Agronomy Sustainable Agriculture and Conservation 2 — Questions and Answers
Question 1: What is nitrogen use efficiency (NUE) in crop production?
- Total nitrogen applied per acre per year
- The proportion of applied nitrogen that is taken up and used by the crop (Correct answer)
- The amount of nitrogen fixed by legumes
- The ratio of grain protein to total nitrogen in the plant
Correct answer: The proportion of applied nitrogen that is taken up and used by the crop
NUE measures what fraction of the nitrogen applied as fertilizer is actually taken up and utilized by the crop, with typical values around 50% for corn.
Question 2: Which soil conservation practice involves planting alternating strips of different crops across a slope?
- Contour farming
- Strip cropping (Correct answer)
- Terrace farming
- Windbreak planting
Correct answer: Strip cropping
Strip cropping alternates strips of row crops with close-growing crops or sod across a slope, reducing water velocity and trapping sediment eroded from row crop strips.
Question 3: What is biological nitrogen fixation (BNF) in agriculture?
- Industrial manufacture of synthetic nitrogen fertilizer
- The conversion of atmospheric N2 to plant-available ammonia by symbiotic or free-living bacteria (Correct answer)
- Soil nitrogen mineralization from organic matter
- Precipitation of nitrogen from the atmosphere in rainfall
Correct answer: The conversion of atmospheric N2 to plant-available ammonia by symbiotic or free-living bacteria
BNF is the microbial process by which certain bacteria, notably Rhizobium in legume root nodules, convert atmospheric N2 gas into ammonia available for plant nutrition.
Question 4: What is the Universal Soil Loss Equation (USLE) used to estimate?
- Annual crop yield potential
- Average annual soil erosion from rainfall and runoff on cropland (Correct answer)
- Irrigation water requirements
- Soil organic matter accumulation rates
Correct answer: Average annual soil erosion from rainfall and runoff on cropland
The USLE estimates average annual soil loss (tons/acre/year) from sheet and rill erosion on cropland based on rainfall, soil erodibility, slope, and management factors.
Question 5: Which soil health indicator is most directly improved by increasing crop diversity in a rotation?
- Soil pH
- Soil biological diversity and microbial biomass (Correct answer)
- Calcium content
- Sand fraction
Correct answer: Soil biological diversity and microbial biomass
Diverse crop rotations feed a wider variety of soil microorganisms through different root exudates and residue qualities, increasing soil biological diversity and activity.
Question 6: What is the primary environmental concern associated with excess nitrate leaching from agricultural soils?
- Soil acidification
- Groundwater and surface water contamination causing hypoxia and health risks (Correct answer)
- Depletion of soil organic matter
- Reduced crop yields from nitrogen deficiency
Correct answer: Groundwater and surface water contamination causing hypoxia and health risks
Nitrate leaches readily through soil into groundwater and streams, contaminating drinking water and contributing to aquatic hypoxia (dead zones) in water bodies.
Agronomy Sustainable Agriculture and Conservation 2
What is nitrogen use efficiency (NUE) in crop production?