Controlled Irrigation and Drainage Reduce Rainfall Runoff and Nitrogen Loss in Paddy Fields.

Yanmei Yu,Junzeng Xu,Yujiang Xiong,Pingcang Zhang,Yan Meng

doi:10.3390/ijerph18073348

Abstract

In southern China, the growing period of rice is synchronized with the rainy period, and the loss of nutrients (such as nitrogen) due to unreasonable irrigation and drainage, along with rainfall and runoff, has become the main source of agricultural nonpoint source pollution. The laws of runoff and nitrogen loss in paddy fields under different irrigation and drainage modes are not clear. In this study, field experiments were adopted to observe the runoff and nitrogen loss under typical rainfall and throughout the whole growth period. The results showed that, compared with the traditional irrigation and drainage mode, the controlled irrigation and drainage mode reduced the drainage of two typical rainfall processes by 47.5% and 31.3% and the peak drainage by 38.9% and 14.4%. Compared with those under the traditional irrigation and drainage mode, the average concentrations of total nitrogen, nitrate nitrogen, and ammonium nitrogen under the controlled irrigation and drainage mode were reduced by 22.2%, 22.7%, and 27.8%, respectively, during the whole rainfall process on July 21 and were decreased by 27.1%, 11.4%, and 25.6%, respectively, on August 25. In irrigated rice areas, under the controlled irrigation and drainage mode, drainage was reduced after two intercepts through paddy fields and drainage ditches. The nitrogen concentration in the drainage ditch decreased due to the increase in retention time and the effect of the ditch and field wetland. Compared with the traditional irrigation and drainage mode, the total nitrogen, nitrate nitrogen, and ammonium nitrogen loads of the controlled irrigation and drainage mode were reduced by 69.8%, 65.3%, and 69.7%, respectively.

Highlights

Rice is the most important grain crop in China, accounting for 29% of the world’s output and 19% of the world’s planted area [1]
Under the Controlledirrigation irrigation and and drainage drainage (CID) mode, runoff in the drainage ditches started at 4 h and 2 h after rainfall in the two typical rainfall processes, and the drainage was 7.1 mm and 7.8 mm, respectively, 47.5% and 31.3% lower than the TID mode
The soil of the paddy fields under the CID mode was in the unsaturated state for a long time, and the time of alternating wet and dry states between paddy fields and drainage ditches was reduced, which greatly reduced the vertical and lateral leakage and drainage of the paddy fields [6]

Summary

Introduction

Rice is the most important grain crop in China, accounting for 29% of the world’s output and 19% of the world’s planted area [1]. Under the increasingly acute contradiction of water resource supply and demand, implementing water-saving irrigation, and using existing water resources efficiently to promote the virtuous circle of society and economy are important tasks, and inevitable choices for the rational development and utilization of agricultural water resources. In recent years, the loss of nitrogen and other nutrients caused by excessive fertilization in paddy fields to maintain rice yield and stable development has become the main source of agricultural nonpoint source pollution in southern China [3,4,5,6,7]. In the early stage of the rainy season, the increase in suspended matter in surface water causes the loss of nitrogen in runoff due to the hydraulic

Results

Discussion

Conclusion