They have been successfully used in orchards, vineyards, and vegetable crops in many regions around the world with salinity problems, including Australia, Israel, California, Spain, and China.They are well suited because of their use of high frequency irrigation, thereby preventing dry soil conditions so that soil solution salinities remain close to that of the irrigation water, especially in the vicinity of the emitters where root density is highest.The salt distribution that develops around a micro-irrigation system depends on system type, but typically salts concentrate on the periphery of the wetted bulb for a surface drip irrigation, whereas salt concentrations typically increase with soil depth for sprinkler systems.The upwards capillary movement of water from the wetted soil depth near the subsurface drip emitter results in soil surface salt accumulation as water is lost through root water uptake and soil evaporation.For conditions where seasonal rainfall is inadequate to push those salts near the soil surface further down, options include preseason flood irrigation or sprinkling, moving drip lines every so many years when replacing or change crop rows between seasons.However, anecdotal evidence in the San Joaquin valley orchards has shown that salinity around drip irrigation systems can limit the volume of the root zone thereby limiting nutrient uptake, particularly nitrogen.The residual nitrogen ends up being leached to groundwater either by excess irrigation or winter recharge causing environmental degradation of groundwater quality.The complex interactions between soil salinity stress and water and nitrate applications were discussed in a model simulation study by Vaughan and Letey.
Libutti and Monteleone suggested that since soil salinity management is bound to increase the leaching of N,hydroponic net pots best practices should optimize the volume of water needed to reduce salinity and that required to avoid or minimize NO3 contamination of groundwater.They suggested to “decouple” irrigation and fertigation.Abating this salinity-N paradox with coupled nutrient-salt management will requires site specific considerations.Because of the potentially high control of irrigation amount and timing, it has been shown by Hanson et al., that subsurface drip directly below the plant row can effectively be used for irrigation under shallow water table conditions as long as the groundwater salinity is low.They showed that converting from furrow or sprinkler to subsurface drip is economically attractive and can achieve adequate salinity control through localized leaching for moderately salt-sensitive crops such as processing tomatoes, eliminating the need for drainage water disposal if so relevant.Controlled drainage —Whereas conventionally drains are installed in conjunction with irrigation systems in arid regions, controlled drainage systems originate in humid regions by control of the field water table using more shallow depth drainage laterals and control structures in the drainage ditches or sumps.In controlled drainage systems, irrigation and drainage are part of an integrated water management system where the drainage system controls the flow and water table depth in response to irrigation.Depending on objectives of the CD system, it can reduce deep percolation and nitrate concentrations in drainage water, augment crop water needs by shallow groundwater contribution, and reduce drainage water volume and salt loads for disposal.
Use of marginal waters—When freshwater resources are limited, salt tolerant crops can be irrigated with more saline water to be reused, for example by treated wastewater or drainage water.Management options include to apply irrigation water that is a mixture of saline with fresh water or cycle saline water with fresh water depending on growth stage , by using crop rotations between salt sensitive and salt tolerant crops, depending on when more saline water is available or through the use of sequential cropping as described in Ayars and Soppe.In addition to reducing freshwater requirements, it decreases the volume of drainage water required for disposal or treatment.A series of articles that present use of marginal waters has been edited by Ragab.In general, research results in this issue demonstrate that waters of much poorer quality than those usually classified as “suitable for irrigation” can, in fact, be used effectively for the growing of selected crops under a proper integrated management system, as long as there are opportunities for leaching to prevent detrimental effects, such as by sodicity.Studies have shown that drip irrigation gives the greatest advantages, whereas sprinkling may cause leaf burn.Cycling strategies are generally preferred, but beneficial effects decreased under DI.In addition, blending does not require added infrastructure for mixing the different water supplies in the desired proportions.Precision agriculture is increasingly becoming an established farming practice that optimizes crop inputs by striving for maximum efficiencies of those inputs thus increasing profitability while at the same time reducing the environmental footprint of those improved practices.While farming has always been about maximizing yield and optimizing profitability, precision farming has allowed for differential application of crop inputs across the farmer’s field, leading to more sustainable management.PA became possible through the broad availability of global positioning system and geographical information system technologies with satellite imagery in the 1980s.
It was focused on achieving maximum yields, despite spatial variations in soil characteristics across agricultural fields.It enabled farmers to vary fertilizer rates across the field, guided by grid or zone sampling.Therefore, inherent to precision agriculture is the use and refinement of the field soil map, in combination with soil and/or plant sensors.Whereas early PA applications depended solely on the soil map and its refinement, more sophisticated approaches have been introduced because of the parallel development of on-the-go sensor technologies, allowing for real-time soil and/or plant monitoring during the growing season thus expanding PA toward spatio-temporal applications.For a review of a broad range of such on-the-go-sensors, we refer to Adamchuk et al., including electrical/electromagnetic and electrochemical sensors for soil salinity and sodium concentration measurements.Whereas specific electrode sensors are available to measure Na concentration in soil solution, most of the EM sensors were developed to indirectly measure soil moisture by correcting for salinity interference, or to measure bulk soil ECb.The sole exception is the porous matrix sensor that was originally designed by Richards and reviewed by Corwin, measuring directly the electrical conductivity of in-situ soil pore water through an electrical circuit with the electrodes embedded in a small porous ceramic element that is inserted in the soil.The EC measurement is solely a function of the solution salinity because the air entry value of the ceramic is such that it will not desaturate beyond 1 bar.Corrections are required for temperature and response time for ions to diffuse from the soil solution into the ceramic.In their synthesis of high priority research issues in PA, McBratney et al.addressed the need to consider temporal variations, as yields typically vary from year to year.For irrigation applications, knowledge of within season variations are critical for BMP’s that minimize crop water and salinity stress.This has led to the term and application of Precision Irrigation, adhering to the definition of PA but applied to irrigation practices.Whereas traditional irrigation management strives for uniform irrigation across the irrigated field, it is the goal of PI to apply water differentially across the field to account for spatial variation of soil properties and crop needs, thus to also minimize adverse environmental impacts and maximize efficiencies.Moreover, PI advances allows for temporal adjustments of irrigation during the growing season because of changing weather conditions,blueberry grow pot including accounting for rainfall.PI can adjust water/ fertilizer amounts because of differential tree/crop needs , by controlling both application rate and timing at the individual tree/crop level or for larger management units.PI uses a whole-systems approach, with the goal to apply irrigation water and fertilizers using the optimal combination of crop, water, and nutrient management practices.As defined by Smith and Baillie , precision irrigation meets multiple objectives of input use efficiency, reducing environmental impacts, and increasing farm profits and product quality.
It is an irrigation management approach that includes four essential steps of data acquisition, interpretation, automation/control and evaluation.Typically, data acquisition is achieved by sensor technologies, while data interpretation would occur by evaluating simulation model outcomes, e.g.of crop response and salt leaching.Control is achieved by automatic controllers of the irrigation application system using information from both the sensors and simulation models, whereas evaluation closes the loop through adjusting the PI system.In addition to electrochemical sensors such as specific electrodes, optical reflectance devices such as near- and mid-infrared spectroscopy methods have been developed to quantify specific soil ion concentrations, particularly soil nitrate content.Over the past 20 years or so, many new soil moisture and salinity sensors have come to market, most of them being able to be included in wireless data acquisition networks.Selected reviews and sensor comparisons include Robinson et al.and Sevostianova et al..Shahid et al.showed the field results of a real-time automated soil salinity monitoring and data logging system, tested at the ICBA Dubai Center for Biosaline Agriculture.Recently there has been increased use of geophysical techniques for delineation of PI irrigation zones and for in-season irrigation and soil salinity management.For example, Foley et al.demonstrated the potential of using ERT and EM38 geophysical methods for measuring soil water and soil salinity in clay soils although they emphasized the need for calibration.Whereas traditionally, one would consider only drip or micro-sprinkler irrigation as a PI method, the broader definition can apply to most pressurized irrigation methods.Specifically, Variable Rate Irrigation is applied to center pivot, lateral move, and solid set systems, as reviewed recently by O’Shaughnessy et al..Many of the aspects of PI equally apply to such sprinkler systems, however, it is noted that their inherent complexity has precluded the required development of user-friendly interfaces for decision support, lagging the engineering technology.Specifically, the need to fuse GIS, remote sensing, and other temporal information with the DSS, allowing management zones to change over the growing season.Recent evaluations on impacts of using VRI on crop yield, water productivity were presented by Barker et al.and Kisekka et al., showing potential improvements when using VRI or MDI , but that additional research is strongly advocated especially because of the significant increased investments required.Another limitation to date of adoption of PI is that large-scale VRI systems require many sensors which can be cost-prohibitive, whereas determining their placement and number of sensors needed is not straightforward.It is worth noting that PI can also be applied to surface irrigation systems as described in Smith and Baillie.For example, automated gates coupled with SCADA systems and real-time data analytics can be used to optimize flow rates, and advances times to ensure infiltration rates match variable soil conditions.The application of PI to maintain plant-tolerable soil salinity levels was introduced by Raine et al., identifying research priorities at the time that allows for PI to be effective and pointing out that the level of precision, water application uniformity and efficiencies of most irrigation practices is sub-optimal.Among identified knowledge gaps was the lack of agreement between field and model-simulated data, especially for multidimensional model applications such as required for drip irrigation and for spatially-variable salt and water distributions at the individual plant root zone scale.This puts into question the usefulness of computer modeling for soil salinity management purposes, especially if there is general absence of soil salinity measurements to validate model simulations.Another limitation of successful PI is the lack of information on crop root response to salinity when considering the whole rooting zone in multiple dimensions as well as on crop growth stage.A central component of a road map toward precision irrigation is moving from a single management point within an agricultural field toward defining management zones across the field and eventually close to a plant-by-plant level of resolution were appropriate.It requires cost-effective sensors, wireless sensing and control networks, automatic valve control hardware and software, real-time data analytics and simulation modeling, and a user friendly and visual decision support system.Many sensor types and technologies are being developed and are introduced for soil moisture sensing; however, few applications include soil salinity sensing in concert with soil moisture monitoring.For PI to advance further, there is great need for much improved and cost-effective multi-sensor platforms that combine measurements of soil salinity with soil moisture and nitrate concentration.For a recent review of contemporary wireless networks and data transfer methods, we refer to Ekanayake and Hedley , that includes the use of cloud-based databases with smart phone apps and web pages.