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The cultivation period of cassava in Kagoshima, Japan, which belongs to the temperate zone, is limited by the low temperature in winter. To maximize productivity under this limited period, investigations were conducted on the gas exchange rate and production structure relating to light utilization in a plant community of cassava grown under different nitrogen fertilization conditions. Fertilization either at planting or three months after planting significantly increased stomatal conductance in the upper canopy and root dry weight compared to the control. In addition, the dry matter distribution to stem and root dry matter rate of initial fertilization treatment were significantly higher, and the dry matter distribution to root of the latter fertilization treatment tended to be higher than that of the control. However, light transmittance at 80 cm below the top of the canopy was almost the same as that at the ground surface, which was a common tendency among the treatments. In conclusion, it was revealed that the effects of fertilization on yield were mainly the increase in the gas exchange rate of individual leaves and the change of dry matter distribution rather than an improvement in light transmittance.

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During rainfed upland rice (Oryza sativa) cultivation, unpredictable drought events can hinder the rice growth. Although drought tolerance is a reported effect of seed priming treatment, we hypothesized that plants from primed seeds would die because they would begin to emerge in dry soil. We also expected that nonemerged primed seeds would show decreased seed vigor because their metabolism was activated by priming before sowing. Therefore, we investigated the vigor of hydroprimed and nonprimed seeds during prolonged drought after sowing during upland rice cultivation. A field experiment was conducted on a rainfed upland field that had insufficient rainfall at the beginning of the season. Plant emergence, establishment, and vigor in resown nongerminated seeds were also investigated. A subsequent growth chamber experiment was conducted to investigate the relationship between sown seed deterioration, soil moisture, and temperature. Contrary to the hypothesis, plants from primed as well as control seeds could survive under prolonged drought after emergence. In the nongerminated primed seeds, oxidative damage was increased. However, the percentage of plant emergence in resown seeds did not differ between treatments. Overall, the performance of primed seeds was better than or similar to that of the control seeds. In conclusion, primed seeds have advantages even under extreme drought conditions in rainfed upland fields.

No abstract