Hisayoshi Hayashi

Influence of day length before and after the start of anthesis on the growth, flowering and seed-setting in common buckwheat (Fagopyrum esculentum Moench)

Abstract The influence of day length before and after the start of anthesis on the growth, flowering process, and seed -setting of common buckwheat (Fagopyrum esculentum Moench) was investigated to determine the effect of day length at various growth stages. Exposure to long days (15 h in 2001 and 16 h in 2000) made the node position of the first flower higher, delayed the start of anthesis, decreased the rate of successive flowering, increased the number of nodes and flower clusters on the main stem, and prolonged the main stem elongation period. It increased the number of flowers per flower cluster, but decreased the seed-setting ratio and the number of seeds. The critical day length varied with the cultivar and the growth parameter. ‘Miyazakizairai’ (autumn eco-type) showed significantly greater responses to long days than ‘Shinanonatsusoba’ (summer eco-type). The day length before the start of anthesis significantly influenced on the main stem elongation and flowering process thereafter. This suggests that the day length is a more critical factor for the differentiation than the growth of the flower bud. The seed-setting ratio was influenced both by day lengths before and after the start of anthesis. The 15 h day length before the start of anthesis and around 12 h day length thereafter increased the number of double and multiple clusters in ‘Shinanonatsusoba’ and long clusters in ‘Miyazakizairai’, resulting in an increase in the number of seeds per cluster. Day length did not influence either the form or weight of seeds.

Increase in soil carbon sequestration using rice husk charcoal without stimulating CH4 and N2O emissions in an Andosol paddy field in Japan

Abstract Biochar application has been recognized as an effective option for promoting carbon (C) sequestration, but it may also affect the production and consumption of methane (CH4) and nitrous oxide (N2O) in soil. A 1-year field experiment was conducted to investigate the effects of rice husk charcoal application on rice (Oryza sativa L.) productivity and the balance of greenhouse gas exchanges in an Andosol paddy field. The experiment compared the treatments of rice husk charcoal applied at 10, 20 and 40 Mg ha−1 (RC10, RC20 and RC40, respectively), rice husk applied at 20 Mg ha−1 (RH20), and the control (CONT). Rice straw and grain yields did not significantly differ among the treatments. The seasonal cumulative CH4 emissions were 38–47% higher from RC10, RC20 and RC40 than from the CONT. However, the increases were not in proportion to the application rates of rice husk charcoal, and their values did not significantly differ from the CONT. On the contrary, the RH20 treatment significantly increased the cumulative CH4 emission by 227% compared to the CONT. The N2O emissions during the measurement were not affected by the treatments. As a result, the combined global warming potential (GWP) of CH4 and N2O emissions was significantly higher in RH20 than in the other treatments. There was a positive linear correlation between C storage in the top 10 cm of soil and the application rate of rice husk charcoal. The increases in soil C contents compared to the CONT corresponded to 98–149% of the C amounts added as rice husk charcoal and 41% of the C added as rice husk. Carbon dioxide (CO2) fluxes in the off season were not significantly different among RC10, RC20, RC40 and CONT, indicating that C added as rice husk charcoal remained in the soil during the fallow period. The CO2 equivalent balance between soil C sequestration and the combined GWP indicates that the rice husk charcoal treatments stored more C in soil than the CONT, whereas the RH20 emitted more C than the CONT. These results suggest that rice husk charcoal application will contribute to mitigating global warming without sacrificing rice yields.

Influence of Day Length on Stem Growth, Flowering, Morphology of Flower Clusters, and Seed-Set in Buckwheat (Fagopyrum esculentum Moench)

Abstract The effects of day length on main stem growth, flowering, morphology of flower clusters and seed-set were examined in three buckwheat cultivars Shinanonatsusoba (summer eco-type), Miyazakizairai (autumn eco-type) and BLO 1999 (a long cluster line which usually develops DM clusters at Kade Research Ltd., Canada). Long-day treatment prolonged the stem elongation period, elevated the first flowering node, delayed the first flowering day, increased the numbers of nodes, flower clusters and flowers on the main stem, and decreased the increase rate of flowering-cluster number, the number of seeds and the seed-set ratio on the main stem. It also increased the frequency of DM clusters, the length of the flower clusters and the number of sub-flower-clusters per cluster in Shinanonatsusoba and Miyazakizairai as well as in BLO 1999. The effects of day length varied among the growth parameters and there were three types of responses to day length. The difference between the summer and autumn eco-type cultivars in the responses to day length was elucidated in four groups of parameters; (1) main stem elongation; (2) first flowering node and first flowering day; (3) increase rate of flowering-cluster number on the main stem; and (4) the number of seeds and seed-set ratio.

Rice yield and soil carbon dynamics over three years of applying rice husk charcoal to an Andosol paddy field

Abstract Rice husk charcoal (RC) produced from the pyrolysis of rice husk (RH) can be one of the cost-effective biochars for use in rice-based farming systems. This study investigated changes in rice yield and soil carbon sequestration over three years of RC application to an Andosol paddy field. The treatments were RC application at 0.02, 0.2, and 2 kg m−2 (RC0.02, RC0.2, and RC2, respectively), RH application at 0.2 kg m−2 (RH0.2), and a control with no RC or RH application (CONT). The results showed that RC2 increased culm length by 4% and straw weight by 14% on average over the three years. These increases in plant growth coincided with a higher level of silicon uptake by the rice plants, although they did not significantly affect grain yield. The soil carbon content was progressively increased by RC2 over the three years, whereas it was not significantly affected by RC0.02 or RC0.2. A considerable amount (>72%) of the applied carbon with RC2 remained in the soil by taking account of its downward movement below the 10 cm layer of the paddy field after three consecutive years of RC application. We conclude that rice husk charcoal application to Andosol paddy fields is an effective option for increasing carbon sequestration. Furthermore, the increase in silicon uptake by rice plants suggests that rice husk charcoal can also be functioning as a silicon fertilizer.