Elevation and infiltration in a level basin. II. Impact on soil water and corn yield

The spatial variability of irrigation water recharge and crop yield is affected by a number of factors. Soil surface elevation, infiltration and soil water MAD are the most relevant related to level-basin irrigation. Measurements of soil water recharge (using a neutron probe) were compared to estimates based on ring infiltrometers and observations of the opportunity time. Estimates of cumulative infiltration (ECI) were obtained, separating the variability of infiltration and opportunity time (largely determined by elevation). Soil surface elevation was correlated with measured recharge, grain yield and total dry matter. A correlation was found between infiltration and the measurements of water recharge. While soil surface elevation can be regarded as a management variable, little can be done to reduce the variability of infiltration. Distribution uniformities from ECI were about 20% higher than those obtained from measurements of water recharge. Seasonal uniformity was only marginally higher than average uniformity, confirming the low random component of water recharge in level-basin irrigation. Deep percolation was more intense in areas with low MAD. This finding emphasizes the relevance of characterizing the variability of soil physical properties in surface irrigation. Extrapolation of the results of this research to field-scale irrigation basins should take into account the methodology used: in particular, the reduced scale of the experimental level basin. Received: 24 February 1998     

Assessment of irrigation and environmental quality at the hydrological basin level: I. Irrigation quality

Irrigated agriculture notably increases crop productivity, but consumes high volumes of water and may induce off-site pollution of receiving water bodies. The objectives of this paper were to diagnose the quality of irrigation and to prescribe recommendations aimed at improving irrigation management and reducing the off-site pollution from a 15,500 ha irrigation district located in the Ebro River Basin (Spain). Three hydrological basins were selected within the district where the main inputs (irrigation, precipitation, and groundwater inflows) and outputs (actual crop's evapotranspiration, surface drainage outflows, and groundwater outflows) of water were measured or estimated during a hydrological year. The highest volume of water (I = 1400 mm/year) was applied in the basin with highly permeable, low water retention, flood irrigated soils where 81% of the total surface was planted with alfalfa and corn. This basin had the lowest consumptive water use efficiency (CWUE = 45%), the highest water deficit (WD = 5%) and the highest drainage fraction (DF = 57%). In contrast, the lowest I (950 mm/year), the highest CWUE (62%), and the lowest WD (2%) and DF (37%) were obtained in the basin with 60% of the surface covered with deep, high water retention, alluvial valley soils, where 39% of the cultivated surface is sprinkler irrigated and with only 48% of the surface planted with alfalfa and corn. We concluded that the three most important variables determining the quality of irrigation and the volume of irrigation return flows in the studied basins were (i) soil characteristics, (ii) irrigation management and irrigation system, and (iii) crop water requirements. Therefore, the critical recommendations for improving the quality of irrigation are to (i) increase the efficiency of flood-irrigation, (ii) change to pressurized systems in the shallow and highly permeable soils, and (iii) reuse of drainage water for irrigation within the district. These management strategies will conserve water of high quality in the main reservoir and will decrease the crop water deficits and the volume of irrigation return flows, therefore, minimizing the off-site pollution from this irrigation district.     

Intra-annual variability in the contribution of tile drains to basin discharge and phosphorus export in a first-order agricultural catchment

This study examines spatiotemporal variability (event-based, seasonal) in the contribution of drainage tiles within a basin to basin hydrologic discharge and soluble reactive phosphorus (SRP) and total phosphorus (TP) export over a period of 1 year. Tile discharge was highly variable at both moderate (wet versus dry periods) and smaller (within-event) temporal scales, accounting for 0-90% of basin discharge at any given time. An estimated 42% of basin annual discharge originated from drainage tiles, the majority of which occurred during the winter and spring months. Concentrations of SRP and TP in drainage tile effluent were also highly variable in space and time (1-2850 μg SRP L⁻¹, 5-8275 μg TP L⁻¹). Higher concentrations of SRP and TP were linked to fields receiving manure compared to fields receiving inorganic fertilizers. SRP export from tiles accounted for 118% of basin SRP export on average, although their contribution to basin SRP export ranged from 4 to 344% on 32 discrete dates during which all tiles in the basin were sampled for hydrochemistry. On the same 32 dates, tiles accounted for an average of 43% of basin TP export, although this ranged from 0 to 200%. Management options such as tile plugs and optimizing the timing and application rates of fertilizer should be explored to minimize nutrient export from tiles.     

Spatial variability of solutes in a pecan orchard surface-irrigated with untreated effluents in the upper Rio Grande River basin

Untreated effluents are blended with water from the Rio Grande River and used for irrigation in the Juarez Valley of northern Mexico. Effluents are a source of nutrients, but may also be a source of heavy metal contamination. This study was conducted to characterize deposition patterns of selected metals, salts, and total nitrogen in a 6 ha pecan (Carya illinoenisis K.) orchard which had healthy-to-stunted trees with dieback. Orchard soil was collected along multiple transects to depths of 1.2 m, with spacing every 20 m. All solutes showed a magnitude variability in particular ions. Chromium, Ni, Pb, and Cd concentrations averaged <14 mg kg⁻¹. Soil Na, Ca, K, Mg, SO₄, Cl and NO₃–N averaged <100 mg kg⁻¹. Total N was <0.21%. Most solutes accumulated at the soil surface with the exception of Na and SO₄. Linear semi-variograms best described spatial metal deposition and surface clay content with a range of influence >189 m. Spherical semi-variograms best described spatial distribution of salts and total N, but accounted <50% of the variability. The solubility of solutes in moderately alkaline irrigation water and their specific behavior in calcareous soils likely affected deposition patterns. Estimated metal loads from irrigation over a 15-year period were <3 kg ha⁻¹, but about 187 Mg ha⁻¹ for total dissolved solids (salts). Pecan leaf tissue showed no signs of heavy metal accumulation. Suboptimum pecan growth was associated with salt accumulation in a clayey area with low permeability. Salts, in particular Na, rather than metals may be the most important inorganic contaminants for irrigated agriculture in this region. Salt loads in irrigation waters are expected to increase as agriculture increasingly relies on urban effluents too expensive to convert to potable water.     

Spatial variability of heavy metals in irrigated alfalfa fields in the upper Rio Grande River basin

Reduced quality of wastewater discharged into the Rio Grande River is reported to be the cause of crop contamination and heavy metal transport onto fertile soils. This study was conducted to characterize Cd, Pb, Ni, Zn, Cr, and Co concentrations in two alfalfa (Medicago saliva L.) fields irrigated with river water (in Texas) or wastewater mixed with river water (in Mexico) and to examine spatial variability of acid-extractable metal deposition in soil and in uptake by alfalfa. Multiple transects were established in both fields for intensive forage collection and soil sampling to depths of 1.2 m, with spacing every 7.6 or 15.2 m. Metal concentrations rarely exceeded 20 mg kg⁻¹ with the exception of Zn. Relative metal concentrations were in the order Zn > Cr > Ni > Pb > Co > Cd in both fields, and were highly correlated with clay content within the plow zone. Linear and spherical variogram models best described surface metal deposition with spatial dependence > 100 m with regard to irrigation delivery. However, increasing metal concentrations below the plow zone at the Texas site, inconsistent geostatistical trends for soil Zn and Ni, and no association of Pb with soil texture suggested that irrigation delivery was not the exclusive transport source. Estimated metal loads from river water over a 50-year period suggested that irrigation may account for up to 31 % of surface metals. It is likely that atmospheric fallout from a local ore smelter and indigenous background levels significantly contributed to observed soil metal levels. Metal concentrations in unwashed alfalfa forage tissue were at least five times less than those in soil and showed no consistent association with soil concentrations. Metal concentrations in alfalfa forage posed no toxicity threat to animals or public health. Blending wastewaters in the Rio Grande River and canal system has diluted heavy metals to low concentrations for irrigation, but not to more stringent levels for fish and wildlife. Degraded waters could be diverted from the river and directly used for irrigation under careful water and soil management.     

Assessment of irrigation and environmental quality at the hydrological basin level: II. Salt and nitrate loads in irrigation return flows

Irrigation return flows may induce salt and nitrate pollution of receiving water bodies. The objectives of this study were to perform a salt and nitrogen mass balance at the hydrological basin level and to quantify the salt and nitrate loads exported in the drainage waters of three basins located in a 15,500 ha irrigation district of the Ebro River Basin (Spain). The main salt and nitrogen inputs and outputs were measured or estimated in these basins along the 2001 hydrological year. Groundwater inflows in the three basins and groundwater outflow in one basin were significant components of the measured mass balances. Thus, the off-site impact ascribed solely to irrigation in these basins was estimated in the soil drainage water. Salt concentrations in soil drainage were low (TDS of around 400–700 mg/l, depending on basins) due to the low TDS of irrigation water and the low presence of salts in the geologic materials, and were inversely related to the drainage fractions (DF = 37–57%). However, due to these high DF, salt loads in soil drainage were relatively high (between 3.4 and 4.7 Mg/ha), although moderate compared to other areas with more saline geological materials. Nitrate concentrations and nitrogen loads in soil drainage were highest (77 mg NO₃⁻/l and 195 kg N/ha) in basin III, heavily fertilized (357 kg N/ha), with the highest percentage of corn and with shallow, low water retention flood-irrigated soils. In contrast, the lowest nitrate concentrations and nitrogen loads (21 mg NO₃⁻/l and 23 kg N/ha) were found in basin II, fertilized with 203 kg N/ha and preponderant in deep, alluvial valley soils, crops with low N requirements (alfalfa and pasture), the highest non-cropped area (26% of total) and with fertigation practices in the sprinkler-irrigated fields (36% of the irrigated area). Thus, 56% of the N applied by fertilization was lost in soil drainage in basin III, as compared to only 16% in basin II. In summary, a low irrigation efficiency coupled to an inadequate management of nitrogen fertilization are responsible for the low-salt, high-nitrate concentrations in soil and surface drainage outflows from the studied basins. In consequence, higher irrigation efficiencies, optimized nitrogen fertilization and the reuse for irrigation of the low-salt, high-nitrate drainage waters are key management strategies for a better control of the off-site pollution from the studied irrigation district.     

Climate variability during the past 2,000 years and past economic and irrigation activities in the Aral Sea basin

The lake level history, here based on the relative abundance of Ca (gypsum), is used for tracing past hydrological conditions in Central Asia. Lake level was close to a minimum before approximately a.d. 300, at about a.d. 600, a.d. 1220, a.d. 1400 and since 1960s it is lowering again. Lake water level was lowest during the fourteenth or early fifteenth centuries as indicated by a coeval settlement, which today is still under water near the well-dated mausoleum of Kerderi. Pollen data from riparian vegetation indicate generally wet conditions between a.d. 400 and a.d. 900, intermitted by short intervals with drier conditions (AD 550–600; a.d. 650–700) and riverbanks were again dry from a.d. 900–1150, a.d. 1450–1550, and from a.d. 1970 onward moisture decreased steadily. Irrigation activities were at a maximum between 300 b.c. and a.d. 300 (Classical Antiquity) and between a.d. 800 and a.d. 1300 (Medieval Age) and after a.d. 1960.     

Impacts of climate variability on reference evapotranspiration over 58 years in the Haihe river basin of north China

Physically, evaporative demand is driven by net radiation (R_n), vapour pressure (e_a), wind speed (u₂), and air temperature (T_a), each of which changes over time. By analyzing temporal variations in reference evapotranspiration (ET₀), improved understanding of the impacts of climate change on hydrological processes can be obtained. In this study, variations in ET₀ over 58 years (1950-2007) at 34 stations in the Haihe river basin of China were analyzed. ET₀ was calculated by the FAO Penman-Monteith formula. Calculation of Kendall rank coefficient was done by analyzing the annual and seasonal trends in ET₀ derived from its dependent climate variables. Inverse distance weighting (IDW) was used to analyze the spatial variation in annual and seasonal ET₀, and in each climate variable. An attribution analysis was performed to quantify the contribution of each input variable to ET₀ variation. The results showed that ET₀ gradually decreased in the whole basin over the 58 years at a rate of −1.0 mm yr⁻², at the same time, R_n, u₂ and precipitation also decreased. Changes in ET₀ were attributed to the variations in net radiation (−0.9 mm yr⁻²), vapour pressure (−0.5 mm yr⁻²), wind speed (−1.3 mm yr⁻²) and air temperature (1.7 mm yr⁻²). Looking at all data on a month by month basis, we found that T_a had a positive effect on dET₀/dt (the derivative of reference evapotranspiration to time) and R_n and u₂ had negative effects on dET₀/dt. While changes in air temperature were found to produce a large increase in dET₀/dt, changes in other key variables each reduced rates, resulting in an overall negative trend in dET₀/dt.     

Pangani River Basin over time and space: On the interface of local and basin level responses

As the pressure on the water resources mounts within a river basin, institutional innovation may occur not as a result of a planned sequence of adjustments, but arising out of the interplay of several factors. By focusing on the basin trajectory this paper illustrates the importance of understanding how local-level institutional arrangements interface with national-level policies and basin-wide institutions. We expand Molle's typology of basin actors responses by explicitly introducing a meso-layer which depicts the interface where State-level and local-level initiatives and responses are played out; and focus on how this interaction finds expression in the creation and modification of hydraulic property rights. We subsequently apply this perspective to the case of Pangani River Basin in Tanzania.The Pangani River Basin development trajectory did not follow a linear path and sequence of responses. Attempts by the state government to establish ‘order’ in the basin by issuing water rights, levying water fees and designing a new basin institutional set-up have so far proven problematic, and instead generated ‘noise’ at the interface.So far water resources development in the Pangani has primarily focused on blue water, and the paper shows how investments in infrastructure to control blue water have shaped the relationship between water users, and between water user groups and the State. It remains unknown, however, what the implications will be of widespread investments in improved green water use throughout the basin - not only hydrologically for the availability of blue water, but also socially for the livelihoods of the basin population, and for the evolving relationships between green and blue water users, and between them and the State. The paper concludes with a question: will green water development engender a similar double-edged material-symbolic dynamic as blue water development has.The findings of this paper demonstrate that the expanded typology of basin actors’ responses helps to better understand the present situation. Such an improved understanding is useful in analysing current and proposed interventions.     

Impact of a gel conditioner and water quality upon soil infiltration

Summary The interactive effects of 0.0%, 0.4%, and 0.8% of a gel conditioner, Jalma, and four waters: salt solution (SS), distilled (DW), natural sewage (SW), and well (WW) waters on swelling (S), effective mean pore radius ( ), water penetrability (), diffusivity (D), and weighted-mean diffusivity ( ) in loamy sand and loam soil columns were investigated. The diffusivities of water in untreated soil columns were nearly independent of water quality. In general for both soils, S decreased, and , , and increased with increase in water salinity and decrease in % Jalma. For the loamy sand of SS, WW, SW, and DW were reduced, respectively by 15%, 39%, 45%, and 55% due to the addition of 0.4% Jalma and by 15%, 52%, 69%, and 83% due to addition of 0.8% Jalma compared to untreated control. It was concluded that 0.4% Jalma is the optimum rate when sewage (EC=1.6 dSm^–1) or other waters of low salinity are used for irrigation and 0.8% Jalma when well water (EC =6.4 dSm^–1) is used. When the irrigation water is of high salinity (EC =42.5 dSm^–1), use of this gel conditioner is not recommended. Effective mean pore radius proved to be a reliable predictor of the multiple effects of texture, Jalma and water salinity on and .     

Livestock water productivity in mixed crop–livestock farming systems of the Blue Nile basin: Assessing variability and prospects for improvement

Water scarcity is a major factor limiting food production. Improving Livestock Water Productivity (LWP) is one of the approaches to address those problems. LWP is defined as the ratio of livestock’s beneficial outputs and services to water depleted in their production. Increasing LWP can help achieve more production per unit of water depleted. In this study we assess the spatial variability of LWP in three farming systems (rice-based, millet-based and barley-based) of the Gumera watershed in the highlands of the Blue Nile basin, Ethiopia. We collected data on land use, livestock management and climatic variables using focused group discussions, field observation and secondary data. We estimated the water depleted by evapotranspiration (ET) and beneficial animal products and services and then calculated LWP. Our results suggest that LWP is comparable with crop water productivity at watershed scales. Variability of LWP across farming systems of the Gumera watershed was apparent and this can be explained by farmers’ livelihood strategies and prevailing biophysical conditions. In view of the results there are opportunities to improve LWP: improved feed sourcing, enhancing livestock productivity and multiple livestock use strategies can help make animal production more water productive. Attempts to improve agricultural water productivity, at system scale, must recognize differences among systems and optimize resources use by system components.     

Crop coefficient of sesame in a semi-arid region of I.R. Iran

Crop coefficient of sesame is necessary for the water requirement estimation in irrigation water planning and management. This study has been initiated to determine the crop coefficient (K_c) of sesame in a semi-arid climate. The relationships between K_c and ET_p/E_p (pan evaporation) and leaf area index (LAI), growing degree-day (GDD) and days after sowing (DAS), were also investigated. The seasonal ET_p for sesame in the study area with a 5 month growth period was 910 m. The mid-season and late-season K_c values for sesame were 1.08 and 0.64, respectively. These values are somewhat lower and higher than those for other oil seed crops. The K_c value for the initial stage was close to that obtained by the procedure proposed by Allen et al. [Allen, R.G., Smith, M., Pereira, L.S., Pruitt, W.O., 1997. Proposed revision to the FAO procedure for estimating evapotranspiration. In: The Second Iranian Congress on Soil and Water Issues, 15–17 February 1997. Tehran, I.R. of Iran, pp. 1–18]. The ratio of ET_p/E_p varied between 0.49–1.0 from the beginning to the middle of the growing season which is a sign of mild local advection in the region. The maximum ratios of ET_p/ET₀ and ET_p/E_p occurred at a LAI of 3.0. Furthermore, third-order polynomials were presented to predict the K_c values from days after sowing (DAS), percent days after sowing (%DAS) and growing degree-day (GDD).     

Spatial variability of rainfall and yield of maize in a semiarid region

The influence of nonuniform rainfall distribution patterns on the variability of maize yield and soil water use was studied with the aid of the analyses of rainfall and evapotranspiration data of a semiarid region. The analyses enabled us to define homogeneous areas of soil water availability through the application of a geostatistic algorithm developed for the computation of semivariograms, autocorrelograms and crosscorrelation functions.Water economy and yield of nonirrigated maize grown at each homogeneous area is evaluated through the application of a modification of Hanks' yield—evapotranspiration model.To optimize rainfall use by the crop under semiarid conditions, the effect of differences in soil water availability and maize varietal responses to water stress are evaluated. Results indicate that, when these differences are considered in the selection of maize cultivars, a significant increment in total regional production can be expected.     

Estimation of the infiltration rate of a paddy field in Yun-Lin,Taiwan

Flooded paddy fields perform many functions, including not only rice production, but also ecological and environmental conservation, since the paddy field is periodically flooded and thus becomes a major source of ground water recharge. This work estimates the extent of infiltration in a paddy field in Yun-Lin, Taiwan by adopting a one-dimensional Darcy-based soil/water balance model SAWAH (Simulation Algorithm for Water Flow in Aquatic Habitats) and two sets of empirical equations used by the Taiwan Provincial Water Conservancy Bureau. A 7.5-cm thick plow sole layer with a hydraulic conductivity of 0.03–0.055 cm/day, coupled with the irrigation data obtained from the Ma-Yan station in Yun-Lin is selected to estimate the volumetric amount of annual infiltration in the study region. Simulation results from SAWAH indicate that the plow sole layer controls the movement of infiltrated water, with a rate ranging from 0.2167 to 0.2248 billion cubic meters annually. The infiltration rate estimated from empirical equations ranges from 0.337 to 0.3891 billion cubic meters per year, twice as high as that obtained from SAWAH. This finding suggests that the empirical equations designed to estimate the amount of irrigation water required for rice growth in the paddy may over-estimate infiltration rates. The simulated annual infiltration rate can be combined with the Geographical Information System to delineate the potential recharge zone for ground water management in Yun-Lin, Taiwan.     

影响直喷式柴油机挤流特征的几个因素

对3种不同结构燃烧室所对应的缸内流场进行了模拟研究，系统地分析了挤流的演变过程和柴油机转速、燃烧室结构、进气涡流对其特征的影响。在上止点前或后较大的曲轴转角范围内流场相似，逆挤流叠加于由气体惯性作用保持的环涡之上并集中于燃烧室边缘，燃烧室内速度和湍流度随柴油机转速和燃烧室缩口度同向变化。进气涡流是湍流生成的主要因素并使流场复杂化，随涡流和挤流相对强弱的变化，燃烧室内形成的环涡的个数、转向和强度不同。     

Soil Stress Measurement: Part I. Transducer in a Uniform Stress Field

In this paper, the finite element method is used to examine the stresses predicted around transducers in a uniform applied vertical stress field. Vertical transducers and stress state transducers, disturbed zones (both weaker and stronger) around the transducer and the influence of soil shear and compression properties are all considered.Very thin (1–2 mm) disturbed zones alter the stresses estimated using transducers. When the disturbed zone around the transducer is weaker than the undisturbed soil, both vertical and stress state transducers underestimate stresses. When there is no disturbed zone, or when the disturbed zone is stronger than the surrounding soil, the transducers overestimate the stresses except in wet, weak soil. In wet, weak soil the stresses may be close to hydrostatic and accurate estimates of the applied stresses in the soil might be obtained. In general, however, it would appear that the stress transducers are unlikely to yield accurate estimates of the applied stresses in a uniform stress field.Many factors influence the stresses estimated by soil stress transducers. There is no general means of correcting the results to infer the applied stresses in a uniform stress field, other than by a detailed analysis of the sort described here. Inferences drawn from absolute values should be treated with caution and subject to detailed analysis.     

内燃机燃烧模型的发展现状

利用CFD技术对内燃机燃烧过程进行数值模拟已成为内燃机研究的重要工具。选用恰当的燃烧模型对准确预测内燃机燃烧过程具有重要意义。内燃机CFD燃烧模型主要针对自燃、预混燃烧和非预混燃烧3种燃烧模式,其中有些模型可以同时模拟2种模式或3种模式。内燃机新的燃烧系统的不断出现促进了燃烧模型的发展。本文以STAR—CD和FIRE软件为出发点,介绍了内燃机燃烧模型的发展现状。     

四气门直喷式柴油机缸内流场试验研究

通过螺旋气道与不同进口面积切向气道的组合试验，分析了各种组合进气系统的流通特性，发现通过改变切向气道进口面积就能很容易地实现涡流比的调节。利用热线风速仪对模拟缸内空气流动进行了测量，结果表明4气门柴油机进气过程中在远离缸盖的平面内形成稳定的旋涡，其涡流中心偏离气缸中心。揭示了4气门柴油机进气涡流的形成过程及缸内流场的特点，详细探讨了切向气道进口面积和气门升程对缸内流场的影响。     

Drainage effects on spatial variability of soil electrical conductivity in a vertisol

Spatial variability of soil electrical conductivity (EC) is characterized in a 33 ha plot before and 2 years after drainage initiation. Measurements of EC were made in a square grid at 50 m spacing and at 0–20, 20–40, 40–60 and 0–60 cm depths. Both mean EC values and coefficients of variation (CV) are reduced after drainage. The frequency histograms show that EC fits to a lognormal distribution before drainage, whereas it seems to be normally distributed after drainage initiation. The bimodality found in histograms before drainage was not observed after it. Spatial structure of soil EC is strongest at 0–20 cm before drainage and it is weaker at greatest depths. Nevertheless, the semi-variogram at 40–60 cm after drainage shows a more remarkable spatial structure. EC spatial variability shows anisotropy before drainage, which was related to topography. However, directional semi-variograms after drainage did not show such anisotropy. In conclusion, drainage not only reduces EC values, but also notably changes EC spatial variability.