Irrigation management from space: Towards user-friendly products

Irrigation Advisory Services (IAS) are the natural management instruments to achieve a better efficiency in the use of water for irrigation. IAS provide the farmers with irrigation scheduling information, based on crop water requirements for different crops, and thus, help farmers to optimise production and cost-effectiveness. Current IAS rely on labour- and cost-intensive field work, yet are unable to cover each plot in large areas at regular short time intervals. Earth observation (EO) is naturally destined to fill this gap. It allows for efficiently monitoring crop water requirements and related parameters within each field in extended areas. The incorporation of IT in the generation and distribution of information makes that information easily available to IAS and to its associated farmers in a personalised way. Farmers can opt to receive a wide variety of products, tailored to their needs and infrastructure, ranging from simple irrigation scheduling recommendation (irrigation volume, time) to colour-coded images (providing quick intuitive information on the crop vigour within their plots), both on PC and/or mobile phones. This work is based on the project DEMETER (DEMonstration of Earth observation TEchnologies in Routine irrigation advisory services), which assesses and demonstrates the EO- and IT-induced improvements in IAS day-to-day operations. This paper describes the methodology and discusses examples of products.     

海子水库灌区节水型灌溉制度的制定

本文介绍了中日双方专家团在海子水库灌区现场调查中,实测土壤水分特征值的方法,土壤水分曲线的制定和应用,负压计观测值的应用,计算节水型灌溉用水量和灌水间隔日数的方法,并用节水型频繁灌溉法制定了各作物的节水型灌溉制度,用这种方法制定的节水型灌溉制度要比我国过去用的常规法节水40%以上。     

Deficit irrigation in maize for reducing agricultural water use in a Mediterranean environment

Research on crop response to deficit irrigation is important to reduce agricultural water use in areas where water is a limited resource. Two field experiments were conducted on a loam soil in northeast Spain to characterize the response of maize (Zea mays L.) to deficit irrigation under surface irrigation. The growing season was divided into three phases: vegetative, flowering and grain filling. The irrigation treatments consisted of all possible combinations of full irrigation or limited irrigation in the three phases. Limited irrigation was applied by increasing the interval between irrigations. Soil water status, crop growth, above-ground biomass, yield and its components were measured. Results showed that flowering was the most sensitive stage to water deficit, with reductions in biomass, yield and harvest index. Average grain yield of treatments with deficit irrigation around flowering (691 g m⁻²) was significantly lower than that of the well-irrigated treatments (1069 g m⁽²). Yield reduction was mainly due to a lower number of grains per square metre. Deficit irrigation or higher interval between irrigations during the grain filling phase did not significantly affect crop growth and yield. It was possible to maintain relatively high yields in maize if small water deficits caused by increasing the interval between irrigations were limited to periods other than the flowering stage. Irrigation water use efficiency (IWUE) was higher in treatments fully irrigated around flowering.     

Impact of irrigation timing on simulated water-crop production functions

Estimates of the effects of alternative discrete irrigation water scheduling options on consumptive use or evapotranspiration and on crop yield are developed for a northeastern Colorado case study. The analysis proceeds from the premise that farmers, rather than considering irrigation water as a continuously variable input, tend to treat irrigations as discrete events, and make scheduling decisions as choices among numbers of irrigations of approximately equal volume. The van Genuchten-Hanks model is employed to develop a transient-state water-crop production function model. Results for two crops – corn grain and edible dry beans – are presented here. Findings are that the effect of the number of irrigations on evapotranspiration and yield per hectare varies widely, depending upon the timing of applications. When farmers can choose the optimal timing of irrigations, a reduced number of irrigations has a relatively limited adverse effect on crop production until irrigations are reduced to less than four per season. However, there are many situations in which an inability to apply water can result in a very large reduction from potential maximum yield, particularly if water is withheld early in the season and/or during the rapid growth period of the crops. In many contexts of irrigation water management, water policy analysts will wish to consider the more realistic discrete-input simulation model for policy evaluation. Received: 1 November 1996     

Real-time adaptive irrigation scheduling under a limited water supply

The problem of real-time irrigation scheduling under limited water supply is considered. The goal is to develop an irrigation operation policy which maximizes crop yields and is responsive to current season changes in weather and other variables. Because irrigation decisions are sequential and dependent on crop and soil water status, and also because crop yields can only be known at the end of the season, the decisions are arrived at by a two-stage process. In the first or the design stage, irrigations are planned for the entire season at weekly intervals using historical data and an optimal irrigation scheduling model. In the second stage, the decisions for the subsequent weeks are revised each week after updating the status of the system with real time data up to that week and solving the irrigation optimization model once again for the new conditions. Thus, each week an irrigation decision is made, the entire planning horizon is kept in view. The procedure is illustrated by application to a case study.     

Evaluation of options for increasing yield and water productivity of wheat in Punjab, India using the DSSAT-CSM-CERES-Wheat model

The DSSAT-CSM-CERES-Wheat V4.0 model was calibrated for yield and irrigation scheduling of wheat with 2004–2005 data and validated with 13 independent data sets from experiments conducted during 2002–2006 at the Punjab Agricultural University (PAU) farm, Ludhiana, and in a farmer's field near PAU at Phillaur, Punjab, India. Subsequently, the validated model was used to estimate long-term mean and variability of potential yield (Y_p), drainage, runoff, evapo-transpiration (ET), crop water productivity (CWP), and irrigation water productivity (IWP) of wheat cv. PBW343 using 36 years (1970–1971 to 2005–2006) of historical weather data from Ludhiana. Seven sowing dates in fortnightly intervals, ranging from early October to early January, and three irrigation scheduling methods [soil water deficit (SWD)-based, growth stage-based, and ET-based] were evaluated. For the SWD-based scheduling, irrigation management depth was set to 75 cm with irrigation scheduled when SWD reached 50% to replace 100% of the deficit. For growth stage-based scheduling, irrigation was applied either only once at one of the key growth stages [crown root initiation (CRI), booting, flowering, and grain filling], twice (two stages in various combinations), thrice (three stages in various combinations), or four times (all four stages). For ET-driven irrigation, irrigations were scheduled based on cumulative net ETo (ETo-rain) since the previous irrigation, for a range of net ETo (25, 75, 125, 150, and 175 mm). Five main irrigation schedules (SWD-based, ET-driven with irrigation applied after accumulation of either 75 or 125 mm of ETo, i.e., ET75 or ET125, and growth stage-based with irrigation applied at CRI plus booting, or at CRI plus booting plus flowering stage) were chosen for detailed analysis of yield, water balance, and CWP and IWP. Nitrogen was non-limiting in all the simulations.Mean Y_p across 36 years ranged from 5.2 t ha⁻¹ (10 October sowing) to 6.4 t ha⁻¹ (10 November sowing), with yield variations due to seasonal weather greater than variations across sowing dates. Yields under different irrigation scheduling, CWP and IWP were highest for 10 November sowing. Yields and CWP were higher for SWD and ET75-based irrigations on both soils, but IWP was higher for ET75-based irrigation on sandy loam and for ET150-based irrigation on loam. Simulation results suggest that yields, CWP, and IWP of PBW343 would be highest for sowing between late October and mid-November in the Indian Punjab. It is recommended that sowing be done within this planting period and that irrigation be applied based on the atmospheric demand and soil water status and not on the growth stage. Despite the potential limitations recognised with simulation results, we can conclude that DSSAT-CSM-CERES-Wheat V4.0 is a useful decision support system to help farmers to optimally schedule and manage irrigation in wheat grown in coarse-textured soils under declining groundwater table situations of the Indian Punjab. Further, the validated model and the simulation results can also be extrapolated to other areas with similar climatic and soil environments in Asia where crop, soil, weather, and management data are available.     

Supplemental irrigation of wheat with saline water

In arid and semi-arid regions, both rainfall and surface irrigation water supplies are unreliable and inadequate to meet crop water requirement. Groundwater in these regions is mainly marginally saline (2-6 dS/m) to saline (>6 dS/m) and could be exploited to meet crop water requirement if no adverse effects on crops and land resource occur. The fear of adverse effects has often restricted the exploitation of naturally occurring saline water. The results reveal that substituting a part or all except pre-sowing irrigation with saline water having an electrical conductivity (EC_iw) of 8 dS/m is possible for cultivation of wheat. Similarly, saline water with EC_iw ranging between 8 and 12 dS/m could be used to supplement at least two irrigations to obtain 90% or more of the optimum yield. In low rainfall years, the use of such waters for all irrigations, except pre-sowing, produced more yield than skipping irrigations. Apparently, even at this level of osmotic salt stress, matric stress is more harmful. Thus, it would be interesting to use such waters for wheat production in monsoon climatic regions.     

Management guidelines for efficient irrigation of vegetables using closed-end level furrows

Closed-end level furrows are commonly used to irrigate vegetables in the Lower Colorado River region (LCRR). The application efficiency of furrow irrigation in this area is often low. The objective of this study is to develop management tools and guidelines for the efficient irrigation of vegetables using closed-end level furrows. The study consisted of field experiment and modeling (model calibration, model verification, and the development of management tools by simulation). Field experiments were performed over a period of 27 months. Infiltration parameters were estimated for four soil textural groups (i.e., moderately coarse textured, medium textured, moderately fine textured, and fine textured soils) using a two-point method modified for closed-end level furrows. Model verification shows that the surface irrigation hydraulic model used in this study (SRFR) is capable of simulating the furrow irrigation process with acceptable levels of accuracy. Results of the study also indicate that adequate and efficient irrigations can be achieved using closed-end level furrows through the proper selection of unit inlet flow rate, Q_o, and cutoff time, t_co. However, given the soil and crop combinations in the LCRR, sometimes significant increases in irrigation efficiency, compared to present levels, can be attained only if furrow lengths are shorter than the typical size currently in use in the LCRR. Limitations of the proposed management tools and on-going research to address these limitations are briefly discussed.     

河西绿洲灌区主要作物需水量及作物系数试验研究

利用Penman-Monteith公式计算了甘肃张掖绿洲主要作物各生育期参考作物蒸散量,利用农田水量平衡方程及土壤水分胁迫系数计算了作物实际蒸发蒸腾量,并计算比较了充分灌溉和非充分灌溉条件下不同生育期作物需水特征,确定了非充分灌溉条件下主要作物的作物系数。结果表明,非充分灌溉条件下,主要作物各生育期需水规律和充分灌溉具有一致变化趋势。非充分灌溉条件下,小麦、玉米、马铃薯全生育期作物系数平均值分别为0.81、0.7和0.73。在全生育期当中,随生育期的延续,主要作物叶面蒸腾比例逐渐增大,棵间蒸发逐渐减少。     

The soil water balance of rainfed and irrigated oats,Italian rye grass and rye using the CropSyst model

Crop growth models have been used in simulating the soil water balance for purposes of irrigation management and yield predictions. The application of CropSyst, a cropping systems simulation model, was evaluated for Cedara, South Africa. Simulations included soil water balance of fallow land and rainfed and irrigated winter crops [oats (Avena sativa), Italian ryegrass (Lolium multiflorum) and rye (Secale cereale)]; and irrigation scheduling of the winter crops. Soil, plant, weather and management inputs were used for the soil water balance simulations. Model crop parameters were used from past experiments or obtained from model documentation, with a slight modification to account for varietal differences. The fallow land soil water simulations were more accurate for dry than for wet soil. For all three winter crops, the model consistently over-estimated the soil water content in the upper layers, with a good agreement for the deeper layers until a large precipitation event occurred to which the model responded more slowly than that observed. Simulations using model-scheduled irrigation based on 0.4 and 0.6 maximum allowable depletion criteria indicated that the observed applied irrigation in the field was more than that required. Soil water depletion and accumulated transpiration simulations were similar in both the observed and model-scheduled irrigations, but total soil evaporation and percolation were greater in the case of the observed than the model-scheduled irrigations. Irrigation scheduling using crop growth models may assist in avoiding over- or under-application of irrigation applications by ensuring efficient utilization of rain and irrigation.     

灌区灌溉用水时空优化配置方法

将传统的灌溉水量在作物间的优化分配模型和建立的渠系工作制度多目标优化模型与地理信息系统相集成,提出了基于空间决策支持系统的灌区灌溉用水优化配置的新方法.综合考虑了灌区内作物、土壤、气象站点、渠系布置的空间差异、年季间气象以及作物不同生育阶段对应参数的时间差异.与传统优化方法相比,该方法可根据管理者对优化精度的要求,灵活选择优化尺度,同时,简化了求解时空优化配水问题的繁琐程度,结果表现形式更加丰富.在此基础上建立的空间决策支持系统界面友好,运行效率高,可移植性和通用性强.经实例验证,优化后的配水方案与原配水方案相比较,灌溉总用水量减少296％,产量增加243％,水分生产率提高05 kg／m3,灌溉净效益增加168％.优化后配水方案具有将有限的水资源向经济价值较高作物转移的趋势.该方法为灌区灌溉用水优化配置提供了新思路.     

A simple irrigation scheduling approach for pecans

Pecans are a major crop in New Mexico's Lower Rio Grande Valley (LRGV). It is estimated that New Mexico is responsible for about 21% of the world's pecan production (Lillywhite et al., 2007). Currently, approximately 12,000 ha of pecan orchards at various stages of growth consume 45% of the area's irrigation water. Pecan evapotranspiration (ET) varies with age, canopy cover, soil type, crop density and method of water management. Intense competition for the LRGV's limited water supply has created a serious need for better water management through improved irrigation scheduling. Annual pecan ET ranges from as low as 500 mm to as high as 1400 mm. Diversity of the pecan crop coefficient (K_c) and ET makes the task of irrigation scheduling for this crop very complicated. Using remote sensing technology and field ET measurements, a simple relationship was developed to relate crop coefficient and ET to canopy cover. This relationship is then used in combination with climate data to calculate daily and weekly water requirements for each orchard. The difference between annual ET values estimated from canopy cover and values measured with an eddy covariance flux tower ranged from 2 to 5%. The average ratio of estimated monthly ET values over measured ET values was 1.03 with the standard error of the estimate ranging from 10 to 20 mm/month. This methodology provides a simple tool that farmers can use to schedule irrigation of pecan orchards. Even though the methodology was developed for irrigation scheduling in the LRGV, it can be used in other locations by transferring the reference crop coefficients using K_c-GDD relationships.     

引黄灌区灌溉效益优化计算模型

以引黄灌区为研究对象 ,在分析传统灌溉效益计算方法不足的基础上 ,按水资源合理配置的要求 ,基于作物的节水灌溉制度 ,提出引黄灌区灌溉效益优化计算的双层线性规划模型 ,开发了相应的计算软件。模型考虑了引黄水量在不同作物间和同种作物不同灌溉时段间的优化配置 ,使灌溉效益计算更趋合理     

On-farm performance evaluation of improved traditional small-scale irrigation practices: A case study from Dire Dawa area, Ethiopia

Field evaluation of surface irrigation systems play a fundamental role to determine the efficiency of the system as it is being used and to identify management practices and system configurations that can be implemented to improve the irrigation efficiency. This study evaluated the performance of an ‘improved’ traditional small-scale irrigation practice at Adada, a representative small-scale irrigation practice in Dire Dawa Administrative Council, Eastern Ethiopia. In order to determine numerical values of performance measures, certain parameters were measured/observed before, during and after an irrigation event while farmers are performing their normal irrigation practice. These parameters include: irrigated crop, irrigation method, stream size, cutoff time, soil moisture deficiency, and field size, shape and spacing. The results showed that the irrigation water applied to a farmer's plot during an irrigation event/turn was generally higher than the required depth to be applied per event. Since the irrigation method used was end-dyked, the major cause of water loss was due to deep percolation. The deep percolation loss was 32% in sorghum, 57% in maize, and 70% in tomato and potato fields. The type of irrigation system used, the ridged irrigation practice and the poor irrigation scheduling in the study sites were the main problems identified in the management and operations of the schemes. The following corrective measures are recommended to improve the system: (1) farmers should regulate the depth of irrigation water they apply according to the type of crop and its growth stage, change the field irrigation system and/or configuration especially for shallow rooted row crops, to furrow system, (2) guidance and support to farmers in developing and introduction of appropriate irrigation scheduling, and (3) future development interventions towards improvement of traditional irrigation practices should also focus in improving the on farm irrigation systems in addition to improving physical infrastructure of the scheme.     

Optimal irrigation planning model for an existing storage based irrigation system in India

A weekly irrigation planning LP model is formulated for determining the optimal cropping pattern and reservoir water allocation for an existing storage based irrigation system in India. Objective of the model is maximization of net annual benefit from the project. In an irrigation planning of a storage based irrigation system, initial storage of the reservoir at the beginning of the reservoir operation, expected inflows into the reservoir during each intraseasonal period, capacity of channels, crop calendar and yield response to water deficit in each growth stage of crop play a vital role in deciding acreage and water allocation to each crop. The planning model takes into account yield response to water deficit in each intraseasonal period of the crop, expected weekly inflows entering into the reservoir, storage continuity of reservoir, land and water availability, equity of water allocation among sub areas and proportionate downstream river release. One year comprising of 52 weeks is considered as planning horizon. To account for uncertainty in water resources availability, the model is solved for four levels of reliability of weekly inflows entering into the reservoir (90%, 85%, 80% and 75%). Alternative optimal cropping patterns and weekly releases to crops grown in each sub area under each main canal are obtained for various states of initial storage at the beginning of reservoir operation and for various levels of weekly inflows into the reservoir. Results reveal the importance of initial state of reservoir storage for feasible solution and shows the impact on cropping pattern with the change in initial storage of reservoir for different levels of reliability of weekly inflows.     

实用型滴灌灌溉计划制定方法

介绍了适合日光温室、塑料大棚等设施栽培和小块农田经济作物栽培滴灌灌溉计划制定的2种方法。方法一：将真空表负压计埋在滴头正下方20cm深度处监测土壤水势，每次的灌水量相同，或者将作物整个生育期分为2～3个生长阶段，每个生长阶段内每次的灌水量相同．只要土壤水势超出预定的范围，就进行灌溉。对于大部分作物，只要每次的灌水量在5mm左右，土壤水势保持在25～35kPa的范围内，就能获得比较理想的产量。方法二：在冠层顶部放置一个20cm标准蒸发皿，灌溉频率一定．将一个灌水周期内蒸发皿的蒸发量乘以比例系数作为下一个灌水周期的灌水量。对于大部分日光温室和塑料大棚栽培的作物来说，只要将这个比例系数定为1，灌水周期定为每天1次、每2天1次或每3天1次，就能获得比较理想的产量。     

Conjunctive use of saline and non-saline irrigation waters in semi-arid regions

In arid and semi-arid regions, effluent from sub-surface drainage systems is often saline and during the dry season its disposal poses an environmental problem. A field experiment was conducted from 1989 to 1992 using saline drainage water (EC=10.5–15.0 dS/m) together with fresh canal water (EC=0.4 dS/m) for irrigation during the dry winter season. The aim was to find if crop production would still be feasible and soil salinity would not be increased unacceptably by this practice. The experimental crops were a winter crop, wheat, and pearl-millet and sorghum, the rainy season crops, grown on a sandy loam soil. All crops were given a pre-plant irrigation with fresh canal water. Subsequently, the wheat crop was irrigated four times with different sequences of saline drainage water and canal water. The rainy season crops received no further irrigation as they were rainfed. Taking the wheat yield obtained with fresh canal water as the potential value (100%), the mean relative yield of wheat irrigated with only saline drainage water was 74%. Substitution of canal water at first post-plant irrigation and applying thereafter only saline drainage water, increased the yield to 84%. Cyclic irrigations with canal and drainage water in different treatments resulted in yields of 88% to 94% of the potential. Pearl-millet and sorghum yields decreased significantly where 3 or 4 post-plant irrigations were applied with saline drainage water to previous wheat crop, but cyclic irrigations did not cause yield reduction. The high salinity and sodicity of the drainage water increased the soil salinity and sodicity in the soil profile during the winter season, but these hazards were eliminated by the sub-surface drainage system during the ensuing monsoon periods. The results obtained provide a promising option for the use of poor quality drainage water in conjunction with fresh canal water without undue yield reduction and soil degradation. This will save the scarce canal water, reduce the drainage water disposal needs and associated environmental problems.     

Irrigation modernization and water conservation in Spain: The case of Riegos del Alto Aragón

This study analyzes the effects of irrigation modernization on water conservation, using the Riegos del Alto Aragón (RAA) irrigation project (NE Spain, 123354 ha) as a case study. A conceptual approach, based on water accounting and water productivity, has been used. Traditional surface irrigation systems and modern sprinkler systems currently occupy 73% and 27% of the irrigated area, respectively. Virtually all the irrigated area is devoted to field crops. Nowadays, farmers are investing on irrigation modernization by switching from surface to sprinkler irrigation because of the lack of labour and the reduction of net incomes as a consequence of reduction in European subsidies, among other factors. At the RAA project, modern sprinkler systems present higher crop yields and more intense cropping patterns than traditional surface irrigation systems. Crop evapotranspiration and non-beneficial evapotranspiration (mainly wind drift and evaporation loses, WDEL) per unit area are higher in sprinkler irrigated than in surface irrigated areas. Our results indicate that irrigation modernization will increase water depletion and water use. Farmers will achieve higher productivity and better working conditions. Likewise, the expected decreases in RAA irrigation return flows will lead to improvements in the quality of the receiving water bodies. However, water productivity computed over water depletion will not vary with irrigation modernization due to the typical linear relationship between yield and evapotranspiration and to the effect of WDEL on the regional water balance. Future variations in crop and energy prices might change the conclusions on economic productivity.     

气候变化对区域农业灌溉用水影响分析

从气候变化对区域灌溉用水影响机理入手,利用区域经济发展、灌溉用水、种植结构等因素之间动态反馈关系,采用系统动力学建模方法,构建了气候变化背景下灌溉用水响应模型,分析了未来不同气候情景下宝鸡峡灌区灌溉用水的变化过程。结果表明,随着未来气温升高趋势的增加,灌溉用水亦呈明显升高趋势,不同情景稍有差异,但差别不大,而不同作物间差异较大。以B1情景为例,温度升高1℃,灌区内灌溉净需水量约增加12050×104m3,毛需水量约增加20080×104m3,灌区内小麦单位面积约增加需水量28m3/亩;玉米约增加8m3/亩,这可能与冬小麦和夏玉米生育期的变化有关,应进一步加强研究。     

套种条件下限水灌溉对小麦生长影响的初步试验研究

为了研究套种条件下作物耗水规律和非充分灌溉制度,对河套灌区的主要农作物小麦进行不同灌水量和不同种植模式下生理指标的对比,研究了不同灌水量及不同种植条件对作物产量及作物生长状况的影响。研究分析表明,在相同灌水处理条件下,套种小麦的穗粒数、产量均高于单体种植;拔节期的水分亏缺对小麦的产量影响最大,而灌浆期的灌水量影响最小;在套种模式下更有助于小麦对氮素的吸收。