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

Abstract

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 15 N-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 ~47% and ~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 ~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.

Simulation of rice paddy systems in SWAT: A review of previous applications and proposed SWAT+ rice paddy module

“…[21] China Fengyu (219) Rice paddies were located in the lower parts of landscapes; rice comprised 11.8% of the land area; rice grown from May to September; rotated with broad bean or rapeseed; manure and fertilizer application rates reported for three dates; paddies were simulated with the SWAT pothole routine.…”

“…As noted in the Introduction, rice paddies can be sources of sediment [2,20,24,25] , nutrients [15][16][17][18][19][20][218][219][220] , pesticides [7][8][9][10][11][12][13][14] and greenhouse gas (GHG) emissions [17,22] , and also exacerbate other environmental problems [17,22] . However, rice paddies may also provide ecosystem services similar to wetlands during inundation periods, such as supporting ecosystems and biodiversity, groundwater recharge or water purification, and reduced N exports [21,212,213] .…”

“…Fertilizer can be applied prior to paddy flooding, in slow-release forms to rice seedlings growing in nursery boxes (prior to transplanting) or post-transplanting to inundated paddies in either liquid or granular forms. Application of nitrogen to an inundated paddy will dissolve in the ponded water instantly or over time and can ultimately seep into soils via infiltration, be captured in discharge to downstream water bodies, or released atmospherically via denitrification and other processes [218][219][220] . Nitrogen fertilizer applied prior to inundation or via transplanted seedlings can also be lost through those pathways, although those application methods are likely less vulnerable.…”