The important contribution to agricultural science by A.D. Thaer and J.H.v. Thünen is not a question that needs to be argued. This paper aims not only to survey the historical studies of these classics using quite new information after the reunion of the two Germanies, but also to discuss the current interpretations in view of sustainable agriculture by these classical models as a blueprint of the future. The author could find some aspects of analytical tools from these models to construct a methodology of agroecology, that is to say, an optimization of ecology and economy in agriculture. It would be also possible to develop the theory of agroecology on the basis of these classical studies.

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This paper measures the gross stock of capital of cultivators and tractors in Japanese agriculture during the period from 1975 to 2000, with special focus on the quality changes. The physical stock value method is applied, taking the quality difference of the stock produced in various years into account. First, the physical stock is broken down by the year produced. Second, the quality adjustment index is calculated for each year. Third, the quality-adjusted physical stock is calculated by using the broken-down physical stock and the quality adjustment index. Last, the gross stock of capital is calculated as the product of the price and the quality-adjusted physical stock.
This paper also estimates the gross capital formation and the durable period. Conventional gross capital stock and gross capital formation, which leave quality changes out of consideration, are also measured.
The results of measurement show that the gross capital stock of cultivators and tractors in Japanese agriculture with quality changes has grown more rapidly than that of conventional estimation.

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If agricultural drainage from an area imposes costs on society through damaging the environment, and if the measurement of the drainage discharged from each plot in the area is too costly, then it may be necessary to control the drainage by regulating the irrigation tariffs levied on agricultural producers operating there. The purpose of this paper is to analyze how, in such a situation, the regulator of the irrigation tariffs can control drainage and enhance social welfare by using increasing block tariffs for irrigation water.
This paper first explains irrigation technology choices by producers and the social costs of their water application when a linear tariff or two-tier increasing block tariff is used to charge for irrigation water. It then examines how variations in the tail block rate of the increasing block tariff affect social welfare, changing agricultural production decisions.
When a two-tier increasing block tariff is used to price irrigation water, there can be land areas where producers apply larger volumes of water using traditional irrigation technology. In such a case, it is possible that rises in the tail block rate of the increasing block tariff induce the producers in the area i) to employ modern irrigation technology instead of traditional irrigation technology, or ii) to reduce water application while continuing to use traditional irrigation technology. This paper clarifies what conditions are sufficient for these effects of rises in the tail block rate to contribute to the enhancement of social welfare. The paper also deduces sufficient conditions for the existence of an increasing block tariff for irrigation water that yields a level of social welfare higher than a given linear irrigation tariff. A numerical simulation is conducted to illustrate how two-tier increasing block tariffs can raise social welfare with the above effects.

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