This is the fourth report on the history of the reclamation of the Red River Delta. It discusses the first establishment of an embankmental system in the West Flood Plain in the Tran Dynasty.
 As discussed in the previous papers, no evidence has been found for a large-scale embankmental system along the Red River and other big rivers before the 13 century, although there were small village-scale embankments in the Old Delta area. However, according to the geographical descriptions of the early Nguyen Dynasty, a close-polder type embankmental system already existed in the West Floodplain in the Le Period (1428-1789). Documents on the floods and village settlements patterns in the early Le Period (the latter part of the 15th century) indicate that the first establishment of the embankment predates this period, probably occurring in the Tran Dynasty.
 The Dai Viet Su Ky Toan Thu states that the Tran government constructed a large-scale embankment along the Red River from the upper stream to the river mouth called Dinh Nhi in 1248. A record of agricultural damage in the Tran Dynasty shows that flood damage increased from around 1250,and that after the construction of 1248,the area of tenth-month rice in the floodplain expanded rapidly. Furthermore, an analysis of the place names of An Nam Chi Nguyen suggests the presence of a big horse-shoe polder surrounding the West Floodplain. This was, probably established by virture of the embankment constructed in 1248. After this period, the Red River Delta was reclaimed by engineering methods under state control and not by agronomic methods

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The focus of this paper is on the worksharing in Philippine rice-farming communities. In these villages, farmers depend on hired labor provided by landless, other farmers and their families. This implies that farmers share agrarian work with each other, especially in transplanting and harvesting. I define mutual employment as work-sharing by farmers and their families under hired labor contracts. Such contracts are accompanied by incomesharing, because payment includes a share of the harvested yield, normally one sixth to one eighth.
 Why do farmers hire each other? One explanation is the uncertainty of yields arising from disparities in the condition of fields. For example, lowland is prone to flooding, while upland is prone to drought. Mutual employment implies that the farmers harvest from both type of field and the low of large numbers clearly applies in this case. So, the farmers hired each other share risk and reduce variance of the gross income compared with that of yield. And the farmers don't have a problem of the moral hazard since they monitor each other in transplanting and harvesting. Risksharing and incentive are compatible in mutual employment system.

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The micromorphology of peats was studied in order to characterize the various stages of decomposition and to describe the overall change of organic matter after deposition. The fallen plant materials consist of leaves, wood blocks, branches and twigs, and they are categorized as litter. Several microfabrics, including fibric, hemic and sapric materials, occur in the course of decomposition. Fibric material is characterized by tissues of recognizable botanical origin, while the hemic and sapric materials are characterized by mainly unrecognizable tissues.
 Peats covered by dense forest are mostly characterized by fibric peat in the bottom layer, which is mainly derived from ferns and grasses. In the upper layers these peats are commonly hemic or sapric peats containing many wood blocks derived from the former vegetation. In cultivated areas, thin peat layers are categorized as sapric peats.
 The macro- and microorganisms attacking the plant debris control the process of micromorphological change of organic matter and hasten the decomposition of fallen-plant materials. However, the degree of decomposition of peats is closely related to the water contents of organic materials.

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