1. Agricultural Yearbook of Tibet, Qinghai, Gansu, Ningxia, Inner Mongolia, Shaanxi, Shanxi, Henan, Shandong, Yunnan, Guizhou, Sichuan, Hubai, Hunan, Jiangxi, Anhui, Jiangsu, Shanghai, Zhejiang, Fujian, Guangdong and Guangxi provinces, municipalities and autonomous regions (1996), China Agricultural Press. Beijing
2. Statistical Yearbook of Tibet, Qinghai, Gansu, Ningxia, Inner Mongolia, Shaanxi, Shanxi, Henan, Shandong, Yunnan, Guizhou, Sichuan, Hubai, Hunan, Jiangxi, Anhui, Jiangsu, Shanghai, Zhejiang, Fujian, Guangdong and Guangxi provinces, municipalities and autonomous regions (1996), China Statistic Publishing House. Beijing
3. Cai GX, Fan XH and Zhu ZL (1998) Gaseous loss of nitrogen from fertilizers applied to wheat on a calcareous soil in North China Plain. Pedosphere 8: 45–32
4. Chen BC, Wen BQ, Tang JY and Liu ZZ (1994) Effect of Azolla on N balance in rice paddy fields. Acta Agriculturae Nucleatae Sinica 8: 97–102
5. China Agricultural Technology and Economy Manual (1983) Agriculture Press, Beijing, pp 105–291