Assessment of AquaCrop Model in Simulating Sugar Beet Canopy Cover,Biomass and Root Yield under Different Irrigation and Field Management Practices in Semi-Arid Regions of Pakistan

The AquaCrop model was analyzed for simulating sugar beet crop production under four irrigation regimes, three mulching conditions and three furrow irrigation systems in semi-arid region of Pakistan. Irrigation regimes were full irrigation (FI), 20% deficit irrigation (DI₂₀), 40% deficit irrigation (DI₄₀) and 60% deficit irrigation (DI₆₀). The mulching practices were No-mulch (NM), black film mulch (BFM) and straw mulch (SM). The furrow irrigation systems were conventional ridge-furrow (CRF) system, medium raised-bed (MRB) system and wide raised-bed (WRB) system. The model was calibrated and validated using the independent data sets of full irrigation and deficit irrigation regimes collected during 2011–12 cropping season. The model performance was evaluated by using different statistical indicators such as Root Mean Square Error (RMSE), index of agreement (d_index), and Nash–Sutcliffe Efficiency (NSE). These indicators showed that the model fairly simulated sugar beet canopy cover for all treatments with 3.00 ≤ RMSE ≤ 16.89, 0.84 ≤ d_index ≤ 0.97, and 0.76 ≤ NSE ≤ 0.99. For biomass and root yield, the model performance was excellent under all full irrigation (FI) and mild deficit irrigation (DI₂₀) treatments with RMSE ranged between 0.07 and 1.17, d_index between 0.48 and 0.84, and NSE between 0.42 and 0.86, respectively. However the low values of d_index (0.10 and 0.13) and NSE (?69.32 and ?30.63) showed that the model overestimated both the biomass and root yield when 20% deficit irrigation was applied without mulch in WRB system. The model also over estimated the yield and biomass when 40% deficit irrigation was applied in CRF system. The highest overestimation (d_index: 0.10 to 0.11; NSE: ?50.92 to ?70.55) was observed when highest stress level (DI₆₀) was applied in the presence of BFM in CRF system. Based on the model’s overall performance, the AquaCrop application is recommended for developing efficient farm water management strategies in the semi-arid regions.     

Crop Water Productivity of Irrigated Teff in a Water Stressed Region

In water stressed regions such as the Central Rift Valley of Ethiopia, increasing Crop Water Productivity (CWP) is imperative for sustainable food and water security. This paper presents CWP of Teff (Eragrostic Tef), a staple food in Ethiopia and an important export crop. Field experiments were conducted under irrigated agriculture during the dry seasons in the periods: 1) November 2010 to March 2011; and 2) December 2011 to April, 2012 at Melkassa Agricultural Research Centre in Ethiopia. Teff crop was irrigated at sixteen different water application depths ranging from 100 to 25 % of the optimum Crop Water Evapotranspiration (ETc.) during the four growing stages, the initial, development, mid season and late season. The effect of seeding rates of 25 kg/ha and 10 kg/ha on lodging and yield of the crop was also determined. The main results were: 1) At 25 % deficit irrigation applied for the whole growth period, Teff CWP was the highest at 1.16 and 1.08 kg/m³ respectively for the seeding rates of 25 kg/ha and 10 kg/ha; 2) the CWP slightly decreased to 1.12 and 1.07 kg/m³ when the 25 % deficit was applied during the late season stage; 3) the crop yield response factor (K_y) of 1.09 and 1.19 was obtained for seeding rates of 25 kg/ha and 10 kg/ha respectively; the equivalent biomass response factor (K_y) was less at 0.88 and 0.96 respectively.     

作物水分生产函数及灌溉制度优化的研究进展

阐述了作物水分生产函数的基本原理和一些典型模型,并对其在灌溉方面及不同阶段缺水对作物生物量累积的后效性影响等方面的研究,以及可行性分析及地区移用性研究加以探讨。对作物灌溉制度优化模型以及作物优化灌溉制度设计方法研究加以探讨,分析了目前模型中指数取值研究不足等问题。为合理利用有限水资源,达到最大的作物产量或产值,实现有限水量在作物生长期及作物间的合理配置提供依据。     

The Pros and Cons of Encouraging Shallow Groundwater Use through Controlled Drainage in a Salt-Impacted Irrigation Area

Encouraging shallow groundwater use through water table management or controlled drainage in irrigated areas can relief crop water stress under water shortage condition. But substituting fresh irrigation water with saline groundwater may speed up salinity buildup in the crop root zone, and consequently increase water use for salt leaching. With a proposed analytical model, this paper presents a case study demonstrating the effect of encouraging shallow groundwater use through controlled drainage on salt and water management in a semi-arid irrigation area in northwestern China. Based on the average rainfall condition, the model assumes that salt accumulates in the crop root zone due to irrigation and shallow groundwater use; till the average soil salinity reaches the crop tolerance level, leaching irrigation is performed and the drainage outlet is lowered to discharge the salt-laden leaching water. For the relatively salt tolerant crop–cotton in the study area, the predicted leaching cycle was as long as 751 days using the fresh water (with salinity of 0.5 g/L) irrigation only; it was shortened to 268 days when the water table depth was controlled at 2 m and 23% of the crop water requirement was contributed from the saline groundwater (with salinity of 4.43 g/L). The predicted leaching cycle was 140 days when the water table depth was controlled at 1.5 m and groundwater contribution was 41% of the crop water requirement; it was shortened to 119 days when the water table depth was controlled at 1.2 m and the groundwater contribution was 67% of the crop water requirements. So the benefit from encouraged shallow groundwater use through controlled drainage is obtained at the expense of shortened leaching cycle; but the shallow groundwater use by crops consists of a significant portion of crop water requirements, and the leaching cycle remains long enough to provide a time window for scheduled leaching in the off season of irrigation. Weighing the pros and cons of the encouraged shallow groundwater use may help plan irrigation and drainage practices to achieve higher water use efficiency in saline agricultural areas.     

A New Model for Simulating Supplemental Irrigation and the Hydro-Economic Potential of a Rainwater Harvesting System in Humid Subtropical Climates

Here we have developed a new model to simulate supplemental irrigation and the hydro-economic potential of a rainwater harvesting system in rainfed agricultural areas. Using the model, soil moisture in rainfed crop land, supplemental irrigation requirements, rainwater storage in an on-farm reservoir (OFR) system, and surface and ground water availability were predicted. In an irrigated system, an OFR was used to harvest rainwater during the rainy season, and stored water was applied to cropland as supplemental irrigation (SI). An economic analysis was performed to calculate the benefits due to an OFR irrigation system, and gains from increased crop yield and downstream water availability in the irrigated OFR system were compared with rainfed system (i.e. no OFR). In addition, we calculated the impacts of dry and wet seasons on total value gains (grain and water gains) for irrigated and rainfed conditions and performed a sensitivity analysis to quantify the impacts of model input parameters on total value gains. Analyses showed that the OFR system can produce crop yields three times greater than rainfed agriculture. During a water stress season, the total water use in the irrigated system was 65 % greater than for the rainfed system. Water use efficiency of the irrigated system was 82 % higher than for the rainfed system. In a dry season, the total value gains due to increased crop yield by supplemental irrigation and downstream water availability of the irrigated system were 74 % greater than for the rainfed system, while in a wet season the total value gain of the irrigated system was 14 % greater than for the rainfed system. A precipitation scenario analysis of wet and dry seasons indicated that the benefits of a rainwater harvesting system can be considerably greater in dry seasons than wet seasons.     

Relating Crop Water Consumption to Irrigation Water Supply by Remote Sensing

A new set of irrigation performance indicators based on remote-sensing estimates of evapotranspiration is introduced. These evapotranspiration indicators are the relative evapotranspiration or crop stress and the water efficiency as well as their uniformity. With a remote-sensing evapotranspiration algorithm (SEBAL) maps of actual crop water consumption are derived. These maps are one of the inputs in the evapotranspiration indicators, together with GIS data (digitized irrigation unit boundaries) and field data (irrigation delivery schedule and water flow). This approach is applied on the Rio Tunuyan irrigation scheme, Mendoza, Argentina, which is served by surface water and privately owned ground water pumps. A homogeneous pattern of actual crop water consumption is detected from the highest irrigation level till the lowest (farm) level (coefficient of variance from 8.6% to 6.1% and 14.0% of secondary, tertiary and pixel level, respectively). Considering that a rotational irrigation schedule at tertiary and farm level is present, the results indicate that ground water supply through extraction and capillary rise equalize the spatial patterns in crop water consumption. The latter is proved by a comparison between (i) the areal water consumption from remote-sensing measurements, (ii) the areal water supply and (iii) additional field information on ground water extraction and capillary rise.     

考虑缺水滞后效应的作物-水模型研究

本文依据作物生理学有限缺水理论，考虑作物不同生育阶段缺水对叶面积系数、腾发量变化及产量影响的滞后效应，假设这种滞后影响过程的现在阶段只与将来阶段有关，而将来阶段与过去阶段无关，经单阶段和多阶段缺水的两种田间灌溉试验，求得改进的加法模型即考虑缺水滞后效应的作物水模型（ＬＥＭＣＲＷ），与常见的３种国外ＭＣＲＷ比较具有较广泛的适应性和较好精度，只要正确选用不同的敏感指标，可供单阶段和多阶段缺水对产量影响的非充分灌溉模拟．     

Effect of Various On-Farm Water Management Scenarios on Equity and Productivity in Irrigation Networks

This research investigated the optimum on-farm water management methods for a summer crop (Maize). Water equity and productivity were optimized simultaneously by using genetic algorithms in Doroodzan Irrigation Network. Increase in water reduction fraction (WRF) (0.0 to 0.8) has the incremental effect on water equity (on average 19.4 %), however by increasing WRF, water productivity initially increased (on average 25.3 % at WRF?=?0.4) and then decreased. With increasing irrigation application efficiency (E_a) (40 to 90 %), the values of water equity and productivity increased by on average 52.8 and 91.5 %, respectively. Increment of conveyance efficiency of channels (E_c) (70 to 90 %) resulted in minimum incremental effect on water equity and productivity (on average 18.5 and 11.9 %, respectively). Furthermore, the values of performance measure decreased from wet water year to drought water year. Tape irrigation system was considered as the best choice at low quantities of WRF (<=0.4), however for higher values of WRF (>?=?0.6), sprinkler irrigation system was considered as the best choice for achieving higher values of water equity and productivity. Meanwhile, when equity and productivity were considered together for a specific method of deficit irrigation scheduling, under specified quantity of irrigation water, with increasing equity the water productivity reduction was negligible.     

不同灌水量对绿洲玉米叶面积动态及产量的影响

以河西绿洲春玉米为研究对象,分析了不同灌水量对玉米全生育期叶面积动态、产量及产量构成要素的影响。结果表明:不同灌水处理玉米单株叶面积在灌浆初至灌浆中期达到高峰,且稳定期持续至灌浆末期,此后单株叶面积衰减较快。进入灌浆期以后,不同灌水处理玉米叶面积相对生长率已开始出现负值,叶面积已有开始衰减迹象。与充分灌水相比,有限灌水不仅显著节水31.1%,还可使玉米产量提高2.9%,而有限灌水粒重、行粒数和穗粒数的增加则是玉米节水高产的主要原因。因此,不同灌水量显著影响玉米叶面积生长和产量形成过程,生产中应侧重通过前期有限水分亏缺(拔节期中度水分调亏而大喇叭口-孕穗期轻度调亏)产生的后补偿效应促进生育中后期叶面积的持续稳定发展,从而实现玉米高产和水分高效利用的双赢。     

Probability Analysis of Crop Water Stress Index: An Application of Double Bounded Density Function (DB-CDF)

Soil moisture is an uncertain variable due to rainfall randomness. Furthermore, its density function is hybrid in nature, with spikes at maximum and minimum soil moisture (saturation and field capacity). Both of these properties are also considered for crop water stress index. The crop water stress index can be used to show the sensitivity of a crop to deficit irrigation. In this paper, a new methodology is proposed to probability analysis of water stress index using Double Bounded Density Function (DB-CDF) and moment analysis of crop water stress index. For this purpose, two equations were developed for the first and second moments of water stress index. To find out the value of the proposed moment equations, they are used as constraints in a stochastic model of crop water allocation as developed previously by Ganji and Shekarrizfard (Water Resour Manage 25:547–561, 2010). After verification of the model, the DB-CDF of soil moisture stress index was estimated using the value of proposed moments in the growing periods. The results show that in case of deficit irrigation, the probability of crop water stress occurrence is high and as a consequence, any unpredictable water shortage leads to yield reduction. The application of the proposed methodology is novel and has not been reported in the literature to date.     

充分灌与调亏灌溉条件下桃树滴灌的耗水量研究

本文研究了充分灌与调亏灌溉条件下桃树滴灌的耗水量。在田间设置有两个处理，其一是在整个生育期以蒸发量的80%进行充分灌溉；其二是在果实生长缓慢期以蒸发量的20%进行亏缺灌溉，而在其它季节以蒸发量的80%进行充分灌溉。利用石膏块土壤水分传感器和中子仪分别测量了根区土壤水势和土壤含水量的变化，并实测了果实生长量、枝条生长量和产量。利用水量平衡法得出了在上述两种滴灌条件下桃树不同生育期的日均耗水量与蒸发皿系数。与充分灌比较，调亏灌溉对产量没有影响，灌水量减少了32%，并有效抑制了枝条生长。     

Evaluation of Crop Models for Simulating and Optimizing Deficit Irrigation Systems in Arid and Semi-arid Countries Under Climate Variability

The variability of fresh water availability in arid and semi-arid countries poses a serious challenge to farmers to cope with when depending on irrigation for crop growing. This has shifted the focus onto improving irrigation management and water productivity (WP) through controlled deficit irrigation (DI). DI can be conceived as a strategy to deal with these challenges but more knowledge on risks and chances of this strategy is urgently needed. The availability of simulation models that can reliably predict crop yield under the influence of soil, atmosphere, irrigation, and agricultural management practices is a prerequisite for deriving reliable and effective deficit irrigation strategies. In this context, this article discusses the performance of the crop models CropWat, PILOTE, Daisy, and APSIM when being part of a stochastic simulation-based approach to improve WP by focusing primarily on the impact of climate variability. The stochastic framework consists of: (i) a weather generator for simulating regional impacts of climate variability; (ii) a tailor-made evolutionary optimization algorithm for optimal irrigation scheduling with limited water supply; and (iii) the above mentioned models for simulating water transport and crop growth in a sound manner. The results present stochastic crop water production functions (SCWPFs) that can be used as basic tools for assessing the impact on the risk for the potential yield due to water stress and climate variability. Example simulations from India, Malawi, France and Oman are presented and the suitability of these crop models to be employed in a framework for optimizing WP is evaluated.     

Optimizing Reservoir Operation Policy Using Chance Constraint Nonlinear Programming for Koga Irrigation Dam,Ethiopia

One of typical problems in water resources system modeling is derivation of optimal operating policy for reservoir to ensure water is used more efficiently. This paper introduces optimization analysis to determine monthly reservoir operating policies for five scenarios of predetermined cropping patterns for Koga irrigation scheme, Ethiopia. The objective function of the model was set to minimize the sum of squared deviation (SSD) from the desired targeted supply. Reservoir operation under different water availability and thresholds of irrigation demands has been analyzed by running a chance constraint nonlinear programming model based on uncertain inflow data. The model was optimized using Microsoft Excel Solver. The lowest SSD and vulnerability, and the highest volumetric reliability were gained at irrigation deficit thresholds of 20 % under scenario I, 30 % under scenario II, III and V, and at 40 % under scenario IV when compensation release is permitted for downstream environment. These thresholds of deficits could be reduced by 10 % for all scenarios if compensation release is not permitted. In conclusion the reservoir water is not sufficient enough to meet 100 % irrigation demand for design command areas of 7,000 ha. The developed model could be used for real time reservoir operation decision making for similar reservoir irrigation systems. In this specific case study system, attempt should be made to evaluate the technical performance of the scheme and introduce a regulated deficit irrigation application.     

Irrigation Scheduling Optimization for Cotton Based on the AquaCrop Model

To improve irrigation efficiency, it is important to optimize agriculture irrigation scheduling. The objectives of this study were to evaluate the AquaCrop model for its ability to simulate cotton in the North China Plain and optimize irrigation strategies. The AquaCrop model was calibrated using 2002–2009 data and validated using 2010–2014 data. Root mean square error (RMSE), mean absolute error (MAE) and residual coefficient method (CRM) were used to test the model performance. The model calibrated for simulating cotton yield had a prediction error statistic RMSE of 0.152 t hm^?2, MAE of 0.123 t hm^?2 and CRM of 0.120. On validation, the RMSE was 0.147 t hm^?2, MAE was 0.094 t hm^?2 and CRM was 0.092. The goodness-of-fit values for the calibration and validation data sets indicated that the model could be used to simulate cotton yield. The analysis of irrigation scenarios indicated that the highest irrigation water productivity could be obtained by applying one irrigation at the seedling stage in a wet year, two irrigations, at the seedling and squaring stages, in a normal year and three irrigations, at the seedling, squaring and flowering stages, in a dry year. These results could be useful to the government in determining reasonable, well-timed irrigation for agricultural regions.

     

作物需水量与灌溉制度模拟

从作物需水量的基本概念出发，以水量平衡原理为基础，建立了模拟农田根层土壤水循环的计算机模型-ISAREG.这一模型具有多种功能，可模拟根层土壤水分变化，评价给定的灌溉制度，计算作物需水量和灌溉需水量，也可用以制订多种供水限制条件下的优化灌溉制度．用望都灌溉试验站的小麦、玉米、棉花3种作物两年的试验观测资料对上述模型进行了验证．     

Quantifying the Poorly Known Role of Groundwater in Agriculture: the Case of Cyprus

Agriculture in the Mediterranean region is constrained by limited water resources and in many countries irrigation demand exceeds the renewable water supply. This paper presents a comprehensive approach to (a) quantify the consumptive green (soil moisture provided by precipitation) and blue (irrigation) water use for crop production, (b) distinguish the contribution of groundwater to irrigation supply and (c) estimate groundwater over-abstraction. A spatiotemporally explicit soil water balance model, based on the FAO-56 dual crop coefficient approach, which includes the computation of evaporation losses of the different irrigation systems, was applied to the 5,760-km² area of the Republic of Cyprus for the agro-meteorological years 1995–2009. The model uses national agricultural statistics, community-level data from the agricultural census and daily data from 34 meteorological stations and 70 precipitation gauges. Groundwater over-abstraction is quantified per groundwater body, based on the sustainable abstraction rates specified in the Cyprus River Basin Management Plan, as prepared for the EU Water Framework Directive. It was found that, on average, total agricultural water use was 506 Mm³/year, of which 62 % is attributed to green water use and 38 % to blue water use. Groundwater contributed, on average, 81 % (151 Mm³/year) to blue water use and exceeded the recommended abstraction rates by 45 % (47 Mm³/year). Even though the irrigated area decreased by 18 % during the 2008 drought year, relative to the wettest year (2003), total blue water use decreased by only 1 %. The limited surface water supply during the driest year resulted in a 37 % increase in groundwater use, relative to the wettest year, and exceeded the sustainable abstraction rate by 53 % (55 Mm³/year). Overall, the model provides objective and quantitative outcomes that can potentially contribute to the improvement of water resource management in Mediterranean environments, in the light of climate change and expected policy reforms.     

覆膜棉花调亏灌溉模式的研究

调亏灌溉是一种新的作物节水灌溉技术.研究针对新疆棉花覆膜灌溉的实际,在新疆石河子乌兰乌苏农业气象站进行了棉花调亏灌溉试验研究,研究了不同灌水模式下棉花的生长状况和产量,提出了棉花的调亏灌溉模式.     

宁夏扬黄灌区玉米限额补充灌溉制度研究

结合宁夏中部干旱补灌区限额供水的特点,集成覆盖保墒技术、大田微集水技术、限额补充灌溉技术,开展玉米限额灌溉制度试验研究。综合分析作物需水关键期、限额灌溉技术、土壤含水率、产量、水分利用效率,提出宁夏中部干旱区适宜的玉米限额灌溉制度。     

鲜食葡萄无核白滴灌水肥一体化试验研究

通过鲜食葡萄无核白水肥一体化试验研究发现,果实膨大期耗水模系数达到50%以上,是鲜食葡萄需水关键期;低氮水平下,鲜食葡萄前期轻度亏水后在后期复水能够刺激新稍分化生长,充分供水条件下较高的施氮水平能够促进葡萄LAI的生长;充分供水条件下高氮有利于葡萄产量的进一步提高,重度亏水下高氮对葡萄产量积累最为不利;轻度亏水能够在保证产量的基础上提高葡萄WUE。     

节水控盐灌溉制度的优化设计

本文根据作物水盐动态响应函数，分析了作物生长与土壤水盐运动关系，建立了节水、控盐、高产灌溉制度优化设计模型，为节水灌溉和微咸水利用提供了决策依据。实例分析表明，本文提供的模型及方法是合理的；实施节水、控盐灌溉制度能带来明显的经济效益和环境效益。