Plant and Soil Science
Domain 3: Plant and Soil Science
This domain tests plant anatomy and growth, photosynthesis, soil formation and texture, soil pH and fertility, nutrient management, pest management, and crop production practices. Expect calculations involving seeding rates, soil amendments, and interpretation of soil test reports.
Core rules and concepts
- Photosynthesis converts light, water, and carbon dioxide into sugars; respiration releases energy. Transpiration moves water through the plant.
- Soil texture is classified by sand, silt, and clay percentages using the soil texture triangle. Clay holds more water and nutrients than sand.
- Soil pH affects nutrient availability. Most crops grow best near pH 6.0-7.0; legumes such as alfalfa need higher pH than many grasses.
- Essential nutrients include macronutrients (N, P, K, Ca, Mg, S) and micronutrients. Legumes fix nitrogen through rhizobia, so they usually need little or no nitrogen fertilizer.
- Integrated pest management uses scouting, thresholds, cultural practices, biological controls, and judicious pesticide use.
Worked example
A seed lot is 90% pure and 80% germinates. Pure live seed (PLS) = 0.90 × 0.80 = 0.72, or 72%. If the recommendation is 120 lb PLS per acre, bulk seed needed = 120 ÷ 0.72 = 166.7 lb/acre. The reasoning is to divide the desired PLS rate by the PLS fraction, not multiply, because only 72% of the bulk seed is viable.
Traps that cost marks
- Applying nitrogen to a healthy legume stand instead of recognizing nitrogen fixation.
- Confusing soil pH with soil fertility; a high pH does not guarantee adequate nutrients.
- Using bulk seed weight as if it were all viable seed.
- Treating clay and sand as having the same water-holding capacity.