Estimation of supplementary water to paddy fields in the lower Mekong River basin during the dry season

Efficient management of water resources in paddy fields requires an understanding of the volume of supplementary water used. However, quantifying the volume is laborious due to the large amount of data that must be collected and analyzed. The purpose of our study was to estimate the volume of supplementary water used in paddy fields, based on several years of available statistical data, and to provide information on how much water can be supplied to paddy fields in each target area. In this study, the lower Mekong River basin of northeast Thailand, Laos, and Cambodia was selected as the study area. In the first step, we used agricultural statistics for each country, rainfall data acquired from the Mekong River Commission Secretariat (MRCS), and the value of virtual water required per unit of rice production. Because several years of data were used for dry season harvested areas and rice production in each country, the supplementary water to paddy fields in each province was calculated using virtual water and rainfall. This method made it possible to estimate changes in supplementary water in each province. Through this study, the supplementary water to paddy fields during the dry season in three countries was approximated from the minimum number of data sets. Moreover, for cases in which it is not possible to procure agricultural water use data for a hydrological model simulation, an alternative solution is proposed.     

An index for evaluating the flood-prevention function of paddies

Urbanization is expanding in and around small to medium-sized cities as well as in large cities, and the expansion includes low-lying areas where the flood risk is high. Flood risk in small watersheds has been evaluated using precise mathematical models. However, these models cannot be applied to larger basins due to the complexity of data collection and analysis. As a result, quantitative evaluations of flood risk at macro scales and the flood-prevention function of paddies around urban areas have not been made. This paper proposes a method and an index that can be used to evaluate the flood-prevention function of paddies on a regional scale. In addition, the use of this system for basin-wide management is illustrated by an example for the Kinu and Kokai rivers, which are tributaries of the Tone River of Japan. The applicability of the approach is evaluated using data from a major flood that occurred in the study area.     

Development of an innovative conceptual model and a tiered testing strategy for the ecological risk assessment of rice pesticides

Rice paddies constitute a very special agrobiosystem, which for some circumstances, could be considered as a human driven wetland. The complexity of such dynamic systems is a key element for conducting ecological risk assessments, in addition, the proximity of rice paddies to areas of high ecological value must be considered. This paper presents a new conceptual model for conducting ecological risk assessments of pesticides and other agrochemicals in rice, based on a combination of three main elements, the source of the stressor, the exposed environmental compartments and the relevance of the ecological receptors. A tiered testing strategy, starting with the standard requirements for pesticides and moving to specific higher tier studies with three levels of risk refinement is also presented.     

网络化水稻生产专家系统知识库的构建

农业专家系统是基于丰富的农业专家知识,并能模仿农业专家进行推理决策的智能计算机程序系统.知识库是农业专家系统的核心组成部分,是决定专家系统性能的关键.介绍了采用"Web浏览器/Web服务器/数据库系统"分布式计算体系结构的水稻生产专家系统的结构、功能和特点,详细论述了运用加权模糊产生式规则表示本领域专家们的知识和经验,构建水稻生产系统知识库的理论与方法.     

Comparison of sulfurous acid generator and alternate amendments to improve the quality of saline-sodic water for sustainable rice yields

The prolonged irrigation with marginal quality water can cause secondary salinization of soils, which necessitates for better understanding of water management alternatives. Relative performance of sulfuric acid and gypsum is still controversial to counter sodium hazards in soil/water system. As an alternative, sulfurous acid generators (SAG) are also being marketed. But up-till-now, there is not even a single field study published in scientific journals about their efficiency and economical viability for the treatment of saline-sodic water. Therefore, a field study was carried out to compare the effectiveness of SAG and alternate amendments applied on an equivalent basis to grow rice crop. SAG treatment of saline-sodic tube well water decreased only residual sodium carbonate (RSC) from 5.4 to 3.6 mmol_c l⁻¹, and had no beneficial effect on its sodium adsorption ratio (SAR) or electrical conductivity (EC). All the treatments kept soil EC and SAR around their respective threshold levels. For paddy yield, SAG, sulfuric acid, and gypsum treatments depicted nonsignificant differences. SAG and sulfuric acid treatments of water were about six times expensive than that of gypsum. It was concluded that soil-applied gypsum, to counter sodic hazards of irrigation water, is economical to sustain irrigated rice in dry regions.     

A water balance model for characterization of length of growing period and water stress development for rainfed lowland rice

There is large year-to-year variation in rice production across the Mekong region (Laos, Cambodia and Thailand) due to uncertainty in the timing of the onset of the wet season and drought stress that may develop at any time during the growth of rainfed lowland rice. Unique to the nature of lowland water balance is a large component of deep percolation water loss, which depends on soil texture. The objectives of this study were to develop a soil water balance model for calculating the amount of water held in field storage (i.e. in soil and, if there is standing water, above the soil surface) and to apply it to determine the length of growing period (LGP) and water stress development in relation to soil type and rainfall pattern for the rice ecosystem. The water balance is computed separately for above-ground plus topsoil layer and subsoil layer. Components of the water balance are the existing amount of stored water, rainfall, evapotranspiration, deep percolation, and runoff. The deep percolation rate was determined from clay content in each soil layer. The model runs with daily or weekly weather data to estimate the soil water level for the growing period in the wet season. The model was validated with data collected from top, middle and bottom of rainfed lowland fields in Savannakhet province, Laos. The best correlation between the observed and simulated water level was obtained (r² = 0.41) for middle fields. The simulation results showed that LGP varied greatly from year to year, particularly in locations with sandy soils, due mostly to variation in monthly rainfall occurring at the early part of the growing season (April), but also to some extent by variation at the end of growing season (October). Soil texture on the other hand is shown to have a large influence on the end of the rice growing period and hence LGP, and also water stress development during growth. Sandy soils with clay content less than 7% that are prevalent in the province are shown to cause frequent water stress and early finish in rainfed lowland rice. The model accordingly provides reasonable outputs that can provide a geographical dimension of soil hydrological patterns for various rice growing environments, and also identify the spatial pattern of drought stress that is likely to occur. Model outputs can be used to provide guidelines for practical advice to the rice farmers and researchers for determination of appropriate crop management strategies (e.g. time of planting, varieties), and policy makers for investment decisions on inputs (e.g. fertilizer price) aimed at increasing rice productivity in this Mekong region.     

A model driven by crop water use and nitrogen supply for simulating changes in the regional yield of rain-fed lowland rice in Northeast Thailand

Climate change will have significant impacts on the rain-fed rice production ecosystem, and particularly on the ecosystem’s hydrology and water resources. Under rain-fed lowland conditions, substantial variations among fields in grain yield are commonly observed, but a method that can account for field-scale yield variability to produce regional-scale yield estimates is lacking, thereby limiting our ability to predict future rice production under changing climate and variable water resources. In this study, we developed a model for estimating regional yields of rain-fed lowland rice in Northeast Thailand, by combining a simple crop model with a crop calendar model. The crop model incorporates the effects of two important resources (water and nitrogen) on crop growth. The biomass accumulation is driven by water use, whereas the nitrogen supply determines canopy development and thereby constrains crop water use. Accounting for the wide range of planting dates and the strong photoperiod-sensitive characteristics of rice varieties through the calendar model is an essential component in determining regional yield estimates. The present model does not account for the effects of mid-season drought or flooding, but was nonetheless able to explain the spatial and temporal yield variations at the province level for the past 25 years. Thus, it can be used as a prototype for simulating regional yields of rain-fed lowland rice.     

Genetic relationship between grain yield and the contents of protein and fat in a recombinant inbred population of rice

To study the genetic relationship between grain yield and the nutrient contents in rice, 209 recombinant inbred lines derived from a cross between indica rice Xieqingzao B and Milyang 46 were used to determine quantitative trait loci (QTLs) affecting the yields and contents of the two major nutritional components in brown rice. Seven traits were analyzed, including brown rice recovery (BRR), protein content (PC), fat content (FC), grain yield (GYD), brown rice yield (BRYD), protein yield (PYD) and fat yield (FYD). The nutrient contents were significantly negatively correlated with BRR, GYD and BRYD, and the variations on nutrient yield were mainly ascribed to GYD. A total of 22 QTLs distributed on 10 regions of eight chromosomes were detected. Two QTL clusters were found on the short arm of chromosome 6 and the long arm of chromosome 10, respectively. The former was responsible for all the seven traits, and the latter for all the traits except BRR and FC. In both regions, the maternal alleles decreased nutrient contents, but they increased the yields of grain, brown rice, protein and fat. Implication of these results for the breeding of rice varieties with enhancing nutritional capacity is discussed.