Movement and Retention of NH4-N in Wetland Rice Soils as Affected by Urea Application Methods

This document presents a study on the movement and retention of ammonium nitrogen (NH4-N) in wetland rice soils, focusing on the impact of different urea application methods. The research was conducted by Imran Ahammad Siddique and his colleagues from the Department of Soil Science at Bangladesh Agricultural University and the International Fertilizer Development Center. The significance of the study lies in the fact that rice is a major crop in Bangladesh, and understanding the behavior of NH4-N in the soil is crucial for optimizing fertilizer application and increasing nitrogen use efficiency. The study investigated the effects of urea deep placement (UDP) and broadcast application methods on NH4-N movement and retention in wetland rice soils. UDP involves placing urea deep into the soil, concentrating NH4-N in the anaerobic layer, and reducing its movement to the soil surface or floodwater. The results showed that deep placement of urea increased NH4-N retention in the soil for a longer period compared to broadcast methods, potentially reducing the need for multiple split applications. Additionally, it was found that UDP could improve nitrogen use efficiency and increase rice production. The characteristics of submerged soil were also examined, including the depletion of oxygen, reduction of certain ions, limited gas exchange, and changes in soil pH. Understanding the nitrogen transformation processes in flooded soils is essential due to the solubility and potential toxicity of inorganic nitrogen. The study aimed to investigate the movement and retention of NH4-N during the rice-growing season using different application methods and nitrogen rates. Pore water samples were collected from UDP and broadcast plots at various depths and time points. The results demonstrated that NH4-N concentration decreased gradually over time, and its horizontal movement was significant up to 10 cm from the placement point. The diffusion area near the rice root zone showed the highest NH4-N concentration, while UDP retained higher NH4-N levels in the soil than broadcast urea.
Deep placement, Nitrogen-use efficiency, Rice