutrients, sunlight.
• Complementary effect or synergistic effect.
Eg. Cereals and legumes.
• Competitive crops
Striga in sorghum and sugarcane
Orobranche in tobacco
Cuscutta in lucerne

21. 2. Animals
• Soil fauna: Protozoa, nematodes, snails, insects.
• Insects and nematodes causes crop damage
• Honey bees and wasp helps in pollination
• Borrowing of earth worms helps
 Aeration
 Drainage
 Organic matter decomposition
• Large animal cause damage to crops.
• Eg. Animal grazing

23. • Topography - nature of the surface earth (Leveled
and slope)
• Increase in latitude decreases the temperature and
precipitation.
• Steep slope - Favours run off and loss of top soil
(Nutrients)
• Slope exposed to low intensity of light and strong
wind results in poor yield.

24. • Inclination towards farming
• Land holders choose only food and fodder crops
• Non availability of resistance varieties drought,
pest and disease
• Economic condition of farmers: Marginal,
medium and small farmers find inability in
resource mobilization.

25. Q & A
 Synergistic effect is observed in
a. Cereals and legumes
b. Cereals and weeds
c. Sugarcane and Striga
d. Both b and c
 Crops requiring higher oxygen content is
a. Sugarcane b. Cotton
c. Legumes d. Both b and c
 Low and uneven rainfall is a common in
a. Semi arid b. Dry land farming
c. Wetland farming d. Garden land