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PREFACE ABSTRACT CHAPTER 1 Introduction 1.1 Background 1.2 Literature review 1.3 Methodology 1.4 Organization CHAPTER 2 The contribution of seed variety to rice yield increases 2.1 Rice yield changes in China 2.2 Evolution in rice seed varieties in China 2.3 Specification for rice yield model 2.4 Model estimation 2.5 Empirical results 2.6 Summary CHAPTER 3 The contribution of seed variety to wheat yield increases 3.1 Wheat yield changes in China 3.2 Evolution of wheat seed varieties in China 3.3 Specification for the wheat yield model 3.4 Model estimation 3.5 Empirical results 3.6 Summary CHAPTER 4 The contribution of seed variety to corn yield increases 4.1 Corn yield changes in China 4.2 Evolution in corn seed varieties in China 4.3 Specification for the corn yield model 4.4 Model estimation 4.5 Empirical results 4.6 Summary CHAPTER 5 The contribution of seed variety to soybean yield increases 5.1 Soybean yield variation in China 5.2 Evolution in soybean seed varieties in China 5.3 Specification for soybean yield model 5.4 Model estimation 5.5 Empirical results 5.6 Summary CHAPTER 6 The contribution of seed variety to cotton yield increases 6.1 Cotton yield variation in China 6.2 Evolution in cotton seed varieties in China 6.3 Specification for the cotton yield model 6.4 Model estimation 6.5 Empirical results 6.6 Summary CHAPTER 7 The contribution of seed variety to rapeseed yield increases 7.1 Rapeseed yield changes in China 7.2 Evolution in rapeseed seed varieties in China 7.3 Specification for rapeseed yield model 7.4 Model estimation 7.5 Empirical results 7.6 Summary CHAPTER 8 Conclusion and policy recommendations