What type of nitrogen is primarily taken up by plants?

Plants primarily take up nitrogen in the form of ammonium (( NH_4^+ )) and nitrate (( NO_3^- )). This is because these forms are readily available and can be directly absorbed by plant roots. The conversion of elemental nitrogen from the atmosphere into a usable form for plants is a complex process that relies on nitrogen-fixing bacteria, which is why plants cannot directly utilize elemental nitrogen.

While urea nitrogen is another source of nitrogen that can be taken up by plants, it must first be converted to ammonium in the soil before it can be absorbed, making it a less direct source compared to ammonium and nitrate. Nitrous nitrogen refers to compounds like nitrous oxide, which are not utilized by plants as a nutrient source. Thus, the reliance of plants on ammonium and nitrate encompasses the most efficient and straightforward mechanisms for nitrogen uptake in their growth and development.