Quantifying growth dynamics in rice (Oryza sativa L.) is important for precision design and diagnosis in cultural management. The primary objective of this study was to develop a general knowledge-based model to design the time-course growth dynamics including stem number, leaf area index (LAI) and aboveground dry matter accumulation with desired target yield under different conditions in rice. Driven by physiological development time (PDT)-based growing degree-days (GDD), the fundamental algorithms of rice growth indices, which vary with the variety, environmental factors and production levels, were formulated from the existing literature and research data. The stem number curve was established according to the dynamic pattern of the stem development and the principle of determining stem number from final panicle number. Under the principle of realizing the maximal photosynthetic production during forty days before and after heading, we obtained the optimum LAI at heading was calculated, and the LAI dynamic from the ratios of LAIs at different growth stages to optimum LAI at heading with linear interpolation method. The aboveground dry matter accumulation curve was described by a logistic curve. Case studies with the typical data sets and variety types at different eco-sites indicated a good performance of the model system, with the root mean square error (RMSE) of 2.5×10⁴ ha^-1, 0.37 and 700 kg ha^-1, for the stem number, LAI and aboveground dry matter accumulation, respectively. This model overcomes the weakness of poor spatial and temporal adaptation of traditional rice management patterns and expert systems.

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Productivity of the soil with waste material (WM), i.e., bagasse, coir dust, rice chaff and rice straw decomposed for two months at various temperatures and soil moisture were investigated by analyzing the chemical properties and growth of maize cultured on the soil for 45 days. The soil with decomposed WM (WM soil), tended to show lower pH values than the soil without WM soil (control) as a whole. The values of electric conductance were higher in WM soil, especially in the soil with decomposed rice chaff and rice straw referred to as rice-chaff and rice-straw soils, respectively. The total N content tended to be higher in the WM soil except for coir dust soil. The total C content tended to be higher in all WM soils. The difference in the content of total N and total C between WM and control soils was remarkable in bagasse soil. The change of the chemical properties of the soil did not apparently correlate with the rate of CO₂ generation during incubation of WM soils, but pH, electric conductance, content of total N and total C contents were higher in the soils generating CO₂ at a rate of 40 to 80 ppm min^-1, in bagasse or rice straw soils. The dry matter production of maize on WM soils was positively correlated with the rate of CO₂ generation. It was suggested that the WM soils generating little CO₂, such as the soil with bagasse or rice straw decomposed in a dry condition, tended to inhibit maize growth owing to low pH and shortage of available nitrogen by rapid decomposition just after the start of maize growth. The wet WM soils generating CO₂ format a rate of 40 to 80 ppm min^-1, e.g., bagasse and rice straw soils might be favorable for dry matter production of maize.

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The ¹⁵N natural abundance method has been widely used for evaluation of symbiotic N₂-fixation. The method inevitably requires a reference plant that reflects soil derived δ¹⁵N similar to that in a N₂-fixing target plant, for estimating the contribution of fixed N₂. However, it is often difficult to select a suitable reference plant. Recently, an alternative method was proposed using the difference in δ¹⁵N values between shoots and nodulated roots, which did not require a reference plant per se. Whether this method is applicable to a wide range of N₂-fixing plants having different growth habits and symbiosis types remains to be verified. To test the applicability of this method for perennial plants, we examined the difference in δ¹⁵N values between shoot and nodulated root (Δδ¹⁵N_s-nr), and that between shoot and root (Δδ¹⁵N_s-r) in 6-month-old plants grown in pots with different soil moisture regimes. The relationships between Δδ¹⁵N_s-nr and the percentage of N derived from atmospheric N₂ (%Ndfa) calculated from the conventional ¹⁵N natural abundance method, and between Δδ¹⁵N_s-r and %Ndfa were analyzed in N₂-fixing legume Lespedeza cuneata and N₂-fixing non-legume Elaeagnus pungens and Myrica rubra. A close correlation was found between Δδ¹⁵N_s-nr and %Ndfa as well as between Δδ¹⁵N_s-r and %Ndfa in Lespedeza cuneata, while no correlation was found in N₂-fixing non-legume species. The results indicated that Δδ¹⁵N signatures could be useful for estimating %Ndfa for N₂-fixing perennial legume (Lespedeza cuneata) in the first growth season but might not be applicable for N₂-fixing actinorhizal plants.

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Intercropping pearl millet with cowpea is a common practice in semiarid areas. Under limited water environments, competition for soil water between intercropped plants may be strong. Furthermore, the increasing soil compaction problems, due to the use of heavy machinery, may intensify competition for limited resources, particularly in the topsoil. Two field trials were conducted to evaluate the water competition ability of intercropped pearl millet when subjected to drought and soil compaction during the 2004 Japanese summer. For this purpose plant water sources were determined by the hydrogen stable isotope (deuterium) technique. Plant water relations and biomass production were also evaluated. According to the deuterium concentration values in xylem sap, pearl millet water sources were changed by the competition with cowpea. Pearl millet was forced to rely more on recently supplied (irrigation/rainfall) water. In contrast, the water sources of cowpea were unchanged by plant competition. When plants were subjected to drought, the transpiration rate of pearl millet was reduced by 40 % of its monocropped potential by competition, but that of cowpea was not. Moreover, intercropped pearl millet, under drought and soil compaction, showed lower leaf water potential and biomass than their respective monocropped counterparts. Cowpea had a higher competitive ratio under wet, dry, and compaction treatments, while pearl millet was more competitive under loose conditions. In conclusion, under drought and soil compaction, water competition restricted the water use of intercropped pearl millet, forcing pearl millet to shift to the recently supplied water. In contrast, cowpea did not show any significant changes under these stress conditions.

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To elucidate the major physiological process to cause genotypic variation in the seedling vigor of rice, we analyzed the dry matter accumulation in the seedling for diverse cultivars distinguishing hetero- and auto-trophic growth. Four cultivars in Exp. 1 and 63 cultivars in Exp. 2 were grown in a glasshouse by hydroponics for about three weeks. In Exp. 1, heterotrophic dry weight (DW_h) was regressed against thermal time (T,°C d) by logistic functions, in which the final heterotrophic dry weight (DW_h.Max) was considered the primary determinant of heterotrophic growth rate. The increase of autotrophic dry weight (DW_a, DW_t (total DW)-DW_h) was regressed to the exponential function of T with a fairly stable parameter, relative growth rate (RGR). The variation of DW_t among cultivars and seed-sizes was well represented by combining the DW_h and DW_a models. In Exp. 2, DW_t varied among cultivars from 51 to 116 mg pl^-1. The effects of cultivar-specific parameters, DW_h.Max (final DW_h) and RGR, were evaluated by calculating the standard DW_t with the mean DW_h.Max and RGR, and then substituting one of the two cultivar-specific parameters for every cultivar. The results showed that those cultivars whose superior DW_t was attributable to DW_h.Max were limited to very large-seed cultivars. If they were excluded, the estimated effect of RGR (autotrophic process) on DW_t was evidently greater than that of DW_h.Max (heterotrophic process).

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We examined the responses of doubled-haploid lines (DHLs) of rice (Oryza sativa L.) to drought and rewatering in controlled rainfed lowland conditions, to test the the hypothesis that the DHLs would permit trait comparisons with less confounding by unrelated traits than had been reported previously. IR62266 and four DHLs derived from the cross between IR62266 and CT9993 (DHL-32, 51, 54 and 79) were grown in pot experiments in the greenhouse at the IRRI, Los Baños, Philippines. Genotypic variation in leaf and tiller development, transpiration, water use efficiency, osmotic adjustment and leaf water potential was examined in relation to dry matter production. Results revealed that greater seedling vigor through continued leaf expansion in early drought was associated with greater dry matter production after rewatering. A higher water use efficiency was related to a greater increase in dry matter production during drought. Leaf water potential was correlated strongly with dry weight, not only during drought, but especially on rewatering. Therefore, we found that the ability to continue leaf expansion, higher water use efficiency, and a greater osmotic adjustment for maintenance of leaf water potential as drought progressed were desirable traits for improved performance under drought and improved ability to recover on rewatering. These relationships could be analyzed precisely using such genetically-related materials as DHLs, with less confounding effects of plant size and genetic background.

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We investigated the tolerance to flooding in reducing conditions of five maize inbred lines and identified a quantitative trait locus (QTL) for the trait. Flooding treatment with 0.1% to 0.4% starch solution for 14 d reduced soil redox potential to about — 200 mV, mimicking reducing conditions in soil. Treatment with 0.2% starch revealed wide varietal differences in dry matter production among the five maize inbred lines. We identified the QTL for flooding tolerance in reducing conditions in a population of 178 F₂ plants derived from a cross of inbred lines F1649 (tolerant) and H84 (sensitive). Flooding tolerance, evaluated as the degree of leaf injury following treatment with 0.2% starch solution, revealed wide variation in the F₂ population. Amplified fragment length polymorphism (AFLP) markers linked to flooding tolerance gene(s) were screened with 64 AFLP primer combinations using 15 of the 178 F₂ plants from each extreme representing the ‘tolerant’ and ‘sensitive’ plants, and found 11 AFLP markers associated with flooding tolerance. Of these, 10 co-segregated and were assigned to chromosome 1. Six SSR primer pairs around these markers were used to construct a linkage map. Composite interval mapping analysis revealed that a single QTL for degree of leaf injury was located on chromosome 1 (bin 1.03-4). Another QTL for flooding tolerance, evaluated as dry matter production under flooding with 0.2% starch, was located at the same position. These results suggest the potential to increase productivity by transferring flooding tolerance genes from F1649 to elite maize inbred lines.

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