The raw value of the normal yield of rice is estimated by a multiple regression of the actual yield on the year effect and damage rate. The final normal yield is determined from the raw value taking in opinions of experts concerned. However, there are several theoretical problems in the present estimation procedure. We propose that the estimation of the normal yield should be based on the base yield defined as the sum of the actual yield and the amount of damage. The base yield is the yield that could be obtained if there were no damage. It is expected to vary smoothly. However, it does not always so in the actual data. We set up the hypothesis H₁ that the trend of base yield changes at some year in accordance with some qualitative change in the cultivation method, varieties, and so on, and the hypothesis H₁' that there exists the systematic error in estimating of the degree of damage against the null hypothesis H₀ that the trend varies smoothly. We applied a fuzzy model with fuzzy rules taking the form that if ~ then ~. The best fitted hypothesis (number of rules) to data was assessed by AIC. This procedure was applied to the yearly data from 1970 to 1989 in all Japan, Hokkaido and Kouchi Pref. The hypothesis H₁' with two fuzzy rules was adopted in the case of all Japan and Hokkaido. The different trend of the base yield was apparent between the cases where the degree of damage was `small' and `large'. On the other hand, H₁ with two non-fuzzy rules was adopted in the case of Kouchi Pref. It was shown that the trend of the base yield may change at 1976. When H₁ is adopted, we propose that the estimation of the normal yield is obtained by subtracting normal values of the amount of damage under respective rules from the trend of the base yield. On the other hand, when H₁' is adopted, we assume that there exists the systematic error in estimating of the degree of damage in the case where the degree of damage is `large'. We propose that the estimation of the normal yield is obtained by subtracting the normal value of the amount of damage revised on the systematic error from the trend of the base yield revised on the systematic error.

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As livestock production in Japan becomes more intensive, livestock wastes cause serious environmental problems. To obtain a fundamental data for solving these problems, nitrogen flows in dairy farms are estimated quantitatively. The nitrogen flow system in dairy farms consists of ten parts; chemical fertilizer, self-supplying feed, purchased feed, milk, sold cattle, beddings, wastes and manure (sold, used for their own croplands and unknown). The estimated amounts of nitrogen in cattle wastes are 3,731kg/farm/year at 1985, 4,965kg/farm/year in 1990 in Hokkaido, and 1,947kg/farm/year in 1985, 2,445kg/farm/year in 1990 in the areas except Hokkaido. In Hokkaido, about 203kg/ha/year (1985: 205kg/ha/year, 1990: 201kg/ha/year) nitrogen in cattle wastes were used for their own croplands. In the areas except Hokkaido, about 513kg/ha/year (1985: 501kg/ha/year, 1990: 525kg/ha/year) nitrogen were used for their own croplands. The differences between loadings of nitrogen onto croplands and removed nitrogen by forage crops were about +102kg/ha/year (1985: +103kg/ha/year, 1990: +100kg/ha/year) in Hokkaido, and about +335kg/ha/year (1985: +316kg/ha/year, 1990: +354kg/ha/year) in the areas except Hokkaido.

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We investigated the capacity of food production in China. The arable land has been approximately constant since 1960 and is about 1x10⁸ ha in China, though the population has increased from 0.65 to 1.2 billion. The arable land per person was 0.08 ha in 1992. This is relatively small as compared with that in the western countries. The area of pasture is 4x10⁸ ha. A small amount of meat produced in the pasture. The fish catch has increased and was 1.31x10⁷ ton year^-1 in 1992. Though the fish catch becomes the top of the world, the fish meat consumption rate per person is still 1/10 as compared with that in Japan. The cereal production per unit arable land is 4.3 ton ha^-1 year^-1. It seems almost saturated. The large amount of chemical fertilizer input to the field is responsible for the shallow underground water pollution by nitrate. There is little room for the increase of the agricultural production in China. China must import cereals to produce meat, when China will be a developed country.

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