Agriculture Content Knowledge
The Praxis Agriculture exam samples broad, applied agriculture content rather than one specialty. Because the test publisher does not release a detailed domain breakdown, prepare across plant and soil science, animal science, agricultural business and mechanics, natural resources, and agriculture's social context. Questions typically ask you to apply a principle to a farm or classroom decision, not just recall a definition.
Core rules and concepts
- Soil pH controls nutrient availability; lime raises pH and sulfur lowers it. Cation exchange capacity (CEC) reflects a soil's ability to hold nutrients such as calcium, magnesium, and potassium; clay and organic matter raise CEC.
- Fertilizer grades are percent N, P2O5, and K2O by weight. A 50-pound bag of 10-20-10 supplies 5 lb N, 10 lb P2O5, and 5 lb K2O.
- In plants, xylem moves water and minerals upward, phloem moves sugars; photosynthesis occurs in chloroplasts. Photoperiod and vernalization trigger flowering in many crops.
- Ruminants (cattle, sheep, goats) digest fiber via rumen microbes; monogastrics (swine, poultry) depend more on concentrate feeds. Rations balance energy, protein, minerals, and vitamins.
- Integrated pest management uses scouting, economic thresholds, cultural and biological controls, and targeted pesticides to slow resistance.
- Enterprise budgets separate variable and fixed costs; break-even yield equals total costs divided by price per unit. Sprayer output (gal/acre) = 5,940 × nozzle GPM ÷ (mph × swath width in inches).
Worked example
A soil test recommends 120 lb N per acre, and the available fertilizer is urea, 46-0-0. How much product is needed? Reasoning: 46-0-0 is 46% N, so each pound of urea supplies 0.46 lb N. Divide the recommended N by the fraction: 120 ÷ 0.46 = 260.9 lb urea per acre. Check: 261 × 0.46 ≈ 120 lb N. Applying 120 lb of urea instead would supply only about 55 lb N.
Traps that cost marks
- Reading a fertilizer grade as pounds of nutrient rather than percent.
- Treating P2O5 and K2O as elemental phosphorus and potassium.
- Reversing xylem and phloem transport.
- Assuming pigs and poultry digest forage as well as cattle do.
- Diagnosing a nutrient shortage without checking soil pH.