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High temperature stress during grain-filling period is one of the major environmental constraints limiting the grain yield of wheat in Bangladesh. Crop growth response and relative performance of yield components of ten wheat genotypes were studied in two temperature conditions in glass rooms in a Phytotron to identify the genotype tolerant to high temperature stress. A favourable day/night temperatures of 15/10, 20/15, and 25/20 0 C were maintained from sowing to 60 days after sowing (DAS), 61 to 80 DAS and 81 DAS to maturity, respectively, in one glass room (G 1 ); whereas day/night temperatures in another glass room (G 2 ) was always maintained at 5°C higher than that of G 1 . Green leaf area and number of tillers in different times, number of days for the occurrence of major crop growth stages, relative performance in yield components, grain yield and heat susceptibility index were estimated following the standard methods. The higher temperature enhanced plant growth, flowering, and maturation. Thus the number of days to booting, heading, anthesis, and maturity of wheat were significantly decreased that varied among the genotypes. Green leaf area and productive tillers/plant were drastically reduced in time under high temperature. The reduced number of grains/spike and smaller grain size resulted from drastic reduction in growth duration were responsible for the yield loss of wheat at high temperature. Out of ten wheat genotypes, three were characterized as high temperature tolerant based on their relative performance in yield components, grain yield and heat susceptibility index.

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Various types of soil physical properties are affected by texture and structure. Our objective was to determine aggregate structure effect on the soil dielectric property of an Andisol measured by time domain reflectometry (TDR). The relationships between volumetric water content (θ) and dielectric permittivity (ε) for both a wet‐sieved aggregate and its crushed sample were examined and compared. In the θ–ε relationship for 0.1‐ to 2.0‐mm‐diam. wet‐sieved aggregates, the gradient of the θ–ε curve moderately changed at a volumetric water content (critical water content), although this property disappeared when we crushed the aggregate structure. Furthermore, the critical value corresponded to the water content of the plateau in a bimodal‐type water retention curve. We suggest that effects of aggregate structure on a soil's dielectric property are involved in the aggregate sizes, the configuration of water in aggregates, the processes of water filling in intra‐ and interaggregate pores, and the low ε value of bound water adsorbed on soil surfaces.