Fluoride adsorption by a saline sodic soil irrigated with a high F water     

C. W. Robbins 《Irrigation Science》1986,7(2):107-112

Summary Langmuir isotherm data for F adsorption were obtained from 1:10 soil:water extracts of soil samples from a lysimeter study. A sodic silt loam surface soil with a saline sodic subsoil was irrigated with a high sodium chloride, high fluoride (0.38 mMF) geothermal well water. A previous study showed that fluorite (CaF₂) was precipitated from solution in the upper portion of this profile while another mechanism removed F solution in the lower part of the profile to below 0.02 mMF. The Langmuir isotherm data indi cate that one kind of surfaces or sites remove fluoride from solution over the 0 to 1.1 to 1.2 mMF range. The adsorption capacity for this F removal is about 4.4 to 5.8 mmol F/kg of soil and the equilibrium constant is between 0.54 to 1.001/mmol F. Once these surfaces or sites were saturated, a second kind of sites removed F from solution, and had an adsorption capacity of 9.2 to 11.4 mmol/kg and an equilibrium constant of 0.16 to 0.271/mmol. Both data sets fit the Langmuir equation. At some point before or after this second set of sites or surfaces was saturated, the fluorite ion activity product was exceeded and fluoride was then removed from solution via fluorite precipitation. The two adsorption mechanisms lowered the soil solution F concentration sufficiently to prevent ground water contamination, but once the adsorption sites were saturated, fluorite precipitation does not decrease F concentration sufficiently to meet drinking water standards.Contribution from USDA-ARS, Snake River Conservation Research Center, Kimberly, ID 83341, USA  相似文献   

Book review     

W. Wolters 《Irrigation and Drainage Systems》1988,2(3):279-280

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Evaluating evaporation from field crops using airborne radiometry and ground-based meteorological data     

Ray D. Jackson  M. Susan Moran  Lloyd W. Gay  Lee H. Raymond 《Irrigation Science》1987,8(2):81-90

Summary Airborne measurements of reflected solar and emitted thermal radiation were combined with ground-based measurements of incoming solar radiation, air temperature, windspeed, and vapor pressure to calculate instantaneous evaporation (LE) rates using a form of the Penman equation. Estimates of evaporation over cotton, wheat, and alfalfa fields were obtained on 5 days during a one-year period. A Bowen ratio apparatus, employed simultaneously, provided ground-based measurements of evaporation. Comparison of the airborne and ground techniques showed good agreement, with the greatest difference being about 12% for the instantaneous values. Estimates of daily (24 h) evaporation were made from the instantaneous data. On three of the five days, the difference between the two techniques was less than 8%, with the greatest difference being 25%. The results demonstrate that airborne remote sensing techniques can be used to obtain spatially distributed values of evaporation over agricultural fields.  相似文献   

Drainage and vertical hydraulic conductivity of some Dutch “knik” clay soils     

J. Bouma  L. W. Dekker  H. L. Verlinden 《Agricultural Water Management》1976,1(1):67-78

The vertical K-sat of a clay layer, occurring between 30 and 60 cm below the soil surface, was measured in situ in early spring at thirteen sites, using large soil columns. Gypsum was used to form a barrier around the column and K-sat values were measured with an infiltrometer in columns that were first attached and then detached from the subsoil. This procedure allows an estimate of the occurrence of large continuous pores, such as vertical worm channels. Highest values were found in tile-drained grassland, followed by grassland with surface drainage only, and by tile-drained arable land. Relatively low K-sat for the silty subsoil, rather than the (high) vertical K-sat for the clay layer, is considered to be responsible for high groundwater tables in the wet season.Undisturbed, large columns were taken to the laboratory and saturated for a period of three months to simulate prolonged swelling after a very wet season, and to measure chloride-breakthrough curves, for characterizing soil-pore continuity. The clay layer, sampled in the surface-drained grassland, showed no significant reduction of K-sat after prolonged swelling, but the one for arable land was reduced. Moreover, flow in the latter occurred through only a few relatively large, continuous pores, whereas a more heterogeneous pore system was found for the column from grassland. The already high K-sat of the clay layer in surface-drained grassland increased as a result of tile drainage. Compaction of the clay layer in tile-drained arable land reduced K-sat well below the level found in surface-drained grassland.  相似文献   

An integrated modelling toolbox for water resources assessment and management in highland catchments: Model description     

R.A. Letcher  B.F.W. Croke  A.J. Jakeman  W.S. Merritt 《Agricultural Systems》2006

Water and land resource competition and environmental degradation pose difficult questions for resource managers. In particular, the ensuing trade-offs between economic, environmental, and social factors and their spatiotemporal variability must be considered when implementing management policies. This paper describes an integrated modelling toolbox that has been developed for highland catchments – specifically the Mae Chaem catchment in Northern Thailand. This toolbox contains models of crop growth, erosion and rainfall-runoff, as well as household decision and socioeconomic impact models. The approach described advances and complements previous approaches by: considering more complex interactions between land-use decisions and the hydrological cycle; modelling household decisions based on uncertain expectations; and assessing impacts of changes not only on flows and household income, but also on subsistence production and erosion. An example of the types of trade-offs and scenarios that can be assessed using the integrated modelling toolbox is also presented. This demonstrates that for the scenarios presented, the magnitude and direction of impacts simulated by the model is not dependent on climate. Further testing of the model is demonstrated in a companion paper. Overall, the plausibility of the model is shown.  相似文献   

Roots in irrigated clay soils: Measurement techniques and responses to rootzone conditions     

W. S. Meyer  H. D. Barrs 《Irrigation Science》1991,12(3):125-134

Summary This paper reviews research carried out at the Griffith Laboratory in Australia over the last decade on techniques for, and results of, observations of roots in irrigated clay soils. Our results emphasise the adaptability of root systems to rootzone conditions. Experiences with techniques for observing roots non-destructively in the field and both non-destructively and destructively in lysimeters are described. We concluded that the minirhizotron technique, applied in the field, was unreliable under our conditions. Horizontal root observation tubes were used in lysimeters to measure root length density (RLD) and to assess whether roots were clumped together or randomly distributed. Destructive sampling and measurement of RLD was used to establish a theoretical relationship between root intercept counts along the tubes and RLD. The application of image analysis to both destructive and non-destructive sampling in the lysimeters is outlined. The non-destructive lysimeter studies showed that roots were significantly clumped. Analysis of root intercept and root hole counts on the faces of sample cubes taken from the lysimeters showed root distribution was anisotropic over the whole soil profile for both safflower and wheat. There were many more roots and root holes present in the sampled soil cubes than was indicated by independent sampling for washed out RLD. Safflower appeared to have a faster turnover of roots than did wheat or maize. Lysimeters, equipped with horizontal root observation tubes, enabled studies to be made of many factors affecting root growth. Soils affect where and how fast roots grow, although there is also a strong species interaction. For example, soybean roots proliferated above a fresh water table in one soil but not in another; wheat had little tendency to proliferate above the water table in either soil. In wet soils, roots cease to grow once soil oxygen levels decrease below 10 mg O₂ l _soil ^-1 . This level should form the basis for soil drainage criteria. In drying soils, roots will grow successively into soil regions containing soil water: the level of adaptation being determined by soil conditions, crop growth stage and level of evaporative demand. The methods of root observation used in our studies have given quantitative assessment of root distribution. However, further research is needed to link horizontal and vertical root distribution and root adaptation more strongly to crop development and soil conditions.  相似文献   

Effects of soil type on soybean crop water use in weighing lysimeters     

W. A. Dugas  W. S. Meyer  H. D. Barrs  R. J. Fleetwood 《Irrigation Science》1990,11(2):69-75

Summary Different soils are known to affect the amount and distribution of both available water and roots. Optimising irrigation water use, especially when shallow water-tables are present requires accurate knowledge of the root zone dynamics. This study was conducted to determine the effect of two soil types on root growth, soil water extraction patterns, and contributions of a water-table to crop evaporation (E). Two weighing lysimeters (L1 and L2) with undisturbed blocks of soil were used. The soil in L1 had higher hydraulic conductivity and lower bulk density than that in L2. Well watered conditions were maintained by irrigation for the first 110 days from sowing (DFS). Root length density (RLD) was calculated from observations made in clear acrylic tubes installed into the sides of the lysimeters. Volumetric soil water contents were measured with a neutron probe. A water-table (EC = 0.01 S m^-1) was established 1 m below the soil surface 18 DFS. RLD values were greater in L1 than L2 at any depth. In L1, maximum RLD values (3 × 10⁴ m m^-3) were measured immediately above the water-table at physiological maturity (133 DFS). In L2, maximum RLD values (1.5 × 10⁴ m m^-3) were measured at 0.42 m on 120 DFS and few roots were present above the water-table. From 71 to 74 DFS, 55 and 64% of E was extracted from above 0.2 m for L1 and L2, respectively. In L2, extraction was essentially limited to the upper 0.4 m, while L1 extraction was to 0.8 m depth. Around 100 DFS the water-table contributed 29% (L1) and 7% (L2) of the water evaporated. This proportion increased rapidly as the upper soil layers dried following the last substantial irrigation 106 DFS. Over the whole season the water-table contributed 24% in L1 and 6.5% in L2 of total E.  相似文献   

Water uses and productivity of irrigation systems     

A. J. Clemmens  D. J. Molden 《Irrigation Science》2007,25(3):247-261

Reducing overall water diversions for agriculture, while maintaining or increasing production to keep up with increasing world population, has been and will continue to be a challenge. Yet there is not good agreement regarding the programs needed to improve the productivity of agricultural water use, nor what increases are feasible. It is recognized that field irrigation is inherently nonuniform. So also is the distribution of water to users and water delivery service nonuniform. Here, we suggest that crop-scale irrigation uniformity can be examined at a project scale by understanding how field, farm and project irrigation systems contribute to nonuniformity. We also discuss the interrelation between project scale uniformity and the relative irrigation water supply, and their combined impact on project productivity. We provide an example which relates internal measures of project performance (e.g., water distribution operations) and external measures of project performance (e.g., project-wise water productivity).  相似文献   

Simulation of drainage water quality with DRAINMOD     

R. W. Skaggs  M. A. Brevé  A. T. Mohammad  J. E. Parsons  J. W. Gilliam 《Irrigation and Drainage Systems》1995,9(3):259-277

The design and management of drainage systems should consider impacts on drainage water quality and receiving streams, as well as on agricultural productivity. Two simulation models that are being developed to predict these impacts are briefly described. DRAINMOD-N uses hydrologic predictions by DRAINMOD, including daily soil water fluxes, in numerical solutions to the advective-dispersive-reactive (ADR) equation to describe movement and fate of NO₃-N in shallow water table soils. DRAINMOD- CREAMS links DRAINMOD hydrology with submodels in CREAMS to predict effects of drainage treatment and controlled drainage losses of sediment and agricultural chemicals via surface runoff. The models were applied to analyze effects of drainage intensity on a Portsmouth sandy loam in eastern North Carolina. Depending on surface depressional storage, agricultural production objectives could be satisfied with drain spacings of 40 m or less. Predicted effects of drainage design and management on NO₃-N losses were substantial. Increasing drain spacing from 20 m to 40 m reduced predicted NO₃-N losses by over 45% for both good and poor surface drainage. Controlled drainage further decreases NO₃-N losses. For example, predicted average annual NO₃-N losses for a 30 m spacing were reduced 50% by controlled drainage. Splitting the application of nitrogen fertilizer, so that 100 kg/ha is applied at planting and 50 kg/ha is applied 37 days later, reduced average predicted NO₃-N losses but by only 5 to 6%. This practice was more effective in years when heavy rainfall occurred directly after planting. In contrast to effects on NO₃-N losses, reducing drainage intensity by increasing drain spacing or use of controlled drainage increased predicted losses of sediment and phosphorus (P). These losses were small for relatively flat conditions (0.2% slope), but may be large for even moderate slopes. For example, predicted sediment losses for a 2% slope exceeded 8000 kg/ha for a poorly drained condition (drain spacing of 100 m), but were reduced to 2100 kg/ha for a 20 m spacing. Agricultural production and water quality goals are sometimes in conflict. Our results indicate that simulation modeling can be used to examine the benefits of alternative designs and management strategies, from both production and environmental points-of-view. The utility of this methodology places additional emphasis on the need for field experiments to test the validity of the models over a range of soil, site and climatological conditions.  相似文献   

A tool for community-based assessment of the implications of development on water security in hillside watersheds   总被引：1，自引：0，他引：1  

J. C. Luijten  E. B. Knapp  J. W. Jones 《Agricultural Systems》2001,70(2-3):603-622

Development and population growth in Latin American countries with steep slope farming are likely to further increase pressures on water and land resources. A methodology was developed for assessing water availability and use under different development pathways at a watershed scale to determine whether water security is a potential problem, and if so, under what conditions it is likely to occur. This methodology makes use of a GIS-based spatial water budget model for simulating stream water availability, water use and stream flow control on a daily basis at a watershed scale. Here, we analysed water availability under three plausible development scenarios for the 3246 ha Cabuyal River watershed in southwest Colombia in the year 2025: Corporate Farming (CF), Ecological Watershed (EW), and Business as Usual (BU). Simulated average river flows at the watershed outlet were, respectively, 874, 796 and 925 l s⁻¹ for the CF, EW and BU scenarios. The contribution of base flow to river flow (base flow index) was on average, 80.8, 85.6 and 77.9%, respectively, for the three scenarios. The watershed had the potential to meet the anticipated increase in water use under each explorative scenario. However, dams were necessary to store irrigation water in the CF scenario, otherwise over 60% of the available water would have been used during the dry season. Such a high figure raises concerns about effects on aquatic and riparian ecology, concentrations of potential contaminants, water reserves for especially low rainfall years, and the watershed resilience to meet temporarily higher water needs during the day. Analyses indicated that current water-use conflicts in the watershed can be resolved if irrigation water supply is separated from drinking water supply. This study helped reduce some of the complexity associated with the interdependencies between land and water resources, the impact of using them, and spatial linkages within the watershed. Results of this study can be used for teaching local stakeholders about basic landscape responses and helping multi-institutional alliances to become proactive and to guide development to the benefit of local communities.  相似文献