Certified Crop Advisor Practice Exam

What is the chemical uptake form of nitrogen?

1. NH4+

2. NO3-

3. NH3

4. N2

The correct answer is: NO3-

The chemical uptake form of nitrogen that is most readily assimilated by plants is nitrate (NO3-). This form of nitrogen is highly soluble in water, making it easily available for plant roots to absorb. Nitrate is a key component of amino acids and nucleic acids, which are essential for plant growth and development. When plants take up nitrate, they often convert it into ammonium (NH4+) through a process called reduction before using it to synthesize necessary organic compounds. This process is vital for plants as they require a steady supply of nitrogen to support various physiological functions including chlorophyll formation and energy transfer. In contrast, while ammonium (NH4+) is also a form of nitrogen that plants can uptake, it is less mobile in the soil solution compared to nitrate and can lead to toxicity at high concentrations. Ammonia (NH3) is primarily a gas at ambient conditions and only minimally contributes to plant uptake, while molecular nitrogen (N2) is inert and unavailable to plants without being converted by nitrogen-fixing microorganisms in the soil. Thus, nitrate's properties as a soluble and easily absorbed ion make it the primary form of nitrogen uptake in plants.