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The role of nitrogen in agricultural production systems
Answers
- Write notes in your own words to summarise each of the five conversion processes that are described.
Ammonification: conversion of organic nitrogen to ammonium (NH4+) by a range of soil living bacteria and fungi. The bacteria and fungi get carbon and energy from the breakdown of organic matter, while ammonium is released (1).
Nitrification: ammonium (NH4+) is converted to nitrite (NO2-) and then to nitrate (NO3-) by a small number of soil organisms. These organisms are autotrophic, gaining their energy from the conversion of NH4+ to NO2- while any needed carbon is obtained from CO2 (2).
Denitrification: the conversion of nitrites (NO2-) and nitrates (NO3-) into gaseous N and are removed from the soil system. Denitrification occurs mainly when there is little or no oxygen in the soil, such as when the soil is waterlogged (3).
Nitrogen fixation: conversion of nitrogen gas (N2) to ammonium (NH4+) either by free-living bacteria in soil or water, or by bacteria in symbiotic relationship with plants, e.g. legumes (4).
Nitrogen immobilization: nitrogen is incorporated into the microbial cells and tied up in the microbial pool of nitrogen (5).
- Identify each process on the nitrogen cycle diagram below, using the appropriate numbers 1-5.
See the diagram below.
- Include the processes of leaching and volatilisation to your notes, giving them the numbers 6 and 7 respectively.
Leaching: downward movement of dissolved nitrogen through the soil profile carried by infiltrating water (6).
Volatilisation: losses of ammonia (especially in fertilisers) from the soil surface to the atmosphere (7).
Then see the diagram below.
- Colour code the arrows on the nitrogen cycle diagram to show and differentiate between the inputs to and losses of nitrogen from the cycle. Make sure you include the harvest of plant and animal material.
See the diagram below.
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