Agronomy Cheat Sheet 2026

The 30 highest-yield Agronomy facts, distilled from real exam questions. Print it, save it as a PDF, or study it here — free, no sign-up.

1. What role do mycorrhizal fungi play in plant nutrition? → Extend root surface area for nutrient uptake
2. Which crop is classified as a C3 plant? → Wheat (Triticum aestivum)
3. The law of the minimum, attributed to Justus von Liebig, states that: → Growth is limited by the nutrient present in the least relative amount
4. Which of the following crops may be grown without irrigation? → Millets
5. What is the field capacity of a soil? → The soil water content after free drainage has ceased following saturation
6. In corn production, what is the 'critical period for weed control'? → V1 to V8 growth stages when weeds compete most for resources
7. What does 'mode of action' refer to for a herbicide? → The biochemical pathway or enzyme in the plant the herbicide disrupts
8. Open-pollinated varieties differ from hybrid varieties primarily because they do what? → Breed true from saved seed and maintain genetic consistency
9. The concept of 'evapotranspiration' (ET) in agronomy combines which two processes? → Soil evaporation and plant transpiration
10. Which of the following crops can withstand draught better? → Cowpea
11. What is the microbial process that converts organic nitrogen in soil organic matter into plant-available ammonium (NH4+)? → Ammonification
12. Which of the following is a common method for measuring soil moisture in irrigated fields? → Tensiometer
13. Soil salinity is measured using which instrument or method? → Electrical conductivity meter
14. Which of the following is classified as a legume crop? → Soybean
15. Which soil order is commonly found in the Corn Belt and is highly productive for agriculture? → Mollisol
16. Which cultural practice is most effective at slowing the development of herbicide-resistant weed populations? → Rotating herbicide modes of action and integrating non-chemical weed control
17. What is 'cation exchange capacity' (CEC) a measure of in soil science? → The soil's ability to retain positively charged nutrient ions
18. What is the primary function of phosphorus in plant metabolism? → Energy transfer via ATP
19. Which USDA zone of crop pest reporting helps agronomists track insect migration patterns? → Cooperative Agricultural Pest Survey (CAPS)
20. What is an 'economic threshold' in pest management? → The pest density at which control action must be taken to prevent economic loss
21. Which cover crop is most commonly used to add nitrogen back to the soil? → Hairy vetch
22. Which environmental factor does NOT directly drive stomatal opening or closing? → Soil pH
23. In sprinkler irrigation design, what does 'distribution uniformity' measure? → How evenly water is applied across the irrigated area
24. What is the primary advantage of using certified seed over saved farm seed? → Guaranteed genetic purity, germination rate, and freedom from weed seeds
25. What does the term 'quantitative trait' mean in plant genetics? → A trait controlled by many genes showing continuous variation
26. What is the main purpose of a grassed waterway in a crop field? → Safely convey concentrated surface runoff without causing erosion
27. What is the net ATP yield per glucose molecule during complete aerobic cellular respiration? → 36–38 ATP
28. Which tillage practice leaves at least 30% crop residue on the soil surface? → Conservation tillage
29. Which gas is fixed by nitrogen-fixing bacteria in legume root nodules? → Atmospheric nitrogen (N₂)
30. Potassium deficiency in crops typically first appears as what symptom? → Marginal leaf scorch on older leaves