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This paper aims to present the three kinds of water footprint of sugarcane in eastern Thailand. The water footprints of sugarcane were assessed as the volume of yield in water per product unit (m3/ton). Because of, sugarcane is an important crop in Thailand. The residue left from sugarcane can develop into useful products include fuel to produce electricity, organic fertilizers, pulp and scientific material. In present, area for sugarcane is likely to add more acreage. The cultivated area would affect the use of water resources. Therefore, the study the water footprint of sugarcane is an important crop. The result water footprint of sugarcane from the period 2013 - 2014 is 178.32 m3/ton (129.60 m3/ton of green water footprint, 17.61 m3/ton of blue water footprint and 31.11 m3/ton of grey water footprint). The highest and lowest water footprints are Prachinburi and Chonburi respectively. The water footprint in the eastern Thailand for sugarcane is lower than the global average. Excepting, the grey water footprint is about 3 times higher than that. This is mainly because of high fertilizers application rate for sugarcane are 125 - 156.25 kg/ha. Another one, the water footprint can be using prediction implement of yield of sugarcane.

The use of contaminated water to irrigate crops by surface, sprinkler, or conventional drip irrigation represents a significant public health concern due to the presence of multiple microbial pathogens associated with gastrointestinal disease. In this study, Escherichia coli and MS2 bacteriophage were used as microbial surrogates to evaluate the contamination of romaine lettuce (Lactuca sativa L. var. longifolia) using bottom watering pots simulating a subsurface drip irrigation (SDI) system in a greenhouse. The primary goal was to determine whether the exposure of lettuce plants to E. coli and MS2 would result in detectable levels of these microorganisms associated with the edible portions of plants. Plants were grown in bottom watering pots and were irrigated the last twelve days before harvesting with contaminated water containing E. coli and MS2 phage at 109 CFU/ml and 1011 PFU/ml, respectively. Harvested plants were processed to determine if E. coli or MS2 was associated with the plant surfaces or within the plant tissues. None of the samples was positive for either E. coli or MS2 bacteriophage, suggesting that subsurface irrigation systems effectively reduce the risk of produce-contamination with bacterial and viral pathogens.

Alfalfa provides high-energy feed for dairy cows and other livestock. This crop is also known for its high water-use efficiency. Subsurface drip irrigation (SDI) is an ideal method for meet...

Introduction: A major design issue in implementing a subsurface drip irrigation (SDI) system is determining the appropriate drip tape placement depth to allow basic farming operations while still providing adequate water to the crop. Objective: To determine the appropriate placement depth of the SDI tapes using modeling techniques and classical soil mechanics theory. Methodology: The HYDRUS-2D program was used to determine the wetting pattern, after 12 h of irrigation, of a SDI emitter installed at 50 cm depth in three soil types: sandy clay loam (SCL), clay loam (CL) and loam (L), and classical soil mechanics theory was used to calculate the increase in soil stress at different depths. Results: The vertical capillary rise above the dripline was 27, 30 and 22 cm for SCL, CL and LF soils, respectively. The minimum dripline placement depth to avoid failure is 40 cm in SCL and L soils, and 35 cm for CL soil. Study limitations: The physical properties and hydraulic parameters of the soil were obtained from the literature, and the soil mechanics theory results were not calibrated with field measurements. Originality: This is the first study in which soil mechanics is used to determine the spacing and installation depth of SDI system tapes. Conclusions: This type of study is helpful in determining the SDI dripline placement depth to ensure adequate trafficability under these irrigation system

We model the soil water balance in arid regions of Mexico.The stochastic simulation model computes probability of crop failure.The model may compute potential crop yield under climate change scenario B2.The model is linked to a knowledge base for supporting decisions.Data base includes maps of potential crops within the region of interest. Rural inhabitants of arid lands constantly face a lack of sufficient water to fulfill their agricultural and household needs. In this situation they have to take quick and precise decisions about how to cope with the situation. Moreover, there is not readily available technical information to support their decisions regarding the course of action they should follow to handle the agro-climatic risk. In this paper a computer model (soil water balance model) is described to assess the impact on crops yields of rainfall shortages in dry lands in Mexico. The model is linked to a knowledge based database where a farmer may find readily available information to support cropping decisions. The knowledge base activates when the computed average crop yield is less than the 50% of the expected crop yield. The knowledge base provides information on risk, potential crops, and the geographical location (counties) where the crop may succeed. Also, it provides a technology to increase water productivity under limited availability situations. Further, the model can evaluate the impact of a climate change scenario (IPCC B2). Other inputs to the model being equal, the user may shift the model to run the climate change scenario and to compare the outputs of the model to assess the climate change impact on future crops yields.

Reliable estimates of crop water use are essential to economic production of sweet sorghum under irrigated conditions. In Tucson, Arizona, USA, two planting dates, May 5th and June 15th, and four sweet sorghum varieties (M81E, ST, SM and A4) were evaluated to estimate crop coefficients (kc) based on the heat unit accumulation concept (GDD). One irrigation level at 50% depletion of available water capacity prior to irrigation and its effect on juice, biomass and ethanol yields was evaluated. Results show that it was possible to develop heat unit based kc´s for two day-neutral varieties (ST and SM) and that they required 25% less water than the photo-sensitive varieties. Peak crop coefficients were determined as 1.13, 1.05, 1.16 and 1.22 for M81E, ST, SM and A4. Results also showed that growing degree days accumulated to flowering were 2226 and 1759 GDD for ST and SM respectively. At a P-value of 5% there were differences in crop water use, juice yields and bagasse production among treatments. For the May planting there was a slight effect on ethanol yields but no effect for the June planting, showing that regardless of the planting date and variety they are more likely to be similar. Copyright © 2015 John Wiley & Sons, Ltd.

The purpose of this paper is to present preliminary results from testing a pilot-scale sweet sorghum diffusion extractor that was designed to extract the juice from sweet sorghum stalks while simultaneously filtrating the extracted juice. The ultimate use of the juice is fuel grade ethanol. In essence, the system is a large coffee percolator that works by running shredded sorghum through a conveyor with recirculating hot water running over the crop to extract the sugar through diffusion. The current system spans 10 m in length, is 1m wide, and 0.6 m high. The sorghum is harvested with a forage chopper, and discharged at a constant rate into the trough. The sorghum moves at a rate of 0.2 m per minute, so the sorghum is in the diffusion system for 20 minutes. The water/juice is sprayed over the chopped stalks and is kept at a target temperature of 660C. A roller fixture located at the end of the trough helps squeeze out some of the remaining juice. The pilot scale sweet sorghum diffusion system continuously extracts the sugar at a rate of 3 metric tons (mt) of sorghum an hour with a minimum sugar extraction of 60%. During our pilot testing phase we were able to process 0.65 mt of material per hour with a resultant brix of 6%. The system was halted several times to adjust the heating system, so we are confident that with further testing we can process at least 3 mt per hour of material. The conversion from the conventional harvesting and roller press of the sorghum stalk to this method could resulted in a 66% reduction in energy to harvest and extract the juice.

Recycling of the nutrient solution used to irrigate fruit and vegetables in greenhouses can increase water use efficiency and reduce the contamination of local water sources. The nutrient solution cannot be recycled without treatment because of potential contamination of the entire plant system with bacteria, viruses, and/or fungi. Ozonation, pasteurization and chemigation are the typical techniques used, but are often expensive and not always effective [. Slow sand filter (SSF) is a technology that is relatively inexpensive to purchase and operate. Data was collected from two SSF to verify treatment efficacy and associated hydraulic characteristics. The SSF was able to consistently produce water with a turbidity less than 1 Nephelometric Turbidity Units (NTU) and with the infiltration capacity to treat 0.27 m3 m-2 h-1 of greenhouse effluent; which, equates to treating 3,600 L d-1 of drainage water from a 1,000 m2 greenhouse. The recovery rate for the filter was an average of 110 minutes. Ideal growing conditions for bacteria responsible for the treatment of the water in the SSF included warm and consistent water temperature, high nutrient content, and organic loading in the water. The SSF was able to sustain the hydraulic loading rate of 0.27 m3 m-2 h-1 for 16 days. At the end of this period the organic layer that was present at the sand/water interface reduced the infiltration rate because of the formation of the Schmutzdecke layer (SL). An air/water jet cleaning system scoured the SL and suspended it so that it could be drained.

article i nfo Land surface model parameter estimation can be performed using soil moisture information provided by synthetic aperture radar imagery. The presence of speckle necessitates aggregating backscatter measure- ments over large (N100 m×100 m) land areas in order to derive reliable soil moisture information from imagery, and a model calibrated to such aggregated information can only provide estimates of soil moisture at spatial resolutions required for reliable speckle accounting. A method utilizing the likelihood formulation of a probabilistic speckle model as the calibration objective function is proposed which will allow for calibrating land surface models directly to radar backscatter intensity measurements in a way which simultaneously accounts for model parameter- and speckle-induced uncertainty. The method is demon- strated using the NOAH land surface model and Advanced Integral Equation Method (AIEM) backscatter model calibrated to SAR imagery of an area in the Southwestern United States, and validated against in situ soil moisture measurements. At spatial resolutions finer than 100 m×100 m NOAH and AIEM calibrated using the proposed radar intensity likelihood parameter estimation algorithm predict surface level soil moisture to within 4% volumetric water content 95% of the time, which is an improvement over a 95% prediction confidence of 10% volumetric water content by the same models calibrated directly to soil moisture information derived from synthetic aperture radar imagery at the same scales. Results suggest that much of this improvement is due to increased ability to simultaneously estimate NOAH parameters and AIEM surface roughness parameters.

The Unified Animal Feeding Operation Strategy requires that field application of animal waste, a common fertilization and disposal practice, may not exceed crop nutrient needs. Additional guidelines set forth by the Arizona Department of Environmental Quality state that animal waste applications on agricultural fields in designated Confined Animal Feeding Operations (CAFOs) must be made in a manner such that the total N applied to the field cannot exceed the uptake from the crop grown. Because alfalfa is grown year round and can take up large quantities of N, many operators of CAFOs apply animal waste to their production alfalfa fields as method of waste disposal. In this research, fresh and composted dairy manure was applied to plots in a production alfalfa (Medicago sativa L.) field to determine the impact on alfalfa yield, soil nitrogen (N), phosphorus (P), and electrical conductivity (EC) levels and the potential for nitrate (NO3) and phosphate (PO4) leaching. Unfertilized plots were maintained as controls. Fresh and composted manure was applied to fertilized plots after each harvest at a rate intended to replace N removed from the previous cutting. After 1.5 yr and 13 cuttings, soil analysis down to 150 cm depth showed no significant difference in soil N between treatments. At study end, NO3–N made up 1.1% of total N in the fertilized plots but only 0.6% in control plots. Changes in soil N were not significant. Soil P content increased in fertilized plots but remained stable in control plots. Final soil PO4 measurements were 16, 99, and 116 kg ha 21 in the control, manure-treated, and compost-treated plots, respectively. Leachate from three drainage lysimeters contained no detectable NO3 or PO4 from any of the treatments. LSD showed no difference in EC between the beginning and the end of study, and alfalfa yield did not vary among treatments.

The Alto Rio Lerma Irrigation District, located in the state of Guanajuato in Mexico, is an agricultural area whose sustainability depends partially upon groundwater withdrawal for crop irrigation. Because of high pumping demands and current land-management practices, groundwater levels have declined severely, resulting in aquifer overdraft. In order to analyze economic, environmental, and water use problems in this region, 12 potential cropping patterns were generated for different groundwater withdrawals using linear programming. Then, simulation of the agricultural system was performed using GLEAMS to estimate the amounts of water, nitrate, and pesticides in both runoff and percolation for each cropping pattern. Pumping costs and an aquifer exploitation coefficient account for the economic and environmental impacts of aquifer overdraft. Finally, the Range of Value Method (multicriteria method) was applied to rank and identify the best cropping pattern. The results show the best alternative for effectiv...

A two year field study (1996/97 and 1997/98 growing seasons) was carried out at the Maricopa Agricultural Center (33º04'07" N; 111º57'18" W) of the University of Arizona, USA, to investigate the water use and to derive Kc's for subsurface drip-irrigated head lettuce grown in small weighable lysimeters. Measurement periods ranged from 480 to 1100 ºC-day (96/97) and from 439 to 1098 ºC-day (97/98). These intervals corresponded essentially to the second half of the crop cycle which amounted to a 1100 ºC-day, on average. The lysimeters were weighed periodically and the computation of the water balance revealed an average water use of 117 mm. Basal crop Kc was expressed as a function of cumulative growing degree days following a multiple linear regression procedure in which the data were fitted with a Fourier sine series model with up to six coefficients. Two-year Kc curves were obtained based on the Hargreaves, FAO Penman and FAO Penman-Monteith equations and compared to the AZSCHED (AriZona SCHEDuling) irrigation package. Predicted Kc peaked 0.88, 0.80 and 0.81 with the Hargreaves, FAO Penman, FAO Penman-Monteith equations, respectively, in the range of 1000 to 1050 ºC-day, in contrast to AZSCHED which predicted the peak Kc to be 1.01 at 1150 ºC-day.Um estudo conduzido na Fazenda Experimental Maricopa (33º04'07" N; 111º57'18" W), pertencente à Universidade do Arizona, USA, nos anos agrícolas de 1996/97 e 1997/98, objetivou determinar o uso de água e derivar coeficientes de cultura (Kc) da alface de cabeça irrigada por gotejamento subsuperficial e cultivada em lisímetros de pesagem intermitente. O período de medições, expresso em graus-dia acumulados, variou de 480 a 1100 ºC-dia em 96/97 e de 439 a 1098 ºC-dia em 97/98. Esses intervalos corresponderam à segunda metade do ciclo da cultura, sendo que até a colheita somou-se uma média de 1100 ºC-dia. Os lisímetros eram pesados periodicamente e o balanço hídrico revelou um consumo médio de 117 mm, naqueles períodos. O Kc basal foi relacionado com o acúmulo de graus-dia através de regressão múltipla, seguindo um modelo dado por uma série seno de Fourier, com até seis coeficientes. As curvas de Kc foram determinadas com base nos métodos de Hargreaves, FAO Penman e FAO Penman-Monteith, para cálculo da ETo e comparadas por aquela gerada pelo programa AZSCHED (AriZona SCHEDuling) de manejo da irrigação. Valores máximos de Kc estimados foram 0,88 (método de Hargreaves), 0,80 (FAO Penman) e 0,81 (FAO Penman-Monteith) no intervalo de 1000 a 1050 ºC dia, inferiores a 1,01 em 1150 ºC dia, que é o máximo Kc previsto pelo programa AZSCHED.

Nitrate contamination of surface and groundwater has become a serious concern in many agricultural areas throughout the world. Nitrate fertilization is widely used to increase crop yields and quality, but nitrates are highly soluble in water with low retention by soils. Appropriate nitrate application practices can minimize losses, but untimely rainfall can foil management intent. A small dc electrical input has previously been reported to influence nitrate movement in wet soil. Two sets of lysimeter experiments were conducted to evaluate the effect of parallel electrodes on pH and nitrate distribution in field soils subjected to an electrical input. In one experiment, drip irrigation with injected nitrate application was used to grow Sudan grass; in the other, nitrate distribution in wet soil was observed after application of varying levels of electrical current. Increased nitrate concentration, reduced sodium and calcium concentration and lower pH values near the anode, the expected results, were not attained consistently in the test soils with an electrical input of 100–700 mA. The evaluation is being continued with simpler, more controlled conditions in soil column laboratory experiments.

A key component in the calculation of reference crop evapotranspiration (ETr) is the weather data. If the weather data have been collected from a station under nonreference conditions, the data itself may contain errors, which will in turn yield inaccurate ETr estimates. It was proposed by Allen in 1996 that data used for evapotranspiration be scrutinized by comparing daily minimum temperature (Tmin) and the daily average dew point temperature (Tdew). If the difference between Tmin and Tdew is greater than 3°C, then the site is considered to be arid (nonreference) and adjustments are recommended for temperature and dew point data. In Arizona, normal weather conditions often occur where Tmin and Tdew do not approach each other. This study examined the appropriateness of applying the conditions set forth by Allen to temperature data collected in central Arizona. Two weather stations were set up in a 35.5ha alfalfa field in central Arizona to measure dry bulb and wet bulb temperatures. Additionally, plant te...

Une methodologie precise de programmation de l'irrigation est necessaire pour les cultures sensibles aux stress hydrique et pour celles a cout de production eleve. Ceci implique un pilotage de l'irrigation fonction des stades phenologiques des cultures. Ce travail presente plusieurs parametrages de methodes de pilotage de l'irrigation bases sur les degre-jours de croissance tels que: gestion par un deficit maximal du stock d'eau du sol (MAD), par la profondeur d'enracinement (R d ) et par le coefficient cultural (K c ). Les modeles proposes ont ete appliques au pilotage de l'irrigation dans deux champs de pomme de terre sous deux systemes d'irrigation: systeme de surface et systeme par' aspersion. Les resultats indiquent que le modele predit l'irrigation d'une maniere coherente et logique. Les modeles proposes sont flexibles, adaptables et faciles a mettre en oeuvre dans les logiciels de pilotage de l'irriguation.

In arid areas where the available water is limited and randomly changing with time, the surface irrigation might still be the best option due to economic and other considerations. Hence, the irrigation delivery system should be sized in such a way that the allocation of available surface water to different crops at any time yields maximum possible revenues. This can be ultimately achieved with the aid of a two-stage optimal formulation combining the present design stage with the future operational conditions. This work applies two stochastic mathematical techniques to determine the optimal sizes of a hypothetical surface irrigation delivery system subjected to varying deficit levels of available water and considering the uncertainties associated with the available water and the crop revenues. Canal sizes represented the first-stage decisions while the future water allocations were made in the second stage. The Regularized Stochastic Decomposition approach solved the case of stochastic available w...

A mobile weighing system was designed in 1994 to weigh small lysimeters to measure water use by shallow-rooted crops. Using a reconditioned pesticide sprayer, a hoist, and a weighmeter, small lysimeters were weighed in the 1995, 1996, and 1997 growing seasons. The lysimeters were constructed of 4.8-mm hot-rolled steel and were 0.91 x 1.02 x 0.61 m in size with an internal area of 0.929 m 2 . The weight of a lysimeter containing only moist soil was 1.110.27 kg. At the beginning of each season of use, several tests were conducted on the weighing system to determine if it was sensitive enough to give adequate results of crop water use. In 1995, tests were conducted on linearity, repeatability, thermal shift, and creep errors. The values were ±0.062 kg, ±0.12 kg, -0.007 kg/ ° C, and -0.242 kg, respectively. The terminal linearity was 0.082 kg (1996) and 0.043 kg (1997). The measurement uncertainty decreased as the number of lifts increased. The results showed that the system was capable of producing adequate results for determining crop water use.

Contamination of surface and subsurface waters has become a major problem related to agricultural practices. Nitrate, one of the principal plant fertilizers, is the chemical having the greatest effect. This research utilized closed system laboratory experiments to evaluate the effectiveness of an electrokinetic process in concentrating and retaining nitrates close to the anode and studied the effect of selected electrokinetic system design parameters on the performance of the process. The tests demonstrated that an electrokinetic process can effectively concentrate and retain nitrate close to the anode in saturated sandy soil.

Chemicals applied to agricultural lands inevitably move below the plant root zone and may contaminate the underlying ground-water reservoirs. Laboratory open system soil column experiments were conducted to evaluate electromigration as a process for concentrating and retaining the nitrates close to the anode in soil subjected to hydraulic flow. Electromigration was found to be an effective means for concentrating and retaining nitrate close to the anode in saturated sandy soil at low flow rates. However, for a given electrical input, the effect was reduced as the hydraulic flow rate increased, being indiscernible for higher flow rates.

A framework for determining the effect of maintenance events on irrigation system flows is described. Standard definitions for corrective and preventive maintenance are presented and two maintenance objectives and six classifications are established. Maintenance activities and decision criteria common to many irrigation systems are suggested. A format for describing these and other maintenance activities is proposed. A methodology for setting decision levels for maintenance activities is presented. Maintenance cost is compared with income lost as a result of less than maximum production because water supplied was insufficient for crop requirements. This comparison demonstrates that maintenance decision levels should be set so that maximum evapotranspiration can be achieved. Budget request forms and report forms are presented with examples of actual maintenance events showing the expected and actual impact on system flows.

This paper describes a simple, few-parameters simulation model for a water harvesting-strip farming system. The model includes runoff threshold functions for different soil types, and for different initial soil water contents. The evapotranspiration component of the model accounts for dynamic root water extraction using regression equations that correlate canopy cover with root growth as a function of time. The model is simple to operate and uses readily available inputs. It can work with several crops when leaf area indices and crop stage coefficients are provided. The agreement between simulation outputs and field-observed data indicates that the model accurately describes the water balance within the system. The model is then recommended for obtaining preliminary design of water harvesting systems. A FORTRAN77 source code has been written for the simulation procedure.

The onset and rate of sap moving up the branches of grapefruit (Citrus paradisi Macfadyen) trees were monitored hourly using portable sap flow sensors at Waddell, Arizona. Hourly reference evapotranspiration (ETo) estimates were calculated using data from a nearby weather station. Crop water use was estimated from soil moisture measurements using a neutron probe. These data were used to first delineate the upper and lower temperature threshold values for the determination of heat units. A heat unit-based crop coefficient was then derived from a correlation of the crop coefficient with heat units over a crop year. The heat unit-based crop coefficient was found to be similar to crop coefficients derived by other researchers.

The University of Arizona undertook a “pilot” project to grow sweet sorghum on a field scale (rather than a plot scale), produce juice from the sweet sorghum, deliver the juice to a bio-refinery and process it to fuel-grade ethanol. We also evaluated the bagasse for suitability as a livestock feed and as a fuel. In addition to these objectives we evaluated methods of juice preservation, ligno-cellulosic conversion of the bagasse to fermentable sugars and alternative methods of juice extraction.

Migration of chemicals in soils to surface or ground water has become a serious threat in many agricultural regions, with nitrates affecting the broadest area due to intensive fertilization and nitrate solubility. This project evaluated electroreclamation utilizing subsurface horizontal drainage tubing and parallel electrodes to concentrate and remove nitrates from soil. Nitrate concentration in saturated soil tended to increase from anode to cathode after the application of a small direct-current electrical field as the nitrate solution moved toward the cathode. When soil moisture content dropped below the saturation level, the nitrate began to migrate toward the anode. Research is recommended to evaluate the effect of a broader range of electrical parameters and analyze the feasibility of commercial application.

A water allocation model was developed to recommend allocation of irrigation water to different crop fields in a canal-based irrigation project. Model components are an irrigation scheduling program to predict irrigation water demands, a crop response model to compute crop yields, and a canal delivery model to check the physical feasibility of water delivery. Multiperiod linear programming is utilized to determine the optimal allocation strategy, which maximizes irrigation benefits. Allocation constraints are irrigation water demand, irrigation water availability, canal delivery capacity, minimum irrigation limitations, and crop response model limitations. The allocation model was validated using crop, soil, canal, and irrigation management data for MAC, a University of Arizona farm.

Evaluation of the Penman-Monteith-based crop water stress index (CWSI), as a potential indicator of turf irrigation timing, requires reliable estimates of potential (minimum) canopy resistance, r cp , and aerodynamic resistance, r a . This paper compare various methods of estimating r cp and r a for evaluation of water stress of bermudagrass turfgrass (Cynodon dactylon cv. Midiron) in the desert Southwest of the USA. First, two empirical CWSI models were developed using field data collected from well-watered and severely water-stressed turf plots during the 1986 growing season in Tucson, AZ [...]

A field study assessed the accuracy and consistency of crop water stress index (CWSI) estimates determined by two empirical models and one theoretical model for evaluation of bermudagrass [Cynodon dactylon (L.) Pers. cv. Midiron] water status. The simplest empirical model, describing canopy temperature minus air temperature (T c − T a ) of well-watered turf as a linear function of air vapor pressure deficit, was inadequate for estimating CWSI, since seasonal averages of CWSI for well-watered, moderately stressed, and stressed turf had corresponding coefficients of variation of 1170, 160, and 86, respectively [...]

Aerodynamic resistance to sensible heat transfer (rah) is an important parameter in bulk resistance models of energy exchange between the Earth's surface and the atmosphere. To estimate sensible heat flux density (H) over irrigated fields, it is often necessary to evaluate rah under stable atmospheric conditions. This is because irrigated fields are often cooler than air temperature as a result of net radiative cooling at night and advective influences. Sensible heat fluxes are generally small at night, but may become a relatively large component of the surface energy budget during advective conditions. The purpose of this paper was to compare H modeled for stable conditions over an extensive area of irrigated bermudagrass (Cynodon dactylon) cv. Midiron) using three rah methods from the literature, and to determine the sensitivities of the methods to the various parameter inputs. In addition to comparing modeled H values with each other, comparisons were made with H values measured by eddy correlation over the bermudagrass. The three methods studied were expressed as functions of the bulk Richardson number (RiB). The methods differ mainly in the stability correction function, and the added resistance term (kB−1, where k is von Karman's constant and B−1 is a non-dimensional bulk parameter), which arises as a result of dissimilarities between heat and momentum transfer mechanisms near surface obstacles. Application of the methods to the bermudagrass data resulted in marked differences between the various modeled H values, and between modeled and measured H values. The modeled H values were more sensitive to surface emissivity and temperature inputs.

Biofilms can have deleterious effects on drinking water quality and may harbor pathogens. Experiments were conducted using 100 μg/liter silver to prevent biofilm formation in modified Robbins devices with polyvinyl chloride and stainless steel surfaces. No significant difference was observed on either surface between the silver treatment and the control.

We have developed ways to utilize discarded tires for erosion control structures, bank stabilization and slope stabilization and erosion control in the form of engineered structures for each of these applications. This paper also describes and illustrates a channel erosion control structure made entirely from individual tires used to form side walls, wing walls and aprons for the structure. In this case the individual tires were bound together with nylon rope to form a flexible structure. This structure was built in a ephemeral wash (gully) on a local ranch near Tucson, AZ and has been in place for over ten years.

This study was conducted to assess the efficacy of silver as a secondary disinfectant to replace or reduce the level of chlorine utilized in water distribution systems. Pseudomonas aeruginosa and Aeromonas hydrophila are opportunistic pathogens present in drinking water and have been associated with waterborne disease. After 8 hours of exposure to 100 microg/L of silver, there was a >6-log10 reduction in P. aeruginosa in tap water at room temperature at pH7 and a 5.55-log10 reduction in the presence of 3 mg/L humic acid. Similar reductions were observed at pH9. At 4 degrees C, reductions greater than 4-log10 were observed after 24 hours. For A. hydrophila, a >6-log10 reduction occurred at both pH7 and pH9 within nine hours. The World Health Organization has determined that this amount of silver could be used for water disinfection without health risks. Furthermore, silver shows promise as a secondary disinfectant, even in the presence of organic matter in concentrations that would reduce the effectiveness of free chlorine.

A two year field study (1996/97 and 1997/98 growing seasons) was carried out at the Maricopa Agricultural Center (33º04'07" N; 111º57'18" W) of the University of Arizona, USA, to investigate the water use and to derive Kc's for subsurface drip-irrigated head lettuce grown in small weighable lysimeters. Measurement periods ranged from 480 to 1100 ºC-day (96/97) and from 439 to 1098 ºC-day (97/98). These intervals corresponded essentially to the second half of the crop cycle which amounted to a 1100 ºC-day, on average. The lysimeters were weighed periodically and the computation of the water balance revealed an average water use of 117 mm. Basal crop Kc was expressed as a function of cumulative growing degree days following a multiple linear regression procedure in which the data were fitted with a Fourier sine series model with up to six coefficients. Two-year Kc curves were obtained based on the Hargreaves, FAO Penman and FAO Penman-Monteith equations and compared to the AZSCHED (AriZona SCHEDuling) irrigation package. Predicted Kc peaked 0.88, 0.80 and 0.81 with the Hargreaves, FAO Penman, FAO Penman-Monteith equations, respectively, in the range of 1000 to 1050 ºC-day, in contrast to AZSCHED which predicted the peak Kc to be 1.01 at 1150 ºC-day.

This study was initiated to develop and assess the management of the application of animal waste and compost to an oat/corn rotation in Arizona. Unlike many Eastern states, Arizona uses nitrogen as the limiting nutrient in animal waste applications. In this project, nutrient analysis for nitrogen, phosphorus and electroconductivity were conducted on soil, manure/compost, and plant samples. There were three treatments replicated four times in this study. Treatment 1: inorganic nitrogen sources; Treatment 2: manure; Treatment 3: composted manure. All management decisions are made to maximize yield while assuring that the amount of nitrogen applied was equivalent to the nitrogen removed in the crop. In the first year, there was little or no difference in crop yields. In the second year, yield differences began to show. The soil nitrate-N content was remaining relatively low and equal between treatments. However soil phosphorus content has significantly increased in the manure and compost plots. According to the ruling, if the level of P becomes high enough, then P will become the limiting nutrient. Thus far, we have not reached that point; however, P levels are being monitored closely.

This study was initiated to determine the biological and nutrient impacts of manure and compost applications on an oat/corn rotation in Central Arizona. Bacterial analysis for E.Coli, Listeria and coliphage and nutrient analysis for nitrogen, phosphorus and electroconductivity were conducted on soil, manure/compost, irrigation water, drainage water and plant samples. The presence of endocrine disruptors was also tested on the irrigation and drainage water. After a single season of oats, there doesn't appear to be any significant increase in the presence of bacteria in the soil-water- plant environment. Endocrine disruptors were detected in drainage and irrigation water samples. Nitrate leaching is occurring but at relatively low rates. Oat forage yields between treatments were all over 10,000 kg/ha and there was no statistically significant difference between them.

Soluble chemicals applied to soils have been identified as major sources of surface and groundwater contamination. This research examined the application of a small dc electrical input to attract and retain nitrates in the root zone of drip irrigated barley in small lysimeter trials. Nitrate content near the anode was higher and pH lower, as desired, during a portion of the test. However, the electrical input seemed to have little effect on nitrate distribution at other times, perhaps due to careful management of water and nitrate inputs. These results indicate a potential benefit of an electrical input to the control of nitrate transport in soil.

The effect of three vigor-control apple (Malus domestics Borkh.) rootstock (seedling, MM.106, and M.7a) on fruit diameter of three cultivars ('Red Delicious', `Granny Smith', and `Gala') was studied over two growing seasons (1990-91) in the arid climate of Willcox, Ariz. Daily fruit growth rate (DFGR) and effective fruit growth period (EFGP) data indicate cultivar differences in DFGR as well as EFGP. Cultivars with a high DFGR had a relatively shorter EFGP. Rootstock had no significant effect on EFGP. Cultivar x rootstock interaction on fruit diameter was significant for DFGR, but not for EFGP. `Red Delicious' and `Granny Smith' trees produced larger fruits on MM.106 and M.7a than on seedling rootstock. For `Gala', there was no significant effect of all rootstock on fruit diameter.

Migration of nitrate to groundwater has become a serious threat in many agricultural areas. This paper presents the results of experimental laboratory tests studying the nitrate gradient developed in response to an electrical potential. Two systems were tested; the first had no flow (closed system) and the second had flow opposite to the direction of the electrical current. A solution of sodium nitrate in sandy soil was used in both systems. The tests showed that the electro-kinetic process effectively concentrated and retained nitrate close to the anode. The movement of NO 3 − through the soil column was significantly influenced by the development of a pH gradient. Statistical analysis was performed to determine best-fit equations relating the nitrate gradient to the electrical input and pH gradient. A simple one-dimensional finite difference model was used to predict the pH gradient developed during the electro-kinetic process. The experimental measurements closely agreed with the predicted spatial and temporal distribution of the nitrate gradient for both closed and open system configurations.

COMMERCIAL soil thermocouple psychrometers of both the single junction and double junction types were tested to evaluate the magnitude and significance of Joule and resistance heating on water potential deter-minations near saturation. For water potential deter-minations above about -4 bars a cooling current of 8 mA produced significant heating and yielded unreliable results for both probe types. A cooling current of 3 to 4 mA applied for 15 s provided reliable determinations of water potential up to about -0.5 bars when psychrometer output was read 6 s after cessation of cooling.

WASTEWATER was applied to three soils to deter-mine the sealing affect or change in hydraulic properties. Saturated conductivities of disturbed soils were measured weekly under laboratory conditions over a 40-wk period. For the Lester clay loam and Waukegan silt loam, saturated conductivities of the soils were less than the saturated conductivities of the wastewater seal. In Hubbard loamy sand, an immediate seal was formed due to the application of wastewater.

A one-dimensional, physically-based computer model was developed for predicting direct groundwater recharge. The model was verified using three years of data from an instrumented site in east central Minnesota. Although the processes of infiltration and redistribution during frozen soil periods were not modeled, the model is capable of operating during both frozen and nonfrozen soil periods. The model includes submodels for evapotranspiration, soil-water extraction, snowmelt, surface depressional storage, infiltration and redistribution. The model predicts water table level and soil moisture. Water extraction may also be modeled. The model predicted both water table elevations and soil moisture levels with reasonable accuracy over the three-year period modeled.

A soil-water model was developed and tested. The model provides satisfactory predictions of soil-water content at various depths for corn at a location in south-west Minnesota. The model was used to study the poten-tial effects of basin tillage on soil moisture levels at two locations, one in Minnesota and another in south central Texas. Results of these projections indicated that basin tillage increases soil moisture and decreases crop stress significantly as compared to conventional tillage by in-creasing infiltration of excess precipitation during the growing season, the off-season or both.

Development of a 2-stage, measured parameter, infiltration model is reviewed. The model has been verified against finite difference solutions of the unsaturated flow equation, by laboratory tests and has been evaluated under field conditions. Progress of recent research utilizing this model is discussed. Results of recent research indicate that the effects of air entrapment on hydraulic conductivity must be taken into account. A reasonable approach to this problem is to evaluate relative conductivity as a function of relative moisture content and use this relationship to evaluate hydraulic conductivity at field saturation. Additional factors which have been investigated include air viscous effects and the effects of tillage and surface sealing. While significant progress has been made toward including these effects in the model, additional research is required. An attractive attribute of the model is that all parameters utilized in the model are measurable and thus no parameter fitting is required. The paper discusses how parameters may be evaluated and how the model operates, and presents some examples of model predictions under different conditions of soil composition and rainfall pattern.

A modified Mein and Larson model was employed to predict time to surface ponding and corresponding volume of water infiltrated under two types of center pivot irrigation systems. Predictions were made for two soil types with differing surface cover. Results were com-pared with those observed in the field. The model did a good job of predicting time to surface ponding for the soil with a well protected surface. For a soil with in-complete cover, the prediction of both time to ponding and the corresponding volume was poor.

THREE physically based infiltration models are com-pared both in terms of theoretical development and performance. The models are an unmodified Green-Ampt-Mein-Larson (GAML-UNMOD) model, a similar model which was modified to account for entrapped air (GAML-ETA model) and a model which considers both air entrapment and air resistance effects (GAML-ART model). The GAML-UNMOD model is conceptually the simplest model but in all cases, this model failed to do a reasonable job of predicting time to surface ponding. This failure appears to be due primarily to use of un-modified saturated hydraulic conductivity values. The GAML-ETA model did a better job of predicting time to ponding on dry soils but greatly over-predicted infiltra-tion on wetter soils. The GAML-ART model did the best overall job of predicting infiltration but did tend to over-predict on wet soils. This over-prediction by all models on the wetter soils may be due in part to partial surface sealing during preceding dry runs.