Effects of soil and atmospheric drought on whole-tree transpiration (E(T)), leaf water potential (Ψ(L)) and whole-tree hydraulic conductance (K(T)) were investigated in mature rubber trees (Hevea brasiliensis, clone RRIM 600) during the full canopy stage in the rainy season in a drought-prone area of northeast Thailand. Under well-watered soil conditions, transpiration was tightly regulated in response to high evaporative demand, i.e., above reference evapotranspiration (ET(0)) ~2.2 mm day(-1) or maximum vapor pressure deficit ~1.8 kPa. When the trees experienced intermittent soil drought E(T) decreased sharply when relative extractable water in the top soil was < 0.4. The midday leaf water potential (Ψ(md)) on sunny days did not change as a function of soil drought and remained stable at approximately - 1.95 MPa, i.e., displaying isohydric behavior. The decrease in E(T) was mainly due to the change in K(T). K(T) remained constant over a wide range of environmental conditions and decreased sharply at low soil water availability. A simple hydraulic model incorporating critical minimum water potential and the response of whole-tree hydraulic conductance to relative extractable water correctly simulated patterns of transpiration over 6 months. We conclude that an explicit and simplified framework of hydraulic limitation hypothesis was sufficient to describe water use regulation of a mature rubber tree stand in water-limited conditions. Given the complexity of constraints in the soil-plant-atmosphere pathway, our results confirm the relevance of this approach to synthesize the overall behavior of trees under drought.

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The cropping system model, namely, the crop environment resource synthesis-rice (CSM-CERES-Rice) model, is a decision supporting tool for the design of crop management. This study aimed to determine management practices for increasing rice (Oryza sativa L.) production in Laos by using the CSM-CERES-Rice model. The model was evaluated with data sets from the TDK8 and TDK11 cultivars in farmers' fields in the Vientiane plain in 2012. Anthesis and harvesting dates, growth and yield for various management scenario combinations (eight transplanting dates × two levels of plant densities × three rates of nitrogen (N) fertilizer application) for both cultivars were simulated by the model from 1980 to 2012. The model evaluation results showed strong agreement between simulated and observed data for days to harvest with a difference within four days. The model provided acceptable accuracy for grain yields with normalized root mean square error values ranging between 1 and 16 %. The results from the model application indicated that TDK8 and TDK11 produced similar yields. Transplanting TDK8 with two plant densities produced similar yields. The highest yield for both cultivars was achieved on the transplanting date of 15 Jan. N-fertilizer application at 60 and 120 kg N ha −1 was able to increase yield for TDK8 by 50 and 87 %, respectively, and for TDK11 by 54 and 70 %, respectively. Rice transplanted on 15 Jan with 5 seedlings hill −1 and N-fertilizer at 120 kg N ha −1 had the highest average yield for both cultivars with 6,460 and 6,351 kg ha −1 for TDK8 and TDK11, respectively. The CSM-CERES-Rice model is an alternative tool in determining crop management practices for rice production.

Physiological traits responsible for differences in yield performance among pre-released genotypes are normally not known. The objective of the present study was to evaluate seasonal variations in dynamic growth and development traits between 12 large-seeded Virginia-type and 14 small-seeded Spanish-type advanced breeding lines of peanut (Arachis hypogaea L.). The experiment was conducted in 1999 and 2000 at Khon Kaen University in Northeast Thailand for three planting dates, representing the early-rainy season, mid-rainy season and dry season. Very similar phenological development was observed for all lines within each group and between the early and the mid-rainy seasons. However, a lower temperature during the early growth stage in the dry season delayed flower initiation and extended maturity. During this period, crop growth rates as well as the development rate for leaf area index and specific leaf area were also lower compared with the rainy seasons. On average, both pod yield and total biomass for the rainy season and the dry season were about the same. Variations among lines within each group were also small. For these advanced breeding lines, the pod growth rate was the most important yield determinant while the crop growth rate had lesser effect and the partitioning coefficient and pod-filling duration had no significant effect. However, the crop growth rate, pod growth rate and partitioning coefficient were important traits for a line to be the top yielder. Pod-filling duration was also important when the lines involved were considerably diverse in maturity and seed size. Information on these traits, if used together with final pod yield, will make varietal selection more efficient.