Fumihiko Adachi

Effect of soil compaction on dry matter production and water use of rice (Oryza sativa L.) under water deficit stress during the reproductive stage.

Abstract The effect of a long term of soil compaction on dry matter production (DMP) and water use in rice cultivated under limited water supply during the reproductive stage is unknown. Our objectives were to determine which of the transpiration (Tr) or water use efficiency (WUE) is dominant in determining DMP under compacted and desiccated soil conditions. When irrigation in the period around the reproductive stage was terminated in artificially compacted and non-compacted fields, the rate of suppression of DMP by soil compaction was similar in the three rice cultivars, but DMP was higher in drought resistant cultivars having deep root density at the heading stage. Six cultivars were grown in pots of 1.0 m in depth containing the soils of three levels of soil bulk density (SBD). Water supply was restricted by keeping the water table in the pot deep without irrigation during the reproductive stage. DMP and Tr in all cultivars decreased with increasing SBD, and a close relationship was seen between DMP and Tr. WUE was thus a fairly stable factor for all cultivars examined. Tr was positively correlated with root length density and was relatively maintained at a high SBD in drought-resistant cultivars having a higher root length density. We concluded that water shortage under compacted soil conditions during reproductive stage suppressed the DMP, and DMP suppression accompanied a reduction of Tr due to poor root development rather than the reduction of WUE. In the drought-resistant cultivars reduction of DMP was relatively small due to their highly developed root systems that allowed high water absorption from the deep layers in the compacted soil.

Assimilate Supply as a Yield Determination Factor in Spring Wheat under High Temperature Conditions in the Mediterranean Zone of South-East Turkey

Abstract Wheat in the Mediterranean zone often encounters high temperatures during the terminal growth stage. This study investigated whether assimilate supply by source-function plays a dominant role in determining grain production in spring wheat exposed to high terminaltemperatures in the Mediterranean zone of south-east Turkey. The spring wheat cultivar Adana99 was grown under irrigated conditions sowing according to the current schedule (CS plants) and late-sowing (LS plants) for two years. Grain yield of CS plants, which were subjected to relatively lower temperatures during the terminal growth stage, was higher than that of LS plants, which were subjected to relatively higher temperatures. A high temperature in the post-anthesis period accelerated leaf senescence and reduced radiation-use efficiency. Halving the plant density at anthesis, which increases assimilate supply to grains, significantly increased the grain dry weight (GDW) and whole plant dry weight (WPDW) in the post-anthesis period. Grain filling percentage (F%, observed/final GDW) in thinned plants, which was regarded as potential F%, showed a single logistic equation based on cumulative temperature after anthesis, regardless of post-anthesis temperatures. In the LS plants, the daily increase in WPDM ( Δwpdw) decreased, but the peak of an increase rate of potential GDW estimated from F% was shifted to earlier-filling stage, resulting in reduced GDW at harvest. The final GDW in both years closely correlated with the estimated Δwpdw in the grain-filling period. These results suggest that source-function for assimilate supply in the post-anthesis period is one of the important yield-determining processes in spring wheat subjected to high temperatures.