Temporal variability in water quality of agricultural tailwaters: Implications for water quality monitoring

Accurate assessments of non-point source pollution and the associated evaluation of mitigation strategies depend on effective water quality monitoring programs. Intensive irrigation season water quality monitoring was conducted on three agricultural drains (6 h to daily sampling) along with analysis of decade long records from two larger agricultural drains (biweekly to monthly sampling) in the San Joaquin Valley, California. Analyses revealed significant temporal variability in concentrations of nutrients, salts, and turbidity over short time-scales (<1 day), as well as significant differences in monthly and annual mean concentrations. Statistical techniques were used to evaluate the sampling intensity required to meet rigorous confidence and accuracy criteria, as well as to evaluate the efficacy of different sampling strategies (e.g. grab samples versus composite samples). The number of samples required to determine mean constituent concentrations within 20% of the mean at a 95% confidence level ranged from 2 to 39 samples per month (SPM) for total phosphorus, 1-16 SPM for total nitrogen, 5-25 SPM for turbidity, and 1-3 SPM for electrical conductivity. Using a daily composite sample (4 subsamples per composite) instead of discrete samples was shown to maintain the same accuracy and confidence standards, while reducing the required sample number by up to 50%. This study emphasizes the value of a statistical approach for evaluating water quality monitoring strategies, and provides a framework through which cost-benefit analysis can be implemented in the development of monitoring plans.     

Sediment production and water quality of watersheds with contrasting land use in Navarre (Spain)

An experimental watershed (Oskotz principal- Op -ca.1700 ha) covered with forest and pasture (cattle-breeding) with an equally experimental sub-watershed (Oskotz woodland - Ow - ca. 500 ha) almost entirely under forest was continuously monitored during 8 years (2001-2008). These watersheds were established by the Government of Navarre (Spain) in order to assess the impact of agricultural activities on different region of Navarre. The first results regarding exported sediment, runoff, nitrate and phosphate are presented herein. These results are compared with those from two grain-sown watersheds previously reported by the authors, elsewhere.The same as in the grain-sown watersheds, most runoff, sediment, nitrate and phosphate yields in Oskotz were generated during winter, though most erosive rainfalls occurred during summer. In Ow, average sediment, nitrate and phosphate yields were approximately: 700, 22, 0.35 kg ha year⁻¹, respectively; for Op these figures were 550, 54 and 0.76 kg ha year⁻¹, respectively.However, total sediment and solute yields were different depending on the prevailing land use: cereal crops > forest > pasture. Sediment yields in the forest were strongly affected by the logging moment, when exported sediment rocketed.Nitrate concentration and yields were lower (and under the critical threshold) in the forested/pastured watersheds than those recorded in the two intensively cultivated watersheds. However, phosphate yields were dramatically higher (and over the critical threshold) in the former watersheds due to the prevailing soil conditions and to the fertilization of pasture, mainly with slurry.The present work, along with that similar one recently reported by the authors, is an unprecedented and relevant piece of research for the region.     

Economic impacts on farm households due to water reallocation in China's Chaobai watershed

Our study area in the Chaobai watershed, upstream of Miyun Reservoir, has been undergoing agricultural water transfers to downstream municipal uses in Beijing. We examine the impacts of water reallocation on crop production and farmers’ income and discuss issues relating to current compensation mechanisms. We use data from a survey of 349 farm households and their farm plots in the upper Chaobai watershed within Hebei province. Water reallocation from upstream to downstream areas has reduced agricultural water supply and the area irrigated. Regression results show that in plots deprived of irrigation, maize yields decrease by 21% and crop revenues decline by 32%. On average, losing irrigation on one hectare of cultivated land reduces net crop income by 2422 yuan. We examine compensation arrangements and social equity for the major policies implemented in the region and we identify gaps between current compensation levels and farmers’ income and production losses. The current compensation received by farmers is generally lower than the losses incurred due to reduced irrigation. A more appropriate compensation mechanism is called for in future water transfers.     

Simulation of land use impacts on groundwater levels and streamflow in a Virginia watershed

Increase in withdrawal and decrease in recharge of groundwater due to urbanization influences subsurface flow regimes. The overall objective of this study was to determine the impact of land development activities on the subsurface flow regime in the Upper Roanoke River Watershed (URRW). A regional groundwater model of the URRW was constructed using Modular Three-Dimensional Ground-Water Flow Model (MODFLOW) and calibrated for steady-state conditions. Then, eight land use management scenarios were simulated on the Back Creek (BC) subwatershed to assess the impacts of residential density, residential location, and land-cover on hydraulic head of groundwater and streamflow. The average recharge output from the Hydrological Simulation Program, FORTRAN (HSPF) simulation was used as the direct input to MODFLOW to take changes in land use into account in the BC watershed. Development of agriculture and forest areas with low-population density on larger area (low-density scenario), near the middle of the watershed (mid-section scenario), and with changes all open space to lawn (lawn scenario) had greatest overall impact on the BC watershed for both hydraulic head and streamflow among density, location, and land-cover scenarios, respectively. The simulated scenarios indicated that decreases in both hydraulic head and streamflow coincided with the increases in impervious land. The reductions in hydraulic head and streamflow were restricted to the subwatershed where land use changes occurred. The urbanization impacts on both surface and subsurface regimes were very local with 20.8 cm of maximum difference in local hydraulic head and 0.532% of maximum percent difference in local streamflow at lawn scenario while average corresponding values through BC watershed was 4.3 cm and 0.153%, respectively. Use of a fully distributed surface model in a dynamic manner was recommended to solve the inconsistencies in the spatial and temporal scale of surface and groundwater models. However, the proposed approach can be used as a management and planning tool for evaluating the local and overall impacts of land use management on the surface and subsurface flow regimes.     

Multiple use of water and water productivity of communal small dams in the Limpopo Basin, Zimbabwe

The history of dam construction in Zimbabwe dates back to the 1920s and since then over 7,000 small dams have been constructed countrywide. Small dams are multipurpose structures used for improving rural livelihoods. The multipurpose nature of these dams has largely gone unquantified in terms of importance of the uses to the community and influence of management practises. The current study made use of a questionnaire among small dam users, key informant interviews, secondary data and observation on four communal dams in the Limpopo basin to establish the uses, volume of water abstracted and water productivity for some uses and the interrelationship between various organisations and the community in the management of small dams. Uses on all dams in order of importance were livestock watering, domestic use, irrigation, fishing, brick making, and collection of reeds used for roofing. Livestock consume on average over 70% of water for consumptive uses. Water productivity in terms of yield per volume unit of water used ranged from 0.025 kg m^?3 for vegetables to 7,575 kg m^?3 for bricks, and monetary values per volume unit of water used were Z$ 389,434 m^?3 for brick making and Z$ 1,874 m^?3 for irrigation. Traditional leadership and the community are pivotal in the management of the small dams, with some organisations giving technical, financial and input assistance. The management and conservation of small dams needs to be well coordinated between the communities, NGOs and government if the full benefits of these national resources are to be realised in the long term.     

Seasonal variations in nitrate leaching in structured clay soils under mixed land use

Nitrate leaching was studied for 2 years in a structured clay soil (Evesham series) under grass, winter wheat and spring barley at N fertilizer inputs of 135–144 kg ha^?1 year^?1. Measurements of soil water to 2 m depth by neutron probe showed that the year could be divided into well defined periods of deficit, separated by a period when the soil was at its winter mean water content. Soil water potentials showed very little gradient for water flow below 1 m, and a persistent convergent zero flux plane at 40–60 cm depth during the autumn wetting-up period (September—November).Nitrate concentration in the drainage increased with discharge rates up to 3–6 mm day^?1. Mean nitrate concentrations were generally highest during intermittent drain-flow in the autumn. Of the total N leached over the 2 years, 23 to 28% (5–7 kg N ha^?1) was lost during this period. The remainder (13–25 kg N ha^?1) was leached during winter and virtually no N was lost in the following spring-early summer. This seasonal pattern of N leaching was interpreted in terms of intermittent flow during rainfall of nitrate-rich water from surface layers, which bypassed the relatively dry soil matrix at 40–60 cm, but was intercepted by natural and artificial drainage channels. Implications for the prediction of N leaching loss based on the concept of excess winter rainfall are discussed. When predicting the start of N leaching in structured clay soils, the soil water status should be assessed from measurements of water potential rather than water content.     

鞍山地下供水水源地水质现状评价探析

随着社会经济的发展和人口的不断增加,饮用水的污染已逐渐从地表水渗透到地下水之中,近年来,随着工业化进程的逐渐加快以及农业活动的频繁,许多地区的地下水污染物呈现多样性和复杂的特点,为此,保证地下水水源地安全就显得尤为重要.本文对鞍山市地下水质现状进行初步评价,旨在为治理地下水水质污染提供依据.     

Seasonal and land use impacts on the nitrate budget and export of a mesoscale catchment in Southern Portugal

Stream nitrate nitrogen exports are an important indicator of agricultural impacts on aquatic health in catchments. Quantitative assessment of factors and processes affecting stream nitrate loadings is complex because of the large number of causal factors and processes, such as weather and rainfall, catchment hydrological behavior, soils, land use practices and biogeochemical processes. An eco-hydrological catchment modeling approach, using the SWAT model driven by detailed field data, was used to analyze the nitrate export and the components of the nitrogen budget of the 352 km² upper Roxo river catchment in Southern Portugal. A detailed eight-year record (2001–2008) of the monitoring of weather, reservoir inflow, stream biogeochemistry, soils, in-stream and groundwater quality, and fertilizer application was used to calibrate and validate the streamflow and nitrate loadings obtained by the model. Results indicated a strong seasonal variation in nitrate exports, closely related to temperature and rainfall. Monthly nitrate loadings varied from 0.02 to 2.48 kg N ha⁻¹ during summer and between 0.03 and 14 kg N ha⁻¹ during late autumn and winter. Stream nitrate values, ranging from 1.5 to 16.5 mg N L⁻¹, were strongly related to extreme rainfall occurrences and wet periods. Detailed analysis of nitrate budget components at the sub-catchment level enabled evaluation of the impacts of the various processes affecting the nitrate nitrogen pool of the catchment. Besides high fertilizer inputs for annual crops, it was shown that biological nitrogen fixation and wet deposition by rainfall should be accounted for in input balances. Where denitrification naturally reduces nitrate levels in soils, streams and the reservoir, the largest contribution to stream nitrate originates from leached soil nitrate reappearing in groundwater baseflow, compared with less than 2% from direct surface runoff during high rainfall events. A fertilizer reduction scenario was effectively implemented to evaluate remedial nitrate control policies in accordance with the European Nitrate and Water Framework Directives. Agricultural practices and seasonal weather fluctuations were the main reasons for temporal variations in nitrate export via small streams to the main reservoir.     

不同土地利用条件下土壤质量综合评价方法

针对传统的土壤质量评价方法难以满足现代农业发展的现状,提出了一种土壤质量指数法(SQI)综合评价土壤质量,旨在为农业生产、农产品产地选址、农业环境保护等提供理论支撑和参考依据。将方法在北京市郊区7种土地利用方式（粮田、林地、湿地、荒地、果园、菜地、草地）上进行了应用,并与常规方法进行了对比,结果表明：采用隶属度模型评价土壤肥力,肥力高低顺序为：湿地＞菜地＞粮田＞林地＞果园＞荒地＞草地;采用内梅罗污染指数评价了重金属污染状况,污染程度高低顺序为：湿地＞菜地＞荒地＞果园＞林地＞粮田＞草地;采用SQI指数评价土壤综合质量,其综合质量的高低顺序为：湿地＞粮田＞菜地＞果园＞林地＞荒地＞草地。此外还对评价模型的适用范围、评价结果的划分等一系列关键问题进行了探讨,得出：SQI指数评价方法的应用及结果的划分涵盖了不同的土地利用方式的农用地,体现了各种土壤属性的差异和变异特性,评价结果可实现土壤综合质量定性和定量化,能够反映土壤的关键信息,符合农业生产需要。     

Boots on the ground: construction management of urbanizing irrigated farm land

Since its inception, in 1885 the Buckeye Irrigation Canal has delivered irrigation water in the Buckeye Valley, southwest of Phoenix, Arizona. Throughout its tenure the owners of the canal have consulted design professionals for its engineering needs. Early engineering in 1885 established canal alignments, delivery points and channel capacity. Until recently, the Buckeye Valley was a rural area relying on agricultural revenues to drive the local economy. Now, due to the recent housing market boom new homes started springing up like corn in September driving the existing open-channel laterals below grade into a patch work redesigned pipeline system. Because of these changes, professional construction managers are an enormous benefit to the Buckeye Water Conservation and Drainage District (BWCDD), the owner of the canal.As a result of this urbanization, contractors working for home developers are installing irrigation pipelines and systems with the focus of completing the project as quickly and economically as possible. Irrigation providers, on the other hand, focus on meeting the agricultural needs of their clients with consistent and uninterrupted water delivery. The services of a professional construction manager help both entities achieve their respective goals, shield BWCDD from construction of sub-par systems and risk, maintain uninterrupted service to growers and providing the technical expertise to communicate with both BWCDD and contractors.Construction managers provide a number of services to rural irrigation districts under-going urbanization. They team with an irrigation district by:

• Understanding irrigation design concepts;
• Understanding agricultural demands;
• Providing a thorough knowledge of construction practices and standards;
• Creating long-term design functionality;
• Reducing stress on and increasing productivity of personnel;
• Coordinating construction activities with water deliveries;
• Verifying constructed facilities perform as designed, which reduces maintenance costs.

Construction managers represent an irrigation district in the field by:

• Reviewing development plans for adherence to current construction standards and practices and coordinates construction schedules with water delivery needs;
• Observing construction for proper installation;
• Clarifying installers understanding of plans and specifications;
• Coordinating interruptions in service;
• Tracking multiple construction projects;
• Explaining agricultural practices to contractor personnel;
• Providing a single point of contact for construction related correspondence.

These “boots on the ground” create a local presence with a focus on the specific needs unique to an irrigation district. They provide a liaison while minimizing the impact to its growers.This paper will discuss the strain of urbanization on an irrigation district and the benefits of an engineering consulting firm to manage construction projects. The benefits include expertise, technical resources, design capability, coordination and inspection. Construction managers can help protect an irrigation district from being overwhelmed by rapid urbanization.     

Changing water allocations and land use and the design of small scale irrigations schemes

In an earlier article in this journal Robert Hecht argued that in the design of small scale irrigation systems a study of the existing land and water rights is essential. This paper suggest that a study of existing land and water rights alone does not suffice, but that the intended changes in water availability have to be taken into account as well. Using examples from a small-scale irrigation project in Balochistan (Pakistan), the paper discusses four categories of changes in water availability, i.e. new development: major increase in available water; marginal increase in available water and integration of independent systems. Each one of these categories has a different impact in terms of changes in land and water rights, changes in the water distribution system and selection of command area. To accomodate these changes close consultation with the water users is required during the development of the scheme, and designs will often evolve incrementally.     

Water balance and water use efficiency of different land uses in western Himalayan valley region

Various land uses, including sole plantations of leucaena and eucalyptus, maize–wheat, chrysopogon grass or turmeric and their tree crop mixtures were compared for period of nine years in two sequences for runoff, water use and water use efficiency on nine large erosion plots on 4% slope. Availability of water during summers and climatic evaporative (EP) demand during winters appear to be the governing factors for seasonal water use. About 70% of annual water consumption occurs during the four months (July to October) of rainy season. During this season water use was about 3–4 times to EP for trees and grass and 2.5 times for maize. The water use equals EP regardless the land use during winter season, while it reduced to about one-third to half of EP in the summer season. Annual water use is found to be closely linked with runoff reduction efficiency of the land use. Sole plantations of leucaena and eucalyptus showed negligible runoff losses and their water use approximated annual rainfall. Agroforestry land uses also reduced runoff and increased water use and water use efficiency. Seasonal crops exploited 1.5 m depth of profile more exhaustively than trees, whereas trees used soil water down to 3.0 m depth. Therefore, in tree crop mixtures more efficient soil water use was observed as compared to monocropping systems. Results of this study indicate that water conserved under sole tree plantations and due to tree intervention in agroforestry land uses through runoff reduction, is utilised to meet increased evapotranspiration demand, and hence ground water recharge in appreciable quantities is unlikely.     

Managing water by managing land: Addressing land degradation to improve water productivity and rural livelihoods

The premise of this paper is that the key to effective water resources management is understanding that the water cycle and land management are inextricably linked: that every land use decision is a water use decision. Gains in agricultural water productivity, therefore, will only be obtained alongside improvements in land use management. Expected increases in food demands by 2050 insist that agricultural production - and agricultural water use - must increase. At the same time, competition for water between agricultural and urban sectors will also increase; and the problem is further compounded by land degradation. A global survey suggests that 40% of agricultural land is already degraded to the point that yields are greatly reduced, and a further 9% is degraded to the point that it cannot be reclaimed for productive use by farm level measures. Soil erosion, nutrient depletion and other forms of land degradation reduce water productivity and affect water availability, quality, and storage. Reversing these trends entails tackling the underlying social, economic, political and institutional drivers of unsustainable land use. This paper is based on a review of global experiences, and its recommendations for improving water management by addressing land degradation include focusing on small scale agriculture; investing in rehabilitating degraded land to increase water productivity; and enhancing the multifunctionality of agricultural landscapes. These options can improve water management and water productivity, while also improving the livelihoods of the rural poor.     

水肥耦合对温室番茄产量、水分利用效率和品质的影响

为指导日光温室番茄高产节水优质的灌溉施肥,以番茄为研究对象,设置3种施肥方式(总施肥量相同,施肥时间不同,其中F₁:不施底肥,番茄移栽后随水追施总肥量的30%,剩余70%平分6次追肥,F₂:底肥施1/2,剩余平分6次追肥,F₃:全施底肥不追肥)和3种土壤水势的灌水下限(W₁:-30 kPa,W₂:-50 kPa,W₃:-70 kPa),研究滴灌条件下水肥耦合对番茄耗水量、产量、水分利用效率和品质的影响.结果表明:施肥方式对番茄的耗水量差异不具有统计学意义,而灌水下限对耗水量有极显著性影响,且耗水量与灌水量呈极显著的正相关关系(P<0.01);与产量最大处理F₂W₁相比,F₂W₂处理产量降低6.91%,但节水14.83%,水分利用效率提高8.51%;TTS质量分数与平均单果重呈极显著负相关,而与除糖酸比外其他影响品质指标呈显著性正相关关系;综合考虑产量、WUE及TTS质量分数,利用TOPSIS综合评价方法,确定了温室滴灌条件下番茄节水调质的最优灌溉施肥模式为:移栽前施入底肥为总肥量的50%,移栽后灌水20 mm,进入开花坐果期以后,20 cm土层的土壤水势控制在-50 kPa以上,每次灌水定额为10 mm,剩余肥料每隔1次灌水追肥1次,将剩余50%的肥料分6次追肥.研究成果为制定日光温室番茄节水高产优质的灌溉模式提供了理论依据.     

Controlling nitrogen release from farm ponds with a subsurface outflow device: Implications for improved water quality in receiving streams

The retention of nutrients in farm ponds has many potential benefits, including reduction of nitrogen and phosphorus (promoters of eutrophication) in receiving streams. The aim of this study was to evaluate the efficacy of a commercial subsurface pond outflow control device (Pond Management System™) on nutrient retention in farm ponds. Four ponds of similar size and water chemistry in the upper Tar River basin of North Carolina, USA were studied; three were equipped with the pond outflow control device and one was retained without a device (normal surface outflow) that served as a reference site. Water samples were collected monthly from each pond at 0.3 m intervals from the surface to 2.1 m at a fixed station adjacent to the pond standpipe and from the pond outflow pipe from March to October 2005. The water samples were analyzed for total Kjeldahl nitrogen (N), total phosphorus (P), chlorophyll a, and a suite of other physicochemical variables. In ponds with the subsurface outflow device, the mean N concentrations in the outflow were substantially less (6.2–20.7%) than concentrations at the pond surface. Concentrations of N in the outflow were similar to N concentrations at intermediate pond depths (0.9–1.5 m), the depth of the outflow devices, indicating water was drawn from these depths and that N was being retained in the surface layers of the pond. Also, mean water temperatures were 1.1–1.9 °C cooler at intermediate depths compared to the surface, suggesting potential application of the outflow device for minimizing warm water outflows to receiving streams. These results provide evidence that under these conditions a subsurface pond outflow device can reduce nutrient release to receiving streams, thereby increasing overall stream water quality.     

Analysis on groundwater table drawdown by land use and the quest for sustainable water use in the Hebei Plain in China

Increased water use in the Hebei Plain during the last decades has caused serious groundwater level decline and many geological problems which have become the biggest threat to social–economic sustainability. Thus, to determine the factors resulting in the groundwater decline and to develop a practical plan for long-term groundwater use appear to be necessary in this region. In this paper, a water balance model is used in conjunction with regression techniques to estimate the groundwater recharge coefficient and the specific yield (defined as the ratio of the volume of water that a saturated rock or soil will release by gravity drainage to the volume of rock or soil) and the groundwater withdrawn by different water use sectors and the corresponding drop in the water-table are analyzed. The decline in water-table by different crops and water economic benefit of crops are discussed in detail in order to suggest sustainable use of groundwater resources in the Hebei Plain. Finally, sample policy scenarios are developed to show how groundwater in the Hebei Plain could be used in a sustainable manner. In our study, it is found that agriculture is the major consumer of groundwater, with about 85% of the total groundwater withdrawals, and groundwater depletion is mainly caused by agricultural water use. Production of winter wheat exerts a great negative influence on the groundwater system. Winter wheat is the most water consuming crop and result in significant decline of groundwater table. Water economic benefit of winter wheat is lower than that of other crops and withdrawing winter wheat sown area is rational option to make sustainable use of groundwater. With far-sighted and regional planning, the limited water resource can be used sustainably to generate maximum social benefits. This paper will provide information necessary for land-use planning in a severe water shortage region where farmland is mainly irrigated by groundwater.     

Water saving and economic impacts of land leveling: the case study of cotton production in Tajikistan

Water conservation is essential to prevent salinity and land degradation in Central Asia. Therefore, field-testing and evaluation of water conservation methods, i.e. laser land leveling in new farming systems of Central Asia is important task. This in mind the International Water Management Institute (IWMI) and its regional partner on IWRM FV (IWRM FV project – Integrated Water Resources Management in Ferghana Valley project is funded by Swiss Development Cooperation (SDC) and conducted jointly with IWMI and Scientific Information Center of Interstate Coordination Water Commission (SIC ICWC) in the Ferghana Valley of Central Asia) project SIC ICWC have conducted 3 year study of impacts of the Laser leveled land leveling on water use, productivity and crop yields in northern Tajikistan. The major research question was laser land leveling an effective water saving tool in the new context of land use and ownership on smaller private plots. Can farmers afford the costs of laser land leveling and how economically viable is it? These research questions were studied in 5 ha laser leveled and neighboring non-leveled (control) fields for 2004–2006. The results showed that laser land leveling can reduce the water application rate in 2004 by 593 M³/ha, in 2005 by 1509 M³/ha and in 2006 by 333 M³/ha in comparison with the unleveled field, located in the similar agro-ecological conditions. The deep percolation was 8% lower and run off 24% less than in non-leveled field. The average annual net income from the laser field was 22% higher than that from the control field. The gross margin from the laser-leveled field were 16. 88 and 171% higher compared to that from the control field for 2004, 2005 and 2006, and on average was 92% higher. In spite of these positive results, there are hindrances on wide application of laser land leveling in Tajikistan. These are absence of initial capital of farmers and scattered land location.     

Evaluation of the influence of irrigation methods and water quality on sugar beet yield and water use efficiency

Rapid urbanization and industrialization have increased the pressure on limited existing fresh water to meet the growing needs for food production. Two immediate responses to this challenge are the efficient use of irrigation technology and the use of alternative sources of water. Drip irrigation methods may play an important role in efficient use of water but there is still limited information on their use on sugar beet crops in arid countries such as Iran. An experiment was conducted to evaluate the effects of irrigation method and water quality on sugar beet yield, percentage of sugar content and irrigation water use efficiency (IWUE). The irrigation methods investigated were subsurface drip, surface drip and furrow irrigation. The two waters used were treated municipal effluent (EC = 1.52 dS m⁻¹) and fresh water (EC = 0.509 dS m⁻¹). The experiments used a split plot design and were undertaken over two consecutive growing seasons in Southern Iran. Statistical testing indicated that the irrigation method and water quality had a significant effect (at the 1% level) on sugar beet root yield, sugar yield, and IWUE. The highest root yield (79.7 Mg ha⁻¹) was obtained using surface drip irrigation and effluent and the lowest root yield (41.4 Mg ha⁻¹) was obtained using furrow irrigation and fresh water. The highest IWUE in root yield production (9 kg m⁻³) was obtained using surface drip irrigation with effluent and the lowest value (3.8 kg m⁻³) was obtained using furrow irrigation with fresh water. The highest IWUE of 1.26 kg m⁻³ for sugar was obtained using surface drip irrigation. The corresponding efficiency using effluent was 1.14 kg m⁻³. Irrigation with effluent led to an increase in the net sugar yield due to an increase in the sugar beet root yield. However, there was a slight reduction in the percentage sugar content in the plants. This study also showed that soil water and root depth monitoring can be used in irrigation scheduling to avoid water stress. Such monitoring techniques can also save considerable volumes of irrigation water and can increase yield.     

Identifying and controlling critical sources of farm phosphorus imbalances for Vermont dairy farms

Lake Champlain, located between Vermont, New York, and Quebec exhibits eutrophication mainly due to continuing phosphorus (P) losses from upstream nonpoint source areas. Several state and local agencies have initiated efforts aimed at assessing and identifying critical sources areas for P loss. To augment these efforts, accounting of farm P inputs (in purchased animal feed and fertilizers) and P outputs (in milk, meat, or off-farm sales of harvested crops or other products) is needed as a means of determining potential P build-up in farm soils. When farm P inputs exceed P outputs, P surplus occurs on the farm. This leads to potential soil-P accumulations and risk of P loss in runoff, negatively impacting the quality of receiving water bodies. In this study, a combination of farm record data and a model-based approach, using the Integrated Farming System Model (IFSM), was used to estimate farm P inputs and outputs, identify root causes of farm P imbalances, and explore viable P balancing strategies. Three Vermont dairy farms with varying farm systems (grass-based organic farm, fully confined farm, and a mixed system farm with high-producing confined dairy cows and grazing heifers) were studied. These farms were found to have P surpluses ranging from 5.5 kg/ha to 18.7 kg/ha on annual basis. This study also identified critical causes of P imbalances for each farm and suggested farm specific alternative strategies needed to address the P imbalances. By balancing farm P inputs and outputs, potential accumulation of soil-P can be prevented. As a result, maximum benefits can be obtained from land treatment measures implemented to control off-field P loss without the additional concern of continuing P build-up that could reduce their effectiveness.     

Evaporative water use of different land uses in the upper-Thukela river basin assessed from satellite imagery

Evaporative water use of various land use classes in the upper-Thukela river basin was estimated using the public domain version of the Surface Energy Balance Algorithm for Land (SEBAL) and Moderate Resolution Imaging Spectroradiometer (MODIS) satellite images. Twenty eight images were analyzed covering the period between June 2005 and September 2006. The South Africa land use map developed in the year 2000 was used to compute the evaporative water use of the various land uses in 13 Quaternary Catchments (QCs) in the upper-Thukela river basin.There was a good correlation between the SEBAL estimates of total evaporation and ground measurements from a Large Aperture Scintillometer installed at a site in one of the QCs in the study area. It was observed that the land uses that generated relatively large volumes of evaporative water were forestry (i.e. Eucalyptus, Pine, mixed species & indigenous), “water bodies” (i.e. water supply reservoirs, farm reservoirs) and wetlands. Total evaporation rates for all land use classes were high during the summer season (wet), with Eucalyptus ranging between 3 mm d⁻¹ during the winter season (dry) and about 5 mm d⁻¹ during the summer season. Bare rocks and eroded soil surface land use class had the least evaporative water use i.e., less than 1 mm d⁻¹. The relatively low evaporation rates over “water bodies” during the dry winter season could be attributed to the averaging of mixed pixels (wet and dry) due to change in areal coverage and which could not be captured in the 1 km × 1 km low resolution MODIS images. Thus, the potential for applying remote sensing techniques, using low resolution satellite images, to quantify water use by various land uses in the Thukela river basin was explored with promising results.