Estimation of Soil and Crop Hydraulic Properties

Some two dozen methods for estimating infiltration and roughness parameters from field measurements of test irrigations are reviewed in this paper. They differ in their assumptions, ease of analysis, quantity of field data required, and accuracy. They are divided into two broad categories, depending upon the basic approach to determine infiltration. One features direct application of mass conservation, expressed in terms of the infiltration parameters and then inverted in some way in order to extract those parameters. The other involves repeated simulation with a sequence of values of the infiltration parameters, coupled to some kind of search procedure—an optimization—to minimize differences between simulation and measurement. A new one-point technique is proposed, along with suggestions for extending existing methods.     

试论转基因主粮产业安全与风险

Genetically modified (GM) crops may bring out serious environmental disruption and potential food safety problems which has already gone beyond the scientific and technological scope. Various business interest groups, especially GM multinationals, achieve the purpose of controlling another country's food lifeline through the monopoly of intellectual property rights of genetically modified seeds. On the basis of commercial cultivation of GM crops in national food security, food safety, health risks, environmental security, social risk and so on, this article briefly introduces the progress of the study at home and abroad, and puts forward measures to address national food security from the ecological point of view. China has the advantages of traditional ecological cycle in agriculture by adopting the theory of restoration ecology. This would be a desirable way.     

~(226)Ra在土壤-农作物系统中的积累和转移

本文根据1979—1981年在铀尾矿坝附近田间试验的数据,探索了~(226)Ra 在土壤-农作物系统中积累和转移的某些规律。试验得出;土壤中~(226)Ra 含量 X 和转移系数 Y 之间的关系,可用下列幂函数来描述:y=0.0045x~(-0.61766)(对蔬菜而言)y′=0.0012x′~(-0.27103)(对稻米而言)在镭的陆地生态系统转移中,气载~(226)Ra 直接污染农作物种子的作用不大。     

ReSET-Raster: Surface Energy Balance Model for Calculating Evapotranspiration Using a Raster Approach

Surface energy balance models developed for mapping evapotranspiration at high resolution use weather station data. Previous models such as SEBAL or METRIC use wind and reference evapotranspiration from a single weather station. A third model (ReSET) uses wind run from multiple weather stations but uses a single weather station for the internal calibration. Because these models solve the energy balance equation for areas that usually have significant spatial variability, it is more appropriate to have all inputs and calculations in a raster format. This paper presents a full rasterized model, which uses all inputs and performs all calculations in a raster format (ReSET-Raster). The ReSET-Raster model provides the flexibility to use several weather stations as data sources to generate interpolated weather parameters in a raster format. It explicitly takes into account the spatial variation of weather parameters between weather stations, which can be significant. This paper presents examples showing that evapotranspiration calculated with the raster approach can vary as much as 17% compared with evapotranspiration calculated with point values.     

INFLUENCE OF PROCESS CONDITIONS ON THE DRYING RATE OF CASSAVA CHIPS IN A SOLAR SIMULATOR

ABSTRACT

Experiments were carried out in a solar simulator to study the influence of air temperature (25-40°C), air relative humidity (40-80%), air velocity (0.95-2.2 m/s), radiation intensity (0-916 W/m²), and loading density (10-30 kg/m²) on the drying rate of a bed of cassava chips (2×2×2 cm). Well-known thin-layer drying equations were fitted to the experimental data, and the empirical constants were used in a statistical analysis of the influence of process conditions on the drying rate. The air temperature, air velocity, radiation intensity, and loading density influenced the drying rate significantly (p=0.05). The effects of the air temperature and the radiation intensity were attributed to the temperature-dependent diffusion of moisture within the chips, while the effect of the air velocity was ascribed to the resistance to mass transfer at the air-chip interface. Equations were presented to express the empirical constants as functions of the process variables.     

Cropland Measurement Using Thematic Mapper Data and Radiometric Model

To halt erosion and desertification, it is necessary to quantify resources that are affected. Necessary information includes inventory of croplands and desert areas as they change over time. Several studies indicate the value of remote sensor data as input to inventories. In this study, the radiometric modeling of spectral characteristics of soil and vegetation provides the theoretical basis for the remote sensing approach. Use of Landsat Thematic Mapper images allows measurement of croplands in Saudi Arabia, demonstrating the capability of the approach. The inventory techniques and remote sensing approach presented are potentially useful in developing countries.     

New Weighing Method to Measure Shoot Water Interception

The need exists to develop a method that can quantitatively measure water interception from plant shoots. This paper describes a new method for measuring canopy water interception. Corn (Zea Mays L.) was grown in 13?L buckets containing Valentine fine sand (Mixed, mesic Typic Ustipsamment) under a climate-controlled growth chamber. Plants were taken out of the growth chamber for 2–3?h periods for measurements of shoot water interception in a hydraulic laboratory equipped with an Accupulse system suspended from the ceiling that was used to wet the corn shoots at growth stages V7–V13. A lightweight, movable framework was placed around a balance, and buckets containing corn plants were placed on the scale one container at a time. Water was applied until all shoot surfaces were wet and runoff from the leaves and stalk surfaces could be observed. The weighing method for shoot water interception was tested by using the balance to instantaneously measure shoot water interception during application of water and after plant surface runoff ceased. The balance, bucket, and soil surface were covered with plastic to protect them from water, so only the shoots were wet. Interception by the shoot of corn ranged from 31?to?47?mL?shoot?1. These values were much smaller than previous values reported in the literature. The average coefficient of variation was 9.2% for two studies, which was much lower than previously accepted methods. This study suggests that the weighing method for shoot water interception can be used to quantitatively and more accurately measure water intercepted by corn shoots. The weighing intercepted method values presented in this paper are low and suggest that previous interception methods overestimated the interception values.     

Use of Alternative Temperature Expressions with Blaney-Criddle

The widely used Penman-Monteith equation to estimate crop evapotranspiration (ET) has limited utility in many areas of the world because of its requirement for full meteorological data. Legal and engineering water agencies commonly use the original Blaney-Criddle method in their efforts to manage competing water demands in mountain basins, both for its longtime familiarity and minimal data requirements. The original Blaney-Criddle equation predicts crop ET based solely on readily available mean monthly air temperature, t, and percentage of daylight hours. However, in semiarid, high-elevation environments, Blaney-Criddle underestimates crop ET. Subsequent modifications have not fully corrected this underestimation. Low nighttime temperatures at high elevations incorrectly weight the estimate, resulting in significant variation between computed crop ET and lysimeter measurements. Our objective was to evaluate three modifications of the Blaney-Criddle temperature expression against the original equation with mean t, and another temperature method, Hargreaves, using lysimeter measurements from nine irrigated grass meadow sites in the upper Gunnison River basin of Colorado (1999–2003). Two of the modified temperature expressions resulted in improved correlation of Blaney-Criddle estimated crop ET with lysimeter ET. Similar improvements were observed when estimating with Hargreaves, which incorporates an additional term, Tdiff, the difference between maximum and minimum daily temperature. Correlations of solar radiation (Rs, the primary energy input to ET) with alternative temperature expressions and Tdiff were improved over correlations of Rs with mean t, supporting the improved prediction performance of alternative temperature expressions. These modifications to the original Blaney-Criddle can be applied successfully throughout Colorado mountain basins and may be globally applicable to high-elevation areas.     

Optimal Crop Planning and Conjunctive Use of Surface Water and Groundwater Resources Using Fuzzy Dynamic Programming

Optimal crop planning and the conjunctive use of surface water and groundwater resources are imperative for the sustainable management of water resources, especially in semiarid regions. In recent years, considerable attention has been given to crop planning and water resources management under uncertainties caused by climate changes that affect irrigation planning in terms of decisions to determine the amounts of water that can/must be allocated. In this paper, optimal crop planning and conjunctive use of surface water and groundwater are developed for the Najafabad Plain, a part of the Zayandehrood River basin in west-central Iran. The fuzzy inference system (FIS) is used to account for the experience and expert judgments of decision makers and farmers to obtain optimal crop planning and cultivation with a reliable water demand based on climate conditions. In the present work, fuzzy regression is used for considering uncertainty and ambiguity in the data used in the simulation model as well as the uncertainties in interactions between surface water and groundwater. The objective function of the optimization model is to minimize shortages in supplying irrigation demands. The results are applicable to a wide range of climate conditions.     

Evapotranspiration of Full-, Deficit-Irrigated, and Dryland Cotton on the Northern Texas High Plains

Cotton (Gossypium hirsutum L.) is beginning to be produced on the Northern Texas High Plains as a lower water-requiring crop while producing an acceptable profit. Cotton is a warm season, perennial species produced like an annual yet it requires a delicate balance of water and water deficit controls to most effectively produce high yields in this thermally limited environment. This study measured the water use of cotton in fully irrigated, deficiently irrigated, and dryland regimes in a Northern Texas High Plains environment using precision weighing lysimeters in 2000 and 2001. A lateral-move sprinkler system was used to irrigate the fields. The water use data were used to develop crop coefficient data and compared with the FAO-56 method for estimating crop water use. Cotton yield, water use, and water use efficiency was found to be as good in this region as other more noted cotton regions. FAO-56 evapotranspiration prediction procedures performed better for the more fully irrigated treatments in this environment.