With a drastic economic growth, substantial income increase and rapid urbanization over the last three decades, China's grain market has undergone a sustainable increase in the demand, particularly for feed grains driven by the growing demand for livestock products. These dietary changes, together with population growth, are projected to keep driving China's future grain demand. On the other hand, a decrease in arable land and lack of water resources, etc., contribute to the stress on the grain supply. Such challenges from both the demand and the supply sides of grain market give rise to concerns about China's grain security. Moreover, as the world's most populous country with 1.34 billion people, China plays a crucial role in the global supply-demand balance since it accounts for about 20% of global grain production and consumption. If China cannot maintain its grain basic self-sufficiency, the problem of "Who will feed China" (Brown, 1995) shall be not only an issue for the country but also a formidable question influencing the global grain security.

This thesis seeks to provide an analysis, from both the demand and supply sides, of whether China can achieve the sustainable self-sufficiency in grains―particularly for feed grains―in the near future. However, the aim of this research is not to project directly how much China's grain self-sufficiency rate will be in the future; instead, it aims to investigate the self-sufficiency problem by simulating possible impacts of China's increasing grain demand on the world price.

Chapter 1 gives backgrounds for this study from both theoretical and practical perspectives. Despite several important drawbacks in his analysis, Lester Brown's book has evoked widespread and intense discussions. His pessimistic projections, though seldom scientific, stimulate economists and even the Chinese government itself to reconsider the grain problems in China. Enormous projections on China's grain demand come out with a variety of results due to their varied assumptions, data sources and model structures. Reflected in China's grain policy, the Chinese government set their declared grain self-sufficiency goal at 95% in the two long-term plans in 1996 and 2008. According to official statistics, domestic grain production met 98% of grain consumption up to 2007, and the self-sufficiency rate of cereals as a whole amounted to 106%; in other words, a high degree of self-sufficiency was achieved.

In spite of this, China's grain problems are still faced with challenges and pressures. Although directly consumed food grains account for more than 50% of China's total grain demand, the proportion has been continually declining since the mid-1980s. In contrast, demand for feed grains has been growing to more than 30% of the overall grain demand in the 2000s and is projected to keep increasing due to the burgeoning livestock demand in the years ahead. China's grain self-sufficiency problem, in this sense, is essentially a problem of feed grains. Therefore, demand for livestock products need to be researched in detail in order to analyze the feed grain issue. This, in combination with an analysis of the supply side, shall contribute to the design of a supply-demand model of grains that can estimate the level of influence China has on global grain security. Previous studies in this field are reviewed, and methods, objectives and originalities in this study are clarified. The framework of this thesis is also introduced.

Chapter 2 provides an overall analysis on the changing direction of China's dietary pattern. By making principal component analysis (PCA) on food consumption data from 174 countries, it finds that China has been progressing for advanced diets by consuming less staple food and more meat, aquatic and dairy products for proteins. However, results of the PCA also show that China is not following the Western pattern of diet highly dependent on meats and dairy products such as the US and UK, but is moving towards the dietary pattern of East Asia's developed countries (regions) by consuming more fish and seafood like Japan, South Korea, Taiwan and Hong Kong; This finding is important because it poses the possibility of much less meat consumption contrary to some economists' assumptions.

In chapter 3, characteristics of China's food consumption are investigated in both urban and rural areas based on estimations of expenditure elasticities. As is well known, urban-rural gaps are significant in China. Clear distinctions exist between urban and rural diets owing to differences in income levels, developmental stages, and lifestyles. It is essential to incorporate both urban and rural China into the analyses in order to have a complete and precise understanding of China's feed grain demand. In this chapter, the expenditure elasticities in both urban and rural areas are estimated through two methods, namely the double logarithmic function (DLF) analysis and the LA/AIDS (linear approximate almost ideal demand system) analysis.

Many results are common across the DLF and the LA/AIDS analyses. First, expenditure elasticities of most food items tend to decline in both urban and rural areas as the income increases. Second, the urban-rural gaps exist in food consumption, likely due to differences in the speed of economic growth and income level. On the whole, the expenditure elasticity is higher in rural China than in urban China for the same item. Third, similar dietary patterns and preferences are found between urban and rural areas. Estimations show that the Chinese people tend to consume more aquatic products than meats and poultry when their income increases; this pattern is different from the Western experience. Among meats and poultry, poultry is much more income elastic than pork, beef, or mutton. Moreover, among the livestock products, although the expenditure elasticities of beef and mutton are higher than that of pork, the expenditure share of pork is significantly larger than those of beef and mutton.

These results can be explained by China's dietary characteristics. Despite the influences China has felt from the Western diets over the last three decades that have led to higher consumption of milk and beef, the Chinese still regard aquatic products as premium foods, believe in the nutrient value of poultry, and retain pork as their predominant meat product. Compared with beef, the provision of aquatic products, poultry, and pork requires far fewer feed grains; this means that the increase in feed grains may be mild and thus leads to less stress on China's feed grain balance than the OECD projected.

Chapter 4 seeks to develop a supply-demand model of feed grains. To determine the demographic assumptions in the model related to population changes, previous studies in this field, including analyses of historical changes and projections for the future changes, are reviewed in detail.

Then in order to decide the assumptions concerning China's domestic supply capacity in the supply-demand model, detailed reviews of previous studies in this field are performed. In addition, original estimations are carried out in which area of arable land and yield are both taken into consideration.

Finally, a supply-demand model is built in chapter 4. Three scenarios are developed by assuming different expenditure elasticities for beef and pork consumption: the expenditure elasticities for urban and rural China estimated in chapter 3, and another the OECD estimated and uses to make projections of China's grain demand in the AGLINK-COSIMO model. The simulation results show significantly different projections among these three scenarios. Compared with the scenario using the OECD expenditure elasticities, projections with the estimated expenditure elasticities for both urban and rural China in the present study yield a less rapid increase in China's feed grain demand and thus price of grains. According to this analysis, China is expected to sustain its demand for grains without jeopardizing world grain's supply-demand balance and leading to a global price boom. In conclusion, policy proposals are made in order to assist sustainable grain self-sufficiency in China.

Finally in chapter 5, conclusions of the whole thesis are summarized as follows:

First, China is not following and will not follow the Western dietary pattern as income increases. In the overall changing direction, it is found that rather than consuming large quantities of beef and dairy products for protein as some economists have envisaged, China is moving towards the pattern of East Asia's developed countries (regions) with preferences for aquatic products. Moreover, from analyses of expenditure elasticities, the Chinese people, in both urban and rural areas, are projected to spend their increased income on fish and seafood rather than poultry, beef or pork.

Second, the future increase in China's grain demand is expected to be manageable without breaking the world's grain supply-demand balance and leading to a price boom. In this sense, China is predicted to be able to achieve a sustainable self-sufficiency in grains in the near future. However, attention should be paid to several assumptions based on which these conclusions are reached, such as population growth at a medium rate, constant yield, and static economic growth predictions.

本研究の目的は、中国における穀物自給の持続可能性を分析することである。

過去30年間にわたる経済成長に伴い、中国では人々の食生活が穀物などのデンプン質中心のものから水産物、肉類、乳製品を多く消費するタンパク質中心のものに変わりつつある。そのため、一人当たりの食用穀物消費は安定的に推移している反面、タンパク質を生産するのに必要な飼料穀物の需要は増加している。一方、耕地面積の減少や水資源の欠乏などが穀物の供給増加にとって大きな制約となっている。13.5億の人口を抱える中国の穀物需給は自国のみならず、世界全体にとっても大きな課題である。

本研究は研究背景などを述べる第1章と結論を総括する第5章を除けば、食生活パターンの変化と食料消費の特徴を分析する第2章と第3章、それと穀物需給モデルを構築して今後の持続可能性について予測する第4章から構成されている。

まず第1章、序論では研究背景を説明し先行研究を整理した上、論文の構成と本研究の独自性に関して論述した。

第2章では各国(地域)の品目別消費量のデータを用いて主成分分析を行い、新たに2000年以降における中国全体の食生活パターンの変遷を究明した。それによって、70年代以来中国において食生活の高度化が進む中、その方向は欧米のような肉類中心ではなく、同じ東アジアに位置する日本、韓国、台湾、香港と類似する水産物への相対的な嗜好が高い傾向が2000年以降でも継続していることがわかった。このような趨勢が今後も続けば、将来の中国での肉類消費による飼料穀物の需要増加は緩やかなものになる可能性を示唆した。

第3章では需要の支出弾力性の分析を通じて都市部と農村部における食料消費のそれぞれの特徴を明らかにした。

将来の中国における飼料穀物の需要の全貌をより詳細に捉えるため、都市部と農村部の双方を対象に、それぞれ地域別の食料品目、特に肉類(牛、豚、羊肉)、水産物、家禽の需要の支出弾力性を推計した。推計は両対数関数(DLF)と需要システム(LA/AIDS)の二つの方法を用いて行ったが、その結果には高い整合性が見られた。

推計結果を基に都市部と農村部の食料消費の特徴を比較したところ、大多数の品目において支出弾力性が所得の増加に伴い下がっていく傾向、水産物と家禽の弾力性が肉類(牛、豚、羊肉)より高いことなどの共通点が見られた一方、支出弾力性には大きな差異が存在することが分かった。これは、主に所得の格差や生活習慣に起因すると考えられる。

中国の食料消費構造には欧米からの影響だけでは説明できない独特の特質も存在することが明らかになった。所得の1%の伸びに対する水産物消費の伸びは、家禽と肉類の伸びよりも大きく、また家禽と肉類を比較した場合では、家禽の方が大きく伸びていることが分かった。さらに、肉類の中でも牛肉と羊肉の支出弾力性が豚肉のそれより高いことが示された。このような結果は中国の食生活における特質、すなわち海鮮物へのプレミアムグッズ意識、家禽に対する高栄養価値イメージ、豚肉中心の肉消費構造などから解釈できる。

第4章では飼料用穀物需給モデルを構築するため、まず前半で需要サイドを規定するもう一つの重要要素である人口要因の歴史的変遷と将来予測を詳説し、穀物供給を左右する耕地面積と単収の状況も分析した。さらに後半ではこれらの分析結果をベースに、第3章の両対数関数分析で得られた需要の支出弾力性を用いて、飼料用トウモロコシの需給モデルを構築した。そして本研究から推計された都市部と農村部での需要の支出弾力性と、OECDが中国の食料需要を予測した際に使われる高い支出弾力性を用いた三つのシナリオでシミュレーションした結果、OECDのシナリオと比較して本研究が示した中国の肉類(豚肉と牛肉)消費量増加が緩やかなものであることがわかった。同時に将来の中国の飼料用トウモロコシ需要が世界のトウモロコシ需要に占める割合がOECDのシナリオに示されるような上昇傾向ではなく、安定または低下する可能性が示唆された。

最後に、第5章では結論として二つのことをまとめた。一つはこれまでの中国の食生活パターンの変化は単純な欧米の後追い的な変化ではなく、今後も単純に欧米化する可能性が低いことである。もう一つは中国が世界の食料需給バランスを崩すことなく、およそ将来20年間にわたり穀物自給を持続的に保つことができる可能性である。

以上のように、本研究は今後さらに世界の食料需給においてプレゼンスを高める中国おける穀物自給の持続可能性を需給モデルで明らかにした優れた研究である。特に需要の支出弾力性の分析については、都市部のみならず従来なかなか入手困難とみられていた農村部の最新データの収集にも成功し、需要システム・モデルを構築した。また、都市部と農村部で推計された需要の支出弾力性を用いた飼料用トウモロコシ需給モデルを通じ、食料消費の地域格差が穀物需給にどういう影響を与えるかを解明すると同時に、中国が持続的な穀物自給を維持できる可能性を示し、国際機関等による従来の中国の穀物需給分析が過大推定であった可能性を明らかにした意義は大きい。このように、本研究は学術上かつ応用上の価値が高く、よって審査委員一同は本論文が博士(農学)の学位を授与するにふさわしいと判断した。