Rice Growth Period Research Articles

青森県内水稲作の地域性 3. 気象要因特に気温を中心に

青森県内水稲作の地域性 3. 気象要因特に気温を中心に

Varietal differences in the response of rice plants to nitrogen-dressing with special reference to patterns of cange in nitrogen content of roots at successive growth stage.

Varietal differences in the total nitrogen content of the roots or rice plants grown under 2 nitrogen dressing regimes (low fertilizer : 2.5 kg-N/10 a, high fertilizer : 7.5 kg/10 a) were investigated in 1984 by using the monolith method. Varietal differences in the decrease of the total nitrogen content of the roots and leaf blades as growth advanced were not recognized. The change in the amount of total nitrogen in the roots varied with cultivars. The cultivars used in this experiment can be divided into four types according to their patterns of change in the amount of total nitrogen in the roots, namely; a) those which showed no marked change in the amount of total nitrogen regardless of fertilizer levels and of growth stage, like Sen-ichi and Norin 3 (A type), b) those which showed a significant decrease in the amount of total nitrogen with the increase in the amount of fertilizer dressed, like Jyukkoku, Asahi and Futaba (B type), c) those which showed a proportionate increase with the amount of fertilizer dressed, like Takenari (C type), and d) those which showed variable response, where in the amount of total nitrogen was higher in the low fertilizer plot than in the high fertilizer plot in the early growth stage (July to August) and vice versa in the later stages (August to September) (D type). The general result of this study tends to suggest that there is a close significant correlationship between the amount of total nitrogen in the roots and root dry weight throughout the growth period of rice. Cultivars of A, B, and C types are distinct from each other on the regression line.

Potatoes and the Nutritional Ecology of Crested Porcupines in a Desert Biome

Taking non-transgenic parental rice as the control, and by using 13C pulse-chase labeling method coupled with phospholipid fatty acid (PLFA) analysis, this paper studied the effects of transgenic Bt rice on the microbial diversity in rhizosphere soil. The results showed that in the rhizosphere soils of transgenic Bt rice and its non-transgenic parent, saturated PLFAs and branched PLFAs were the main, followed by monounsaturated PLFAs, and polyunsaturated PLFAs. A significantly lower amount of Gram-positive bacterial PLFAs and a higher amount of Gram-negative bacterial PLFAs were observed in the rhizosphere soil of transgenic Bt rice at its seedling, booting, and heading stages, as compared with the control. In the whole growth period of rice, transgenic Bt gene had no significant effects on the fungal and actinomycete PLFAs in rhizosphere soil, and no significant difference was observed in the rhizosphere soil 13C-PLFA content between transgenic Bt rice and its non-transgenic parent. These findings indicated that the insertion of exogenous cry1Ab gene into rice only had temporary effects on the microbial community composition in the rhizosphere soil of rice.

Seasonal occurrence of the yellow stem borer Scirpophaga incertulas (Walker) on deepwater rice in Bangladesh and Thailand

Deepwater rice is grown in South and Southeast Asia on 11 million hectares flooded deeply during the monsoon. Surveys for the incidence of stem borers in deepwater rice in Bangladesh from 1977 to 1980, and in Thailand during 1981 and 1982, showed that borer incidence and species composition were remarkably similar. Scirpophaga incertulas (Walker) usually comprised more than 90% of the borer population and was almost exclusively present during the main flooding period. Chilo polychrysus (Meyr.) comprised 11% and Sesamia inferens (Walker) 6% of the population in the pre-flood and ripening stages. Low borer activity in the early part of the season was explained by a low nucleus population, the synchronous planting of deepwater rice, and severe moisture stress and high temperatures in the pre-flood period. In Bangladesh, a severe drought in 1979 limited Scirpophaga incertulas populations to unusually low levels until the flowering stage. In Thailand, drier conditions, the lack of an intervening rice crop in the dry season and a longer pre-flood period, appeared to severely restrict early season borer activity. The onset of flooding and stem elongation provided a more favourable environment for S. incertulas. Borer activity increased steadily during the first 3–4 months of flooding, to average 23% damaged stems (26 m −2) and 13 borer immature stages/100 stems (13 m −2) by the flowering stage. Borer activity continued at about the same level as the water receded, to reach maximum annual levels of 38–44% damaged stems (35 m −2) at the late-ripening stage. At harvest, 60% of the fields were at outbreak level (>40% damaged stems). Such high levels of damage are explained by the long growth period of deepwater rice, favourable weather during the flooding period, and the optimum habitat of the elongated stem. S. incertulas populations then crashed to low levels; the larvae entering diapause in the field stubble. Although related to actual damage, the deadheart and whitehead symptoms grossly under-estimated the extent of stem damage.

Proposal of a Method for Analysis of Free Amino Acids in Paddy Soils and Investigation on Behavior of Them in Rice Growth Period

Proposal of a Method for Analysis of Free Amino Acids in Paddy Soils and Investigation on Behavior of Them in Rice Growth Period

Atmospheric nitrogen fixation by photosynthetic microorganisms in a submerged Philippine soil

Abstract Photosynthetic nitrogen-fixing microorganisms help maintain the nitrogen level of soil in rice paddies when environmental factors favor the growth of microorganisms. Our studies showed that blue-green algae in particular have a significant role in nitrogen-fixation in light. The most active nitrogen-fixation by microorganisms occurred in the soil shortly after it had been submerged under light. The longer the submergence, the less nitrogen microorganisms were fixed. In a greenhouse experiment, the fixed nitrogen appeared not to be immediately available to the rice plant. The amount of nitrogen that can be fixed in the field by nitrogen-fixing microorganisms in paddy water was estimated using the acetylene reduction method during the rice-growing period. The amount of nitrogen fixation by these microorganisms is not sufficient to account for the amount of nitrogen uptake by rice during the rice-growing period.