Tracking the Fate of Fertilizer Nitrogen in a Paddy Rice Field Using Isotope Technology.

The aim of this study was to track the fate of nitrogen derived from fertilizer (Ndff) after fertilization. A field in situ experiment covering an entire growing season by using 15N-doubly-labelled urea as fertilizer was conducted at a paddy field inSanjiang Plain in northeastern China. Results showed that approximately 70% of total nitrogen (TN) output load was from Ndff, and the lateral seepage contributed ~47% and ~40% of TN and Ndff output loads, and the rest of the TN and Ndff output loads were derived from runoff and artificial drainage. The Ndff contents in paddy root, stalk, foliage and kernel increased with increasing fertilization dosages -- from the tillering stage to mature stage. Ndff accumulated in the root, stalk and foliage during tillering and the milk stage migrated to the kernel in the mature stage. Most of the residual Ndff in soil was distributed in the top layer (0-10 cm). Crop utilization and gaseous loss were the main fates of Ndff in the paddy field. The proportion of crop utilization with an average value of ---37% increased from 30.29% to 43.52% with increasing fertilization dosages, while the proportion of gaseous loss decreased from 49.61% to 32.74% with increasing fertilization dosages. 180 kg N hm-2 was the optimum fertilization dosage for crop utilization rate and non-point source pollution control in the rice-growing area of Sanjiang Plain. [ABSTRACT FROM AUTHOR]