1. Introduction
The Taihu Lake region (TLR) in the Yangtze River delta (Fig. 1)
covers 36,500 km2. As one of the five major rice production regions
in China, TLR has 75% of its total land growing rice. Rice-wheat
rotation has been practiced here for thousands of years (Li, 1992).
This region is one of the most fertilized regions with nitrogen
(N) in the world. Currently, the annual application rate of synthetic
N fertilizers is as high as 500–600 kg N ha−1 for two crops
(Xing et al., 2002). There is, therefore, growing concern about
environmental impacts induced by the high N loads (Zhu et al.,
2006).