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Rice (Oryza sativaL.) is generally grown continuously submerged in lowland soils and under rainfed conditions in upland soils. The objective of this study was to relate transpiration rate and leaf water potential to relative water content. This information may be useful in predicting the effect of soil moisture stress on growth and yield. Rice variety ‘IR‐8’ was grown in the greenhouse for 50 to 60 days under submergence and N⅓ bar soil matric potential, and then allowed to wilt. The pressure potential of leaves approached zero at a total water potential of about −19.5 bars, corresponding to 0.33 relative water content. Leaves experienced a change in cell elasticity at about 3 bars pressure potential and −10 bars total water potential Transpiration rate decreased with leaf water potential, but it was independent of depletion of soil moisture content above 0.21 and 0.18 for plants grown in submerged and unsaturated soil conditions, respectively. These moisture contents correspond to −0.8 bar and −2.0 bars matric potential. Further depletion in moisture content of both soil moisture regimes resulted in a marked decrease in leaf water potential and in transpiration. Trans. port of water in the rice soil‐plant system was affected more by plant factors under flooded conditions than under unsaturated soil conditions.

The potential of new corn hybrids in India is not obtained because of waterlogging. A field experiment on a Mollisol‐udoll soil was conducted 1) to study the response of five corn varieties (cultivars) to waterlogged conditions and 2) to determine the critical growth stages and duration of waterlogging at which yield is significantly reduced. Waterlogging affected growth rate, nutrient uptake, a number of other physiological processes, and yield. Waterlogging (48 hours and 72 hours) at knee‐high stage and tasselling stage retarded the growth of all the varieties except ‘Ganga‐2’ and submergence for 72 hours significantly reduced the uptake of N and K and increased P uptake in all the varieties. Calcium and Mg uptake were unaffected. The grain yield of varieties was found in the decreasing order of ‘Jaunpur’ < ‘Kisan’ < ‘Vijay’ < ‘Ganga‐7’ < Ganga‐2. Soil flooding at knee‐high stage was found to be more harmful than at tasseling stage. The critical limits of waterlogging at knee‐high stage were 72 hours for Ganga‐2 and 48 hours for other varieties. Flooding for 72 hours did not reduce the yield of Ganga‐2 at tasselling stage but yield of other varieties was significantly decreased. Ganga‐2 was more tolerant to waterlogging because it developed maximum gas spaces and an extensive adventitious root system at the surface of the water under waterlogged conditions.

The magnetic susceptibility of lateritic soils and clays has been determined. A linear relationship between specific magnetic susceptibility and iron oxide content of kaolinitic and allophanic soils and clays has been observed. Montmorillonite and magnetite-bearing soils have shown high magnetic susceptibilities which were not related linearly to their iron oxide contents. Feand Fe ion substitutions in the octahedral position of 2:1 types of clays were thought to be the probable cause of high magnetic susceptibility of such soils. The high values obtained for the latter may be attributed solely to the ferromagnetic property of magnetite. The type of bonding of Feion in octahedral coordination was investigated through spin-only moment (u. eff.) determinations. It was found that substitution of less than half a mole of Feion per unit cell in 2:1 types of clays appears to form electrostatic bonding (i.e., spin-free, sp3d2bonding), while more than half a mole of Feion per unit cell shows the covalent type of bonding (i.e., spin-paired, d2sp3bonding). The diamagnetic, paramagnetic, and ferromagnetic nature of kaolinite, montmorillonite, hematite, and magnetite, respectively, has been evidenced.

Growth responses of a rice root system to particle and pore size distributions were assessed in eight soil mixtures artificially synthesized from separated clay, silt, and sand-sized quartz powders, under a controlled optimum, submerged (3 ± 1 centimeters) soil temperature regime of 37–25°C. Moisture retention characteristics were utilized for calculating the average macropore size and effective pore size densities of the soils

Rice (Oryza sativaL.) is grown either in continuously flooded “lowland” soils or under rainfed conditions in “upland” soils. The objective of the study was to determine whether there are differences in resistance to water transport between plants grown in flooded and non‐flooded soils. This information may be useful in understanding the plant‐water relations under two cultural practices. In a greenhouse, rice variety ‘IR‐8’ was grown under flooded and 0.33 bar soil suction for 45 to 50 days. The resistance to water transport in different plant parts and in the whole plant was measured by a transient flow method. The effect of an increased air saturation deficit from 15 mb to 45 mb on transpiration rate and on leaf water potential was studied in a controlled environment chamber. The resistance to water transport in the non‐flooded plants was nearly twice as high as in the flooded plants. The non‐aerenchymatous roots of non‐flooded plants had about 17 times more resistance than aerenchymatous roots of flooded plants. The gradient between leaf and soil water potential increased markedly when plants were exposed to high air saturation deficit; however, the transpiration rate remained almost constant. These studies indicate the existence and development of large resistances to water transport in rice plants.

Information is lacking on the performance of the rice plant due to variations in temperature regimes in association with other soil physical properties. This investigation, carried out under controlled greenhouse conditions, evaluated the influence of temperature and mechanical impedance of soil, as well as of their interaction, on root and shoot growth of rice (Oryza sativaL. ‘Taichung Native 1’). Four submerged soil temperature regimes (27 to 15 C, 32 to 20 C, 37 to 25 C and 42 to 30 C) thermoregulated in water baths, indicated that the maximum root and shoot growth of rice occurred at 37 to 25 C. Irrespective of the bulk density of soil, the total number of roots at the base and the dry weight and volume of the rice root system significantly increased as the submerged soil temperature regime increased from 27 to 15 C to 37 to 25 C, but decreased at 42 to 30 C. Multiple regression analysis indicated that the number of degenerated roots increased with the increase in submerged soil temperature regime, but decreased with the increase in bulk density of the lateritic sandy loam soil. The multiple correlation coefficient between these three variables was significant at 1% level (R=0.79). With increase in bulk density from low to medium, the dry weight of shoot and root, and the number of roots at the base significantly increased at 27 to 15 C and 42 to 30 C, but decreased at 37 to 25 C in all the three soil textures studied. However, when the bulk density was increased from medium to high levels, the shoot and root growth parameter decreased under all temperature regimes.

Rice plants of a Taiwanese indica variety, ‘Taichnng (Native) 1,’ were grown in a clay loam soil for 6 weeks from seeding under normal conditions of a greenhouse and then transferred to controlled temperature water baths where cyclic soil temperatures were maintained till harvest. Water level was maintained at a depth of 5 to 7 cm above the soil surface. The temperature cycles as characterised by their maxima and minima were 22/10, 27/I5, 32/20, 37/25 and 42C/30C. The experiment was first conducted during winter months and repeated during summer months except that 22C/10C cycle was not included. Soil temperature greatly influenced vegetative and reproductive growth of the plant. Nearly similar effects of different soil temperature regimes were observed during winter and summer although the difference of about 11 or 12C in aerial temperatures existed. Highest grain yield was obtained at 32C/20C which resulted from larger number of tillers, panicles, and spikelets, lower spikelet sterility and greater hundred grain weight than at lower and higher temperatures. A dose correspondence was observed between root and shoot growth. Greater uptake of nutrients was associated with larger root system. There was a tendency for grain to be higher and straw to be lower in N, P and K concentration at 32C/20C than at lower and higher temperatures. NPK content of the grain was significantly correlated with grain yield. The direct effects of soil and water temperature on shoot growth were also probable since tiller and panicle primordia develop at the basal portion of the stems which remained submerged under soil‐water.