Consider a heavily grazed pasture of fescue grass mixed with clover (clover is a legume) on a spring day. Assume it has not rained for several days and the soil has drained below field capacity.
(Remember that cattle not only consume grass, but also destroy some by walking on it; and they also produce waste which influences the Nitrogen concentration in the runoff)
1) Indicate sources, removal, and transformation process taking place in regards of the nitrogen cycle
2) Which removal or transformation processes are likely to be the most significant?
To understand the sources, removal, and transformation processes taking place in the nitrogen cycle in a heavily grazed pasture of fescue grass mixed with clover, we need to consider the various components involved.
1) Sources, removal, and transformation processes in the nitrogen cycle:
a) Sources of nitrogen:
- Biological fixation: Clover, being a legume, has a symbiotic relationship with Rhizobium bacteria, which can fix atmospheric nitrogen into a usable form for plants.
- Fertilizer application: Nitrogen-based fertilizers may have been applied to the pasture, providing an additional source of nitrogen.
- Animal waste: Cattle grazing in the pasture produce waste (urine and feces) that contains nitrogen in the form of urea and other organic compounds.
b) Removal or loss of nitrogen:
- Plant uptake: Both the fescue grass and clover plants take up nitrogen from the soil through their roots, using it for growth and development.
- Leaching: If there is excess nitrogen in the soil, it can be leached or washed away by rainwater, carrying the nitrogen down into deeper layers of the soil or potentially contaminating groundwater.
- Denitrification: Under anaerobic conditions (such as waterlogged soil), denitrifying bacteria can convert nitrate (NO3-) into nitrogen gas (N2), which is released into the atmosphere, effectively removing nitrogen from the system.
c) Transformation processes in the nitrogen cycle:
- Nitrification: In aerobic conditions, nitrifying bacteria convert ammonium (NH4+) into nitrate (NO3-), a form that can be easily taken up by plants.
- Mineralization: Decomposers, such as bacteria and fungi, break down organic nitrogen compounds (e.g., dead plants, animal waste) into ammonium, making it available for plants.
- Immobilization: Microorganisms can also take up available nitrogen from the soil to build their own biomass, temporarily reducing the amount of nitrogen available for plant uptake.
2) Most significant removal or transformation processes:
In the given scenario, the most significant removal or transformation processes in the nitrogen cycle are likely to be:
- Plant uptake: Both the fescue grass and clover plants will actively take up nitrogen from the soil, as they require it for growth. This process helps to reduce the nitrogen concentration in the soil.
- Leaching: Due to the absence of recent rainfall and the soil being drained below field capacity, leaching may not be as significant in removing nitrogen from the system. However, if there is excessive nitrogen available in the soil, even a small amount of water runoff (from rain or animal activity) can wash away some nitrogen.
- Denitrification: If the soil becomes waterlogged or has poor drainage, denitrification can occur, converting nitrate into nitrogen gas. However, this process may not be as significant in a heavily grazed pasture unless there are waterlogged areas or standing water present.
In summary, the sources of nitrogen in the heavily grazed pasture include biological fixation, fertilizer application, and animal waste. The removal or loss of nitrogen occurs through plant uptake, leaching, and denitrification. The most significant removal or transformation processes in this scenario are plant uptake and, to a lesser extent, leaching.