The coincidence of high temperature and different levels of irradiance is a common feature of tropical and subtropical regions. The objectives of the present study were to examine the effects of high temperature stress under different levels of irradiance on (1) photosynthetic rate and gas exchange characteristics and (2) chlorophyll fluorescence characteristics in mango (Mangifera indicaL. cv. Irwin) . Three-year-old grafted mango trees grown in a plastic house were treated in three growth chambers maintained under three different combinations of day/night temperature and light irradiance; day/night 30/25°C + 600 μmol⋅m^-2⋅s^-1 (T1), 40/25°C + 600 μmol⋅m^-2⋅s^-1 (T2) and 40/25°C + 200 μmol⋅m^-2⋅s^-1 (T3) . The CO₂exchange characteristics indicated that the changes in the temperature regime from 30/25°C to 40/25°C affected the net photosynthetic rate, stomatal conductance, transpiration rate and intercellular carbon dioxide concentration. On the other hand, the changes in light irradiation did not affect these gas exchange characteristics though the net photosynthetic rate decreased under lower radiation level significantly compared to that under higher irradiation level for 52 and 92 hours of treatment. The efficiency of PSII (F'v/F'm) and variable fluorescence (F'v) during the steady state was significantly different among the three treatments. The increase in temperature to 40/25°C at 600 μmol⋅m^-2⋅s^-1 (T2) resulted in a significant decrease in the F'v and F'v/F'm ratio compared to T1. But when the light irradiance was reduced to 200 μmol⋅m^-2⋅s^-1at 40/25°C (T3), the F'v and F'v/F'm ratio increased significantly compared to the values in the plants grown under T1. These results suggested that the changes in irradiance affected the F'v and F'v/F'm ratio more than the changes in temperature. The initial fluorescence (F'o) were opposite to those of F'v under the three treatments. The electron transport decreased abruptly when the irradiance level decreased from 600 μmol⋅m^-2⋅s^-1to 200 μmol⋅m^-2⋅s^-1even when the temperature increased to 40/25°C. However, when the temperature increased from 30/25°C to 40/25°C, without changes in the irradiance level, the electron transport first increased marginally and then decreased abruptly. Our results indicate that stomatal factors are sensitive to changes in the temperature while the non-stomatal factors to changes in the irradiance.

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This paper focuses on agrarian changes of the Bemba living in northern Zambia and their coping strategies for subsistence under rapid economic and political changes. In the research area the villagers made their living in 1983 mainly by the shifting cultivation system called Citemene, but they started semi-permanent cultivation of F₁hybrid maize with chemical fertilizers in 1985. After the mid-1980's, the socio-economic conditions were favorable for maize farming and they continued to practice both the Citemene system for subsistence and maize cultivation for cash economy.
In 1990's they started consuming maize for staple food as well as Citemene crops; finger millet and cassava. This change was related to two factors; (1) Agricultural markets were gradually liberalized and maize sale was not particularly attractive to the farmers and (2) suitable woodland for Citemene system became limited by the resettlement project of the Government; hence land restriction caused shortage of traditional staple food.
Though they started to consume maize as staple food, the food conditions became insecure because of the unstable agricultural policy and fertilizers distribution. The new Cabinet introduced a Structural Adjustment Program in 1991, and maize production was influenced by the price and availability of chemical fertilizers. Decreasing fertilizer supply led to a low maize yield and in the following season they tried to expand the area of Citemene fields against food shortage. Elderly women who regarded the Citemene system as important for subsistence, contributed to the food security within the village. In the 1980's the elderly female households were supported by younger relatives who opened Citemene fields extensively, but in 1995 they shared their staple food with their younger relatives. The Bemba consistently persisted in food self-sufficiency by ctemene system and coped flexibly with the prevailing socioeconomic conditions.
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4. KAKEYA, M. and Y. SUGIYAMA 1985 Citemene, finger millet and Bemba culture: A socio-ecological study of slash-and-burn cultivation in Northern Zambia. African Study Monographs, Suppl. 4: 1-24.
5. KAKEYA, M. and Y. SUGIYAMA 1987 Agricultural changes and its mechanism in the Bemba villages of Northeastern Zambia. African Study Monographs, Suppl. 6: 1-13.
6. KAKEYA, M. 1994 Slash-and-burn agriculture society and leveling mechanism. In: Living on the earth Vol. 2. Cultural adaptation to resources. (OTSUKA R. eds.) Yuzankaku Publishing Co. (Tokyo) 121-145. (In Japanese)
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Makarikarigrass is relatively tolerant to various environmental stresses such as drought and low temperature among tropical grasses, and the cultivar (Yukijirushi-kei) showed phenotypic variations in these properties. After sowing in 1995, 17 lines from the overwintered plants were selected as one plant for one line in May, 1996. Each line was replanted by vegetative propagation of the overwintered plants every May, during the period 1996-1999 at Sumiyoshi which is characterized by a sandy soil with a low water-holding capacity (WHC) and every May, during the period 1998-1999 at Kibana which is characterized by a loamy soil with a high WHC. Several plant characters such as aboveground dry matter weight (DMW), total tiller number (TTN), mean tiller weight (MTW) and percentage of elongated tillers (PET) at three cuttings, and overwintering ability such as percentage of overwintered plants (POP) and regrown tiller number (RTN) were determined for 17 lines during a 4-year period from 1996-1999. Drought tolerance was assessed by the growth potential in the dry season at the two sites. The DMW, MTW and PET were the highest at the second cutting, while TTN increased with the cutting practice at both sites every year. Variation in plant characters among the lines generally increased with the cutting. Correlation coefficients of plant characters in all the lines among years were positive except for those at Sumiyoshi under drought conditions. The POP and RTN were higher and their variations among the lines were lower in 1998 and 1999 under the mild winter conditions than in 1997 and 2000 after a colder winter at Sumiyoshi. Correlation coefficients of plants characters with POP were only positive at Sumiyoshi under drought conditions in 1998. These results suggest the presense of a closely positive correlation between high drought tolerance, represented by the high growth potential under the drought conditions and high tolerance to low temperatures, represented by the high overwintering ability. Selection of makarikarigrass lines with superior growth characters, drought tolerance and overwintering ability was found to be possible.

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It is important to improve the efficiency of fertilizers especially nitrogen (N), for rice cultivation in sandy soil under rainfed conditions, such as in the inland valley swamps (IVs) of West Africa. We conducted pot experiments using JapaneseMasasoil, a sandy Entisol, as the test soil. It has similar physicochemical characteristics to those of West African IVs soils. We also compared the results under submergence conditions with negligible leaching with those under poor water control, i, e., alternate leaching but without submergence. Polyolefin-coated urea (LPSS-100), which is a controlled-release N fertilizer with delayed release properties, was used in the experiment with IR36 (an Indica type ofOryza sativaL.) . The plant height and the tiller number of the LPSS-100-treated plants initially slowly increased for about 40 days. Thereafter, they both increased more rapidly compared to the urea-treated plants. This was a significant finding because urea was used in two split applications while for LPSS-100 there was only one basal application. LPSS-100-treated plants showed a higher N uptake throughout the growth cycle of the plant than the urea-treated plants. As a result, the LPSS-100-treated plants gave a significantly higher grain yield under both submerged conditions and under alternate leaching. Also the LPSS-100-treated plants had a higher N recovery averaging 62.9% as against 30.7% for the urea-treated plants. The agronomic N-use efficiency of LPSS averaged 36g⋅g^-1N as against 20g⋅g^-1N for the urea-treated plants at 6g N⋅m^-2. The difference in effect of the conditions of water management on the efficiency of both urea and LPSS-100 was not significant. But the overall performance of LPSS-100 was still superior to that of urea.

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We surveyed rice fields in East and Northeast Thailand, from Bangkok to Phitsanulok, and in rural areas near Hanoi, Da Nang and Can Tho, in Vietnam, to study the distribution and density of apple snails with shells ≥ 20mm. We also asked farmers and agricultural engineers when the snails were observed for the first time in their fields; how high the snail density was there; how much damage the snails caused to cultivated plants; which methods of control they had applied; and whether the snails were used, e.g. for food or weed control. Snails were distributed at low densities, usually ≤ 1.0/m², in Thailand, but at higher densities in Vietnam. Accordingly, the proportion of the locations with a serious snail problem was lower in Thailand (19%) than in Vietnam (90%) . Despite this difference, in both countries, there were locations where snails at densities of ≥ 1.0/m²caused serious damage. These findings suggest that a density estimate in a given field can provide a rough prediction of the damage by the snails: If the density is 1.0/m²or higher, the snail problem would be serious; if lower, it would be negligible. This density can be considered as a tolerable pest density. Hand-picking was used predominantly for controlling the snails at locations with slight damage in Thailand, and at all the locations in Vietnam. This method was successful to some extent in Vietnam. Chemical control was applied less frequently. In both countries the snails were seldom used, because of their soft texture and poor taste. Hence, control of the snail through capture is not likely to succeed.

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Physico-chemical properties of Vertisols in the Mwea area, the major irrigated rice area of Kenya, were investigated to develop recommendations for soil and nutrient management for intensive rice cultivation. Soil depth ranged from 0.8 to 1.8 m with dark clay layers with a heavy texture predominated by montmorillonite. Only a weak horizon differentiation was recognized in the clay layers except for a slight change in the structure with depth. Carbonates as nodules and concretions were commonly detected in deep to shallow layers. The soil chemical fertility was estimated to be medium to high in terms of major essential elements in general, except for K whose amount was found to be rather low in some areas. Available N level was medium to high for Vertisols, but it was obvious that efficient N application was essential to achieve a high yield standard considering the range of soil available N content.
Low yield was often associated with a low topographic position of the fields. In the fields with poor drainage mostly found in depressed areas, strong reduction of soil and high base concentration might disturb the root activity for nutrient uptake.
From the physical viewpoint, difficulty in plowing was a major constraint. Dry tillage could be an option to minimize water percolation into deep layers along cracks to maintain the trafficability. Incorporation of organic matter such as rice straw or upland crop residues is being tested to improve the friability of soil for better workability in dry tillage and drainage, which may also contribute to the recycling of nutrient sources like K.

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We carried out this experiment to examine the effects of exogenous GAs, ABA and uniconazol-P on the growth of water yam (Dioscorea alata L.) in order to analyze the distinctive growth response of water yam to GA treatment. Foliar application of GAs at the early growth stage inhibited the growth of the above-ground parts, and the inhibition effect continued for a certain period. Enlargement of the tubers began immediately after GA treatment and this promotive effect continued until the tubers of the non-treated plants started to enlarge under natural day length. In all the examined strains from different geographical areas and with variations in earliness, growth inhibition of the above-ground parts and promotion of the enlargement of tubers by GA treatment were observed. It is assumed that water yam showed a wide specific growth response to GAs. Also it was revealed that the growth pattern of the branches differed in each strain and GAs inhibited the development of branches in all the strains. As a result, the plant type changed. Uniconazol-P promoted the growth of above-ground parts and inhibited the enlargement of the tubers. However, ABA did not affect the growth of the above-ground parts. Since ABA inhibited the enlargement of the tubers, ABA also seemed to be associated with the growth of water yam. Root treatment with GAs, ABA and uniconazol-P exerted the same effect as when these substances were applied to foliar parts.

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It is well known that jasmonic acid and related compounds are plant growth regulators associated with the growth of yam plants. Gibberellins (GA₃) and abscisic acid (ABA) are also considered to play a role in the growth of yam (Dioscoreaspp.) . Therefore, the effects of these three plant growth regulators on the growth of plantlets and enlargement of microtubers were examinedin vitro. JA-Me and GA₃promoted the enlargement of microtubers, while ABA exerted an inhibitory effect on them. Combination of ABA with GA₃led to a decrease of the inhibitory effect of ABA and the promoting effect of GA₃, respectively. The similar results were obtained in the combination of ABA and JA-Me. These results indicated that ABA exerted an antagonistic effect on JA-Me and GA₃ in the enlargement of microtubers. No synergistic effects of JA-Me with GA₃were observed. On the other hand, ABA inhibited the stem elongation of yam plantlets. Furthermore, GA₃, which generally promotes stem elongation in other plants, also strongly inhibited it. These results suggested that water yam showed an unusual growth response to GA₃.

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Sugarcane quality was estimated using a Near Infrared (NIR) Spectrophotometer and a conventional method. Cane juice, milled and dried cane stalks, and shredded cane stalks were used as samples in NIR examinations for measuring the Brix value, sugar and fiber contents. Cane juice samples were used for the measurement of the Brix value and sugar content, and milled and dried cane stalks or shredded cane stalks for the measurement of the fiber content in addition to the Brix value and sugar content. The specific wavelength of 1438nm, which corresponds to the sucrose factor, was commonly required in all the Brix or sugar content measurements, while the specific wavelength of 2352nm for the cellulose factor was commonly required in all the fiber content measurements. All these samples were found to be suitable for a precise estimation with cane juice samples providing the most precise one. Shredded cane samples required less time than milled and dried cane samples for estimation, as they could be simply prepared without drying or milling. It is suggested that sugarcane quality using shredded cane samples could be estimated precisely and quickly by NIR spectrophotometry.

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Flower-color evaluation systems for practical classification of the cultivars of flowering lotus (Nelumbo spp.) were investigated. The determination of the flower color was carried out 2 days after flowering using a color-meter for 3-5 flowers of each cultivar. Considerable differences were observed in the values of a^* and b^* in the L^* a^* b^* color system among the cultivars. It was necessary that 5 petals in every flower be piled up to reduce the values of the coefficient of variation obtained measured by the color-meter. Some of the cultivars in the blotch-color group and the nail red group, which showed a non-uniform color distribution, actually deviated from the respective groups. Cluster analysis was carried out for the following 6 factors; values of a^* and b^* in the L^* a^* b^* color system, deviation of distribution of anthocyanin in the petals, degree of distinctiveness of the streaks, number of petals of a flower and flower size. Ninety-five cultivars were divided into the following 7 color groups; yellow, white, light yellow, blotched, nail red, pink, and red.

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