ICAR AICE-JRF/SRF Nutrient Stewardship & Nitrogen Management: practice questions

1 · The global nitrogen and phosphorus cascades · medium

What does the 'nitrogen cascade' describe?

1. The stepwise increase in fertiliser prices passed down the chain from producers to farmers
2. The fall in crop nitrogen content as plants mature and leaves senesce at the end of a season
3. The flow of nitrogen fertiliser from factories to farms through a long chain of wholesale and retail dealers
4. One atom of reactive nitrogen causing a sequence of effects in air, water and soil until it is denitrified

2 · The global nitrogen and phosphorus cascades · hard

The 2015 planetary boundaries update proposed what global boundary for intentional (industrial and agricultural) nitrogen fixation?

1. About 6 Tg N per year
2. About 150 Tg N per year
3. About 62 Tg N per year
4. About 620 Tg N per year

3 · Nutrient use efficiency metrics: partial factor productivity, agronomic efficiency, recovery efficiency · medium

Why does the 15N isotope method usually give lower fertiliser recovery than the difference method?

1. The difference method counts only the grain, whereas the 15N method counts only the roots
2. Some labelled fertiliser N exchanges with soil N, so not all crop uptake of fertiliser is traced
3. The 15N isotope is radioactive and decays before the crop can take it up from the soil
4. Plants discriminate completely against 15N, so they never absorb labelled fertiliser

4 · Farm and field nutrient budgets · medium

Which budget type is used for national gross nitrogen balances published by the OECD and Eurostat?

1. Watershed export budget
2. Soil-surface budget
3. Farm-gate budget
4. Household budget

5 · Farm and field nutrient budgets · medium

A nutrient budget shows outputs exceeding inputs year after year on a smallholder farm. What does this mean?

1. Soil nutrients are being mined and fertility will decline
2. Manure is being over-applied on the farm
3. The farm is losing nutrients to water at a high rate every year
4. The farm is an ideal model needing no change

6 · The 4R framework: right source, rate, time, place · medium

Why do nitrogen rates above the economic optimum increase losses sharply?

1. Above the optimum, fertiliser granules no longer dissolve and are blown off the field by the wind
2. Above the optimum, soil microbes stop working, so all nitrogen turns into ammonia gas at once
3. Above the optimum, plants actively excrete nitrogen from their roots back into the soil solution
4. Extra nitrogen is not taken up by the crop, so it remains in soil exposed to leaching and denitrification

7 · Integrated nutrient management with organic and biological sources · medium

Long-term fertiliser experiments in India and elsewhere most consistently show that:

1. Unfertilised control plots maintain yields equal to fertilised plots over several decades
2. Nitrogen alone sustains the highest yields indefinitely with no decline at all in soil fertility
3. Farmyard manure alone always outyields balanced NPK fertiliser in every crop and soil
4. Balanced NPK with farmyard manure sustains yields and soil organic carbon better than other treatments

8 · Site-specific and sensor-based nitrogen management · medium

In site-specific nutrient management, what is an N-omission plot used to estimate?

1. The maximum yield possible with unlimited water and nutrients
2. The amount of phosphorus fixed by the soil
3. The rate of ammonia volatilisation from urea
4. The nitrogen supplied by the soil itself

9 · Enhanced-efficiency fertilisers · medium

Urea deep placement (UDP) of briquettes in puddled rice soil, widely used in Bangladesh, improves efficiency mainly by:

1. Converting urea to nitrate faster so the rice can absorb it more quickly
2. Keeping N below the surface, reducing volatilisation and runoff losses
3. Releasing nitrogen as dinitrogen gas that rice leaves absorb directly
4. Supplying phosphorus as well, because briquettes are made of rock phosphate

10 · Phosphorus legacy and peak-phosphorus debates · medium

Why do lakes often recover slowly after phosphorus inputs from farms are reduced?

1. Algae store phosphorus permanently and never release it to the water column
2. Reduced P inputs immediately increase nitrogen fixation to compensate fully
3. Phosphorus is produced in lakes by fish, so inputs of phosphorus from land do not matter
4. Legacy P in soils, ditches and lake sediments keeps releasing phosphorus for years