Consider a corn field in the spring at the end of April. The field has been heavily tilled in the fall and all residues have been incorporated in the soil, and are decomposed by this time. Chemical fertilizer (an inorganic fertilizer with only nitrate nitrogen - NO3) has been applied under suitable (not too wet) conditions a few days ago and the farmer has successfully planted corn before rain occurred. Now it is raining heavily and temperatures are mild at 20 degrees C.
1) What parts of the nitrogen cycle are taking place in the field? Indicate the sources as well as removal and transformation processes.
2) What removal or transformation processes are likely to see the most activity?
3) What parts of the cycle would be involved if urea fertilizer [CO(NH2)2] was applied instead of the nitrate fertilizer? (Indicated sources, removal and transformation processes, and which processes would see the most activity)
1) In this cornfield, several parts of the nitrogen cycle are taking place. Firstly, the source of nitrogen is the chemical fertilizer that was applied to the soil, which consists only of nitrate nitrogen (NO3). The nitrate nitrogen undergoes several processes in the field. One key process is nitrification, where bacteria convert ammonium (NH4+) to nitrite (NO2-) and then further to nitrate (NO3-). Another process is denitrification, where certain bacteria convert nitrate (NO3-) back into nitrogen gas (N2), which is released into the atmosphere. Additionally, there may be some nitrogen fixation taking place, where certain bacteria convert atmospheric nitrogen gas (N2) into ammonia (NH3) that can be used by plants.
2) The removal or transformation processes that are likely to see the most activity in this situation are nitrification and denitrification. Nitrification converts ammonium (NH4+) to nitrate (NO3-), which is the form of nitrogen that plants use. The heavy rain and mild temperatures provide favorable conditions for nitrifying bacteria to thrive, leading to significant nitrification activity. Denitrification, on the other hand, converts nitrate (NO3-) back into nitrogen gas (N2), which can result in nitrogen loss from the system. The heavy rain can create waterlogged conditions in the soil, further promoting denitrification.
3) If urea fertilizer (CO(NH2)2) was applied instead of nitrate fertilizer, different parts of the nitrogen cycle would be involved. Urea is a form of organic nitrogen that needs to be transformed into a usable form for plants, such as ammonium (NH4+) or nitrate (NO3-). Therefore, the first major process involved would be hydrolysis, where urease enzymes break down urea into ammonium (NH4+). Once ammonium is formed, it can undergo the same nitrification and denitrification processes mentioned earlier, ultimately being transformed into nitrate (NO3-) or released as nitrogen gas (N2). However, it's important to note that with urea fertilizer, there is an additional risk of ammonia volatilization, where ammonium can convert to ammonia gas and be lost to the atmosphere. The activity of urease enzymes and the loss of ammonia gas would be the processes most affected in this scenario.