Preferable form of nitrogen for rice under submerged soil conditions is ____________?

A. NH4
B. NO3
C. NO2
D. All of these

In submerged (flooded) soil conditions, which are typical for rice paddies, the oxygen levels are low, leading to anaerobic conditions. Under these conditions, ammonium (NH4+) is more stable and available for plant uptake compared to nitrate (NO3-) and nitrite (NO2-), which are less stable and can be lost through denitrification processes. Rice plants are well-adapted to take up nitrogen in the form of ammonium, making NH4 the preferable form of nitrogen in submerged soils.