An artificial capillary barrier to improve root zone conditions for horticultural crops: physical effects on water content

Capillary barriers (CBs) occur at the interface of two soil layers having distinct differences in textural and hydraulic characteristics. The objective of this study was to introduce an artificial CB, created by a layer of gravel below the root zone substrate, in order to optimize conditions for the cultivation of horticultural crops. Potential root zone formats were analyzed with and without the gravel CBs for variables including the following: depth of CB; barrier separating the root zone from the surrounding soil; and root zone soil texture. Field and simulated results revealed that artificial CBs increased root zone water content and changed water flow dynamics. Volumetric soil water content was increased by 20–70%, depending on the soil texture and depth of the barrier. Sandy soil texture and shallower placement resulted in relatively higher water content. For sandy soil without plants, a shallow (0.2 m depth) CB increased water content of the overlaying soil by 50% compared to the control. The introduction of a gravel CB below the root zone of pepper plants (Capsicum Annum L.) lead to 34% higher matric head, 50% lower diurnal fluctuations in matric head and 40% increase in pepper fruit yield. Increasing water content by way of artificial CBs appeared to improve the water use efficiency of pepper plants. Such an improvement could lead to reduced water and fertilizer application rates and subsequent reduction in contamination below the root zone. This is especially relevant for substrates of low water-holding capacity typically used in horticulture crop production.     

VegSyst, a simulation model of daily crop growth, nitrogen uptake and evapotranspiration for pepper crops for use in an on-farm decision support system

The VegSyst simulation model was developed to assist with N and irrigation management of sweet pepper grown in plastic greenhouses in the Mediterranean Basin. The model was developed for use in an on-farm decision support system with the requirement for readily available input data. Dry matter production (DMP), crop N uptake and crop evapotranspiration (ET_c) are simulated on a daily basis. DMP is calculated from daily fraction of intercepted photosynthetically active radiation (PAR), PAR radiation, and radiation-use efficiency. Fraction of intercepted PAR is calculated from relative thermal time. Crop N uptake is calculated as the product of DMP and N content which is described by a power function of DMP. ET_c is the product of daily reference evapotranspiration (ET_o) using an adapted Penman–Monteith equation, and a daily simulated crop coefficient value. The VegSyst model for soil-grown, greenhouse pepper was calibrated in one crop and validated in three different crops. In the validation, the model accurately simulated crop growth, N uptake and ET_c. Relative to measured values, simulated DMP at final harvest was 0.89–1.06, and crop N uptake was 0.97–1.13. Simulated cumulative ET_c for complete crops was 0.95–1.05 of measured values.     

Determination of comprehensive quality index for tomato and its response to different irrigation treatments

In order to investigate better irrigation scheduling with the compromise between yield and quality of greenhouse-grown tomato under limit water supply, two experiments of different irrigation treatments were conducted in the arid region of northwest China during spring to summer in 2008 (2008 season) and winter in 2008 to summer in 2009 (2008-2009 season). After measuring single quality attributes, the analysis hierarchy process (AHP) and technique for order preference by similarity to an ideal solution (TOPSIS) were used to determine the weight of single quality attributes and comprehensive quality index, respectively. The results show that the rank of comprehensive quality index had good fitness to that of single quality attributes, indicating that the comprehensive quality index was reliable. Compared to full irrigation, applying 1/3 or 2/3 of full irrigation amount at the seedling stage had slight improvement of comprehensive quality and limit water saving. Applying 1/3 or 2/3 of full irrigation amount at the fruit maturation and harvesting stage decreased the yield by 23.0-40.9%, but had the best comprehensive quality. However, applying 1/3 of full irrigation amount at the flowering and fruit development stage significantly reduced crop water consumption and had obvious improvement of comprehensive quality, but did not decrease the yield significantly and water use efficiency in the 2008 season. And applying 2/3 of full irrigation amount at the flowering and fruit development stage significantly decreased crop water consumption and slightly improved the comprehensive quality, but did not decrease the yield significantly in the 2008-2009 season. Considering the water saving amount, yield and comprehensive quality, applying 1/3 or 2/3 of full irrigation amount at the flowering and fruit development stage and no water stress in other growth stages appears to be a better irrigation scheduling with the compromise between yield and quality of greenhouse-grown tomato, which can be recommended for the spring to summer and winter to summer seasons in the arid region of northwest China.     

Sprinkling-induced foliar injury to pepper plants: Effects of irrigation frequency,duration and water composition

Summary This study was conducted to determine the conditions and causes of foliar salt absorption and injury from sprinkler irrigation with saline water. Bell pepper plants (Capsicum annuum L. cv. Yolo Wonder B) grown in covered nutrient solution cultures in the greenhouse were sprinkled daily with NaCl and CaCl₂ waters for up to 10 weeks. Unsprinkled plants grown in nonsaline, and in one experiment, saline cultures were compared with plants sprinkled with waters containing different concentrations of NaCl and/or CaCl₂. Both the frequency and duration of sprinkling (up to 32 min each day) were tested.The results showed that Ca²⁺, Na⁺, and Cl^– were readily absorbed through the leaves at rates that were essentially linear functions of salt concentration and duration of sprinkling. Increasing frequency of sprinkling increased salt uptake and injury more than increasing duration. Sprinkling with either NaCl or CaCl₂ waters was more toxic to pepper than mixtures of the two salts. Although CaCl₂ was more toxic than NaCl, low concentrations of Ca²⁺ ameliorated the detrimental effects of NaCl waters. Foliar analyses indicated that leaf injury was not correlated with Cl^– accumulation. It appeared that it was caused directly by excessive cation accumulation or indirectly by the resultant ionic imbalance.Received for publicationSupervisory Plant Physiologist, Chemist, and Research Agronomist     

Fresh tomato production for the Sydney market: An evaluation of options to reduce freshwater scarcity from agricultural water use

In response to the growing concerns of freshwater scarcity, two metrics are considered for assessing the impacts of consumptive water use of a kg of fresh tomato supplied to the Sydney market. The first is the water use efficiency (WUE)—commonly used by agronomists which considers the absolute volumes of water consumed, and second, a recently developed method for water footprints based on Life Cycle Assessment (LCA) which describes the impacts in terms of contributing to freshwater scarcity. The results indicated that although a kg of tomato supplied from within Sydney had the highest water use efficiency (38 L for a kg of tomato as compared to 39-78 L from other regions of Australia), it had the biggest LCA-based water footprint (16 L for a kg of tomato as compared to 1.9-2.2 L from other regions of Australia). WUE as an indicator of agriculture water use is inappropriate to indicate the potential to contribute to local freshwater scarcity; potential stress on local and regional water resources, estimated using LCA-based water footprints, provide useful dimension to assess consumptive water use. Having both metrics will enable to achieve short term benefits at the farm level for saving water (through water use efficiency), while also recognising that longer term changes are required for alleviating freshwater scarcity (through LCA-based water footprints). Scenario modelling indicated relocation of production away from Sydney or modernisation of Sydney tomato greenhouse industry as a priority for reducing freshwater scarcity. The latter may be the best long term option to reduce additional emissions from transport and to take advantage of recycled water sources from Sydney's wastewater.     

A model of crop yield response to irrigation water salinity: theory,testing and application

A relationship between crop yield and irrigation water salinity is developed. The relationship can be used as a production function to quantify the economic ramifications of practices which increase irrigation water salinity, such as disposal of surface and sub-surface saline drainage waters into the irrigation water supply system. Guidelines for the acceptable level of irrigation water salinity in a region can then be established. The model can also be used to determine crop suitability for an irrigation region, if irrigation water salinity is high. Where experimental work is required to determine crop yield response to irrigation water salinity, the model can be used as a first estimate of the response function. The most appropriate experimental treatments can then be allocated. The model adequately predicted crop response to water salinity, when compared with experimental data.Abbreviations A Crop threshold rootzone salinity in Equation of Maas and Hoffman (dS/m) - B Fractional yield reduction per unit rootzone salinity increase (dS/m)^–1 - C_i Average salinity of applied water (dS/m) - C_r Average salinity of rainfall (dS/m) - C_s Linearly averaged soil solution salinity in the rootzone (dS/m) - C_se Linearly averaged soil saturation extract salinity in the rootzone (dS/m) - C_w Average salinity of irrigation supply water (dS/m) - C_z Soil solution salinity at the base of the crop rootzone (dS/m) - C Mean root water uptake weighted soil salinity in equation of Bernstein and François (1973) (dS/m) - E_p Depth of class A pan evaporation during the growing season (m) - ET_a Actual crop evapotranspiration during the growing season (m) - ET_m Maximum crop evapotranspiration during the growing season (m) - I The total depth of water applied during the growing season (including irrigation water and rainfall) (m) - K Empirical coefficient in leaching equation of Rhoades (1974) - K_c Crop coefficient for equation of Doorenbos and Pruit (1977) to estimate crop water use - K_y Yield response factor in equation of Doorenbos and Kassam (1974) - LF The leaching fraction - Ro Depth of rainfall runoff during the growing season (m) - R Depth of rainfall during the growing season (m) - W Depth of irrigation water applied during the growing season (m) - Y Relative crop yield - Y_a Actual crop yield (kg) - Y_m Maximum crop yield (kg) - /z Dimensionless depth for equation of Raats (1974), and empirical coefficient for the leaching equation of Hoffman and van Genutchen (1983)     

FSSIM, a bio-economic farm model for simulating the response of EU farming systems to agricultural and environmental policies

The disciplinary nature of most existing farm models as well as the issue specific orientation of most of the studies in agricultural systems research are main reasons for the limited use and re-use of bio-economic modelling for the ex-ante integrated assessment of policy decisions. The objective of this article is to present a bio-economic farm model that is generic and re-usable for different bio-physical and socio-economic contexts, facilitating the linking of micro and macro analysis or to provide detailed analysis of farming systems in a specific region. Model use is illustrated in this paper with an analysis of the impacts of the CAP reform of 2003 for arable and livestock farms in a context of market liberalization. Results from the application of the model to representative farms in Flevoland (the Netherlands) and Midi-Pyrenees (France) shows that CAP reform 2003 under market liberalization will cause substantial substitution of root crops and durum wheat by vegetables and oilseed crops. Much of the set-aside area will be put into production intensifying the existing farming systems. Abolishment of the milk quota system will cause an increase of the average herd size. The average total gross margin of farm types in Flevoland decreases while the average total gross margin of farms in Midi-Pyrenees increases. The results show that the model can simulate arable and livestock farm types of two regions different from a bio-physical and socio-economic point of view and it can deal with a variety of policy instruments. The examples show that the model can be (re-)used as a basis for future research and as a comprehensive tool for future policy analysis.     

Investing in water for food, ecosystems, and livelihoods: An overview of the comprehensive assessment of water management in agriculture

The authors of the recently completed Comprehensive Assessment of Water Management in Agriculture (CA) concluded that there are sufficient water resources to produce food for a growing population but that trends in consumption, production and environmental patterns, if continued, will lead to water crises in many parts of the world. Only if we act to improve water use will we meet the acute fresh water challenge. Recent spikes in food prices, partially caused by the increasing demand for agricultural products in non-food uses, underline the urgent need to invest in agricultural production, of which water management is a crucial part. The world experienced similar pressure on per capita food supplies and food prices in the 1960s and 1970s, but the challenges now are different than those we experienced 50 years ago. The world's population is substantially larger, there are many more people living in poverty, and the costs of many agricultural inputs are much higher. The current situation and the long-term outlook require a fresh look at approaches that combine different elements such as the importance of access to water for the poor, providing multiple ecosystem services, rainwater management, adapting irrigation to new needs, enhancing water productivity, and promoting the use of low-quality water in agriculture. This special issue highlights the analysis behind a number of policy options identified by the CA, a five-year multi-disciplinary research program involving 700 scientists. This introductory article sets the background and context of this special issue, introduces the key recommendations from the CA and summarizes the papers in this issue.     

基于图像处理和蚁群优化的形状特征选择与杂草识别

利用叶片形状特征区分杂草和作物是杂草识别的一个重要方法。为了提高杂草识别的精度和效率,通过形态学运算和基于距离变换的阈值分割方法分离交叠叶片,从单个叶片中提取包括几何特征和矩特征的17个形状特征,用蚁群优化（ACO）算法和支持向量机（SVM）分类器进行特征选择和分类识别,选取有利于分类的较优特征并实现特征的优化组合。棉田杂草试验结果表明,该方法能实现分类特征的有效缩减,经优化组合得到的最优特征子集用于杂草识别的准确率达95%以上,识别率高,稳定性好,对识别杂草时如何兼顾准确率和实时性具有参考意义。     

Determination of spatial water requirements at county and regional levels using crop models and GIS: An example for the State of Parana,Brazil

Due to the competitive use of available water resources, it has become important to define appropriate strategies for planning and management of irrigated farmland. To achieve effective planning, accurate information is needed for crop water use requirements, irrigation withdrawals, runoff and nitrate leaching as a function of crop, soil type and weather conditions at a regional level. Interfacing crop models with a geographic information system (GIS) extends the capabilities of the crop models to a regional level. The objective of this study was to determine the irrigation requirements, annual runoff and annual nitrate leaching for the most important crops of the Tibagi river basin in the State of Parana, Brazil. The computer tool selected for this study was the Decision Support System for Agrotechnology Transfer (DSSAT) version 3.5 (98.0) and its associated crop modeling and spatial application system AEGIS/WIN. It was assumed that farms within the same county use similar management practices. To achieve representative estimates of irrigation requirements, the weather data from stations located within each county or the nearest weather station were used. A weighting factor based on the proportion of soil type and crop acreage was applied to determine total annual irrigation withdrawals, annual runoff and nitrate leaching for each county in the river basin. The model predicted outputs, including yield, irrigation requirements, runoff and nitrate leached for different soil types in each county, were analyzed, using spatial analysis methods. This allowed for the display of thematic maps for irrigation requirements, annual runoff and nitrate leaching, and to relate this information with irrigation management and planning. The maximum annual irrigation withdrawal, runoff and nitrate leaching were 22,969 m³ per year, 31,152 m³ per year and 1488 t N per year in the Tibagi river basin. This study showed that crop simulation models linked to GIS can be an effective planning tool to help determine irrigation requirements for river basins and large watersheds.     

Simulated comparisons of breeding plans for beef production—Part 2: Hereford,angus and Charolais sires bred to Hereford,Angus and Hereford-Angus dams to produce feeder calves

Breeding plans using Hereford, Angus and Charolais sires mated to Hereford, Angus and Hereford-Angus dams were simulated. All breeding plans were considered in combination with a culling policy of culling a cow only if she failed to produce a calf for two consecutive years. The criterion of productivity was kilogrammes of calf produced per cow bred. Productivity of a herd was influenced by the age structure of the herd, since cow fertility, cow and calf mortality and preweaning growth of the calf were determined by the age of the cow, as well as by the genotypes of the cow and calf.For herds with purchased replacement heifers, the three-breed static crosses using Charolais sires were the most productive. The Hereford-Angus criss-cross ranked second, followed by the two-breed static crosses. The two-breed static crosses using Hereford or Angus sires were more productive than the two-breed crosses using Charolais sires. The straightbreds were the least productive. For herds producing their own replacement heifers, producing the replacements from the younger cows increased the kilogrammes of calf produced per cow bred by 2·7% in the Charolais-Angus static cross and 2·8% in the Charolais-Hereford cross.     

Visits to the U.S. Bureau of Reclamation from South Asia and the Middle East, 1946–1990: An indicator of changing international programs and politics

International study programs have contributed to the diffusion of modern irrigation technologies, approaches, and problems. But the patterns and processes of international travel have received little attention to date. This paper examines foreign visits to the US Bureau of Reclamation (USBR) from South Asia and the Middle East from 1946 to 1990. Using data from the Foreign Activities Branch of the USBR, we compare the participation rates from 16 countries in South Asia and the Middle East. India, Turkey, and Egypt had the highest rates of participation, followed by Pakistan, Iran, and Israel. The frequency of visits is influenced by political, economic, cultural, and institutional factors. But the most important factors appear to be foreign relations and geopolitics. Given the problems faced by national irrigation bureaucracies around the world, there is a need to focus more directly on political factors than in the past.     

Sustainability of conjunctive water use for salinity control in irrigation areas: theory and application to the Shepparton region,Australia

The long term sustainability of conjunctive water use for controlling irrigation salinity is affected by increase in groundwater salinity over time. This paper uses mass conservation of salt and water to assess groundwater degradation over long time scales. Management options which affect this rate of degradation are also examined. The groundwater model developed is illustrated using data from the Shepparton Irrigation Region in the Murray Basin, Australia. The model predicts rapid groundwater deterioration when conjunctive use is conducted over only a fraction of the area of influence of a groundwater pump. Where the pumped aquifer is underlain by deeper groundwaters, the rate of groundwater degradation is also affected by leakage into or out of the conjunctive use system. Surface redistribution of groundwater from pumps installed in zones of regional groundwater discharge to areas recharging the regional groundwaters, reduces excessive degradation in the zones of discharge. With optimal surface distribution of groundwater, the rate of degradation is low. The rate of groundwater degradation also depends on salt inputs from irrigation water and rainfall, and the average depth from the soil surface to the base of the aquifer. The rate of degradation resulting from applied salts in surface water and rainfall is typically about 0.01 dSm^-1 per year for shallow aquifers in the Shepparton region, but the rate is lower where deeper aquifers are pumped. Partial irrigation also reduces the rate of degradation because of the reduced rate of salt inputs. Where poorer quality groundwater lies within the area of influence of the groundwater pump, a greater rate of deterioration in the quality of pumped groundwater can be expected from groundwater mixing. In some irrigation regions limited export of groundwater through surface water conveyance structures to a river is possible, so that a regional surface salt balance could be maintained. However, salt exports made equal to the rate of surface imports into the irrigated area will only significantly impact groundwater salinity in the very long term, or where only shallow aquifers can be pumped. In addition, this export can be costly for downstream water users, or if construction of additional conveyance infrastructure is extensive; export can have a detrimental impact on riverine ecosystems. Other management options such as the depth of pump installation and the spatial distribution of irrigation water and pumped groundwater, which affect the redistribution of salts within the groundwater system, have the potential to have a much greater impact on local groundwater salinity.