The high yield of irrigated rice in Yunnan, China ‘A cross-location analysis’ Keisuke Katsura a, * , Shuhei Maeda b , Iskandar Lubis c , Takeshi Horie d , Weixing Cao e , Tatsuhiko Shiraiwa b a Experimental Farm, Graduate School of Agriculture, Kyoto University, Takatsuki, Osaka 569-0096, Japan b Laboratory of Crop Science, Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan c Laboratory of Crop Production, Faculty of Agriculture, Bogor Agricultural University, Darmaga, Bogor 16680, Indonesia d National Agriculture and Food Research Organization, Tsukuba, Ibaraki 305-8517, Japan e Key Laboratory of Crop Growth Regulation of Ministry of Agriculture, Hi-Tech Key Lab of Information Agriculture of Jiangsu Province, Nanjing Agricultural University, Nanjing 210095, China Received 18 September 2007; received in revised form 4 December 2007; accepted 12 December 2007 Abstract A number of field trials on rice productivity have demonstrated very high yield, but reported limited information on environmental factors. The objective of this study was to reveal the environmental factors associated with high rice productivity in the subtropical environment of Yunnan, China. We conducted cross-locational field experiments using widely different rice varieties in Yunnan and in temperate environments of Kyoto, Japan in 2002 and 2003. The average daily radiation throughout the growing season was greater at Yunnan (17.1 MJ m 2 day 1 average over 2 years) relative to Kyoto (13.2 MJ m 2 day 1 ). The average daily temperature throughout the growing season was 24.7 8C at Yunnan, and 23.8 8C at Kyoto. The highest yield (16.5 tonnes ha 1 ) was achieved by the F1 variety Liangyoupeijiu at Yunnan in 2003, and average yield of all varieties was 33% and 39% higher at Yunnan relative to Kyoto in 2002 and 2003, respectively. There was a close correlation between grain yield and aboveground biomass at maturity, while there was little variation in the harvest index among environments. Large biomass accumulation was mainly caused by intense incident radiation at Yunnan, as there was little difference in crop radiation use efficiency (RUE) between locations. Large leaf area index (LAI) was also suggested to be an important factor. Average nitrogen (N) accumulation over 2 years was 49% higher at Yunnan than at Kyoto, and also contributed to the large biomass accumulation at Yunnan. The treatments of varied N application for Takanari revealed that the ratio of N accumulated at maturity to the amount of fertilized N was significantly higher at Yunnan than at Kyoto, even though there was no great difference in soil fertility. The Takanari plot with high N application showed a N saturation in plant growth at Kyoto, which might be related to low radiation and relatively high temperatures during the mid- growth stage. These results indicate that the high potential yield of irrigated rice in Yunnan is achieved mainly by intense incident solar radiation, which caused the large biomass and the N accumulation. The low nighttime temperature during the mid-growth stage was also suggested to be an important factor for large biomass accumulation and high grain yield at Yunnan. # 2007 Elsevier B.V. All rights reserved. Keywords: Rice (Oryza sativa); Radiation use efficiency (RUE); Yield; Yunnan; Nitrogen; Leaf area index (LAI); Temperature 1. Introduction Due to rising population numbers, Asian irrigated rice production must increase by 43% over the next 30 years (Cassman, 1999). However, further expansion of rice planted area is difficult, because most arable land is already used for rice production or converted into urban infrastructure (Horie et al., 2005). Many farmers are now obtaining yields close to those produced at experimental stations (Conway and Toenniessen, 1999), and yield potential of modern rice varieties in irrigated rice fields has stagnated around 10 tonnes ha 1 since the first semidwarf tropical indica variety, IR8, was released in 1966 (Peng et al., 1999). To break this yield barrier, it is very important to clarify the environmental effects on rice productivity, as well as the physiological traits causing high productivity. A number of field observations of grain yields over 13 tonnes ha 1 has been reported, for example in Yunnan, www.elsevier.com/locate/fcr Available online at www.sciencedirect.com Field Crops Research 107 (2008) 1–11 * Corresponding author. Tel.: +81 72 685 0134; fax: +81 72 683 1532. E-mail address: kkatsura@kais.kyoto-u.ac.jp (K. Katsura). 0378-4290/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.fcr.2007.12.007