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 (N-dff) after fertilization. A field in situ experiment covering an entire growing season by using N-15-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 N-dff, and the lateral seepage contributed similar to 47% and similar to 40% of TN and N-dff output loads, and the rest of the TN and N-dff output loads were derived from runoff and artificial drainage. The N-dff contents in paddy root, stalk, foliage and kernel increased with increasing fertilization dosages - from the tillering stage to mature stage. N-dff 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 N-dff in soil was distributed in the top layer (0-10 cm). Crop utilization and gaseous loss were the main fates of N-dff in the paddy field. The proportion of crop utilization with an average value of similar to 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.