Key Formulas & Equations
Respiration: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy
Transpiration Ratio: TR = water lost / CO₂ gained
Leaf Area Index: LAI = total leaf area / ground area
Evapotranspiration: ET = Kc × ET₀
Irrigation Requirement: IR = ET - effective rainfall
Soil Water Content: θ = (wet weight - dry weight) / dry weight × 100%
Population Density: Plants/ha = 10,000 / (row spacing × plant spacing)
Seed Rate: Seed rate (kg/ha) = (Target population × 1000-seed weight) / (germination% × field emergence%)
Crop Yield: Yield = population × grains/plant × grain weight
Compost C:N Ratio: C:N = total carbon / total nitrogen (ideal = 25-30:1)
Core Concepts
Soil Science
Study of soil formation, classification, and mapping. Includes soil physics (texture, structure), chemistry (pH, nutrients), and biology (microorganisms, organic matter).
Plant Physiology
Study of plant functions: photosynthesis, respiration, transpiration, nutrient uptake, and growth regulation. Understanding these processes is key to crop improvement.
Agronomy
The science of crop production and soil management. Includes crop rotation, tillage, irrigation, fertilization, and integrated pest management.
Animal Husbandry
The breeding, feeding, and care of livestock. Includes nutrition, reproduction, health management, and welfare for cattle, poultry, sheep, and swine.
Plant Genetics & Breeding
The application of genetics to improve crop varieties. Includes hybridization, selection, mutation breeding, and biotechnology for yield, quality, and resistance.
Pest Management
Integrated Pest Management (IPM) combines biological, cultural, physical, and chemical methods to control pests economically and environmentally.
Agricultural Economics
The application of economic principles to agricultural production, marketing, and policy. Includes farm management, price analysis, and trade.
Sustainable Agriculture
Farming practices that meet current needs without compromising future generations. Includes conservation tillage, organic farming, and agroforestry.
Worked Examples
Example 1: Fertilizer Calculation
Problem: A 5 ha field needs 150 kg N/ha. Urea contains 46% N. Calculate urea required.
Solution:
Total N needed = 5 × 150 = 750 kg
Urea required = 750/0.46 = 1630 kg
Example 2: Plant Population
Problem: Maize planted at 75 cm row spacing and 25 cm plant spacing. Calculate plants per hectare.
Solution:
Plants/ha = 10,000/(0.75 × 0.25) = 10,000/0.1875 = 53,333 plants/ha
Example 3: Harvest Index
Problem: A wheat crop produces 8,000 kg/ha total biomass and 3,200 kg/ha grain. Calculate harvest index.
Solution:
HI = 3,200/8,000 = 0.40 = 40%
Practice Problems
Problem 1
Calculate water use efficiency if a crop produces 5,000 kg/ha grain using 500 mm irrigation.
Answer: WUE = 5,000/500 = 10 kg/mm/ha
Problem 2
A compost has 40% carbon and 2% nitrogen. Calculate C:N ratio.
Answer: C:N = 40/2 = 20:1
Problem 3
Calculate seed rate for wheat if target = 200 plants/m², 1000-seed weight = 40 g, germination = 90%.
Answer: Rate = (200 × 40)/(0.90 × 1000) = 8.9 g/m² = 89 kg/ha
Problem 4
Calculate ET if Kc = 1.2 and ET₀ = 5 mm/day.
Answer: ET = 1.2 × 5 = 6 mm/day
Problem 5
A field has 1.5% organic matter in top 15 cm (bulk density = 1.3 g/cm³). Calculate organic matter per hectare.
Answer: 1.5% × 1.3 × 1,500,000 = 29,250 kg/ha
Problem 6
Calculate irrigation requirement if ET = 400 mm and effective rainfall = 250 mm.
Answer: IR = 400 - 250 = 150 mm
Problem 7
Calculate LAI if total leaf area = 25,000 m² and ground area = 10,000 m².
Answer: LAI = 25,000/10,000 = 2.5