Determining placement criteria of moisture sensors through temporal stability analysis of soil water contents for a variable rate irrigation system

Developing placement criteria for soil moisture sensors is crucial in increasing the practical functionality of a variable rate irrigation (VRI) system. In this field study, the temporal stability pattern of soil water content was compared between VRI and uniform rate irrigation (URI) treatments during growing seasons of winter wheat and summer maize to determine the placement criteria of soil water sensors. The 1.64-ha experimental site located in a highly variable alluvial flood plain was divided into four management zones according to the available water holding capacity ranging from 152 to 205 mm within the 0.6 m soil profile. In each zone, two sub-zones were created to represent VRI and URI treatments. A temporal stability analysis of soil moisture was conducted by regularly measuring soil water contents at 62 locations in the field during the growing seasons. Results showed that the VRI management changed the overall similarity of soil moisture spatial patterns when crop water consumption was provided mainly by irrigation water rather than precipitation. In each management zone, every measuring position was a time-stable location with respect to the mean soil water content. Significant linear regressions were detected between the mean clay percentile in each management zone and the clay percentile representing the mean soil water content sites, and a nearly equivalent value of fitted equation coefficient was obtained for winter wheat (1.15) and summer maize (1.19). These results demonstrated that the temporal stability of soil water content spatial patterns still existed in each management zone with the VRI management, and the clay percentile supplied a priori identification for placement of soil moisture sensors.     

Prediction of plant water status in almond and walnut trees using a continuous leaf monitoring system

Persistent drought conditions in the Central valley of California demands efficient irrigation scheduling tools such as precision or variable rate irrigation (VRI). To assist VRI scheduling, an experiment was conducted in almond and walnut orchards using a sensor system called ‘leaf monitor’, which was developed at UC Davis to detect plant water status. A Modified Crop Water Stress Index (MCWSI) was calculated to quantify plant water status using leaf temperature and environmental data collected by the leaf monitor. This technique also took into account spatio-temporal variability of plant water status. Stem water potential (SWP), which is considered a standard method for determining plant water stress (PWS), was also measured simultaneously. Relationships between measured deficit stem water potential (DSWP), which is the difference between SWP and the saturated baseline, and MCWSI were developed for both crops based on data collected during the 2013 and 2014 growing seasons. A linear relationship was found in the case of walnut crop with a coefficient of determination (r²) value of 0.67. A quadratic relationship was found in the case of almonds with a coefficient of multiple determination (R²) value of 0.75. Moreover, these results highlighted that at lower PWS of below 0.5 MPa of DSWP, almonds crops did not show any decrease in transpiration rate. However, when the stress level exceeded 0.5 MPa of DSWP, transpiration rate tended to decrease. On the other hand, walnut crop showed decrease in transpiration rate even at low PWS of below 0.5 MPa of DSWP. Temporal variability was noticed in PWS as it was found that coefficients of saturation baseline used for MCWSI method changed significantly throughout the season. MCWSI values estimated before an irrigation event was used to calculate the irrigation amount for low frequency variable rate irrigation (VRI) based on the relationship found between MCWSI and DSWP, and VRI led to an average 39% reduction in water usage as compared to the fixed 100% ET replacement irrigation method for all trees. Based on the results, leaf monitor showed potential for use as an irrigation scheduling tool.

     

Soil water status mapping and two variable-rate irrigation scenarios

Irrigation is the major user of allocated global freshwaters, and scarcity of freshwater threatens to limit global food supply and ecosystem function—hence the need for decision tools to optimize use of irrigation water. This research shows that variable alluvial soil ideally requires variable placement of water to make the best use of irrigation water during crop growth. Further savings can be made by withholding irrigation during certain growth stages. The spatial variation of soil water supplied to (1) pasture and (2) a maize crop was modelled and mapped by relating high resolution apparent electrical conductivity maps to soil available water holding capacity (AWC) at two contrasting field sites. One field site, a 156-ha pastoral farm, has soil with wide ranging AWCs (116–230 mm m⁻¹); the second field site, a 53-ha maize field, has soil with similar AWCs (161–164 mm m⁻¹). The derived AWC maps were adjusted on a daily basis using a soil water balance prediction model. In addition, real-time hourly logging of soil moisture in the maize field showed a zone where poorly drained soil remained wetter than predicted. Variable-rate irrigation (VRI) scenarios are presented and compared with uniform-rate irrigation scenarios for 3 years of climate data at these two sites. The results show that implementation of VRI would enable significant potential mean annual water saving (21.8% at Site 1; 26.3% at Site 2). Daily soil water status mapping could be used to control a variable rate irrigator.     

基于WebGIS的多指标灌溉信息管理系统

【目的】提高灌溉决策精度,实现水资源的高效利用。【方法】从精确灌溉的角度出发,采用系统工程和软件工程的原理和方法,将计算机、数据库、网络技术和地理信息系统等多种技术相融合,建立了以WebGIS为基础的多指标灌溉信息管理系统。【结果】以作物需水信息为基础,综合考虑土壤、作物、田间监测、灌排信息和气象等因素的影响,构建了单指标和多指标决策模型,利用SuperMap IS.NET的网络发布功能,将灌区信息、实时气象、作物需水量、有效降雨量、决策结果、土壤墒情分布等信息进行发布,实现信息的动态可视化表达。本系统可使操作人员既能够通过地图宏观了解灌区和决策结果的总体情况,又能对离散资料进行分析和整合。【结论】系统在人民胜利渠灌区和广利灌区推广应用的结果表明,系统的应用在一定程度上提高了灌溉管理水平和决策精度, 实现了灌溉管理与决策的智能化和信息化。     

Effect of irrigation management on soil salinization in Manas River Valley, Xinjiang, China

Abstract The irrigated area of Manas River Valley in Northwest China is an example of the successful reclamation of massive land affected by shallow ground water levels and salinization. To determine the effect of irrigation management practices on soil salinization, soil profiles representing various soil types were sampled. The historical records on the characteristics of irrigation management practices, groundwater level and soil salts accumulation in this region at four key periods, namely: flood irrigation without drainage; flood irrigation with drainage but of low efficiency; irrigation in combination with lined irrigation canals and exploitation of groundwater; and irrigation with the application of water-saving irrigation techniques, were analyzed emphatically. In addition, the salinization status of cultivated land in 2010 and 2020 was also predicted by using analogism according to the relationship between soil salinization and irrigation practices. The results revealed that the application of the traditional irrigation methods, such as flood irrigation and ridge irrigation, resulted in a rapid rising of groundwater level and salts accumulation in soil surface layers. However, with the way of well irrigation and well drainage, the groundwater level and the desalinization in soil layers apparently lowered, leading to a substantial increase of crop yield. Currently, the application of drip irrigation under mulch decreased the salts concentration in soil layers and increased the crop yield. With the continuous application of drip irrigation, the average soil desalinization efficiency in soil layers may increase. It is predicted that the percentage of salinized land would be reduced to 35%–40% when irrigation water is utilized reasonably in 2010. With the high efficient utilization of irrigation water after 2020, the salinized land would remain below 30%. It is concluded that with the improvement of irrigation management, an obvious desalinization would appear in the soil surface layers and the area of salinized land in this study area would gradually narrow, but the land salinization problem would be hard to totally solve. __________ Translated from Journal of China Agricultural University, 2007, 12(1): 22–26 [译自: 中国农业大学学报]     

An integrated approach to site-specific management zone delineation

Dividing fields into a few relatively homogeneous management zones (MZs) is a practical and cost-effective approach to precision agriculture. There are three basic approaches to MZ delineation using soil and/or landscape properties, yield information, and both sources of information. The objective of this study is to propose an integrated approach to delineating site-specific MZ using relative elevation, organic matter, slope, electrical conductivity, yield spatial trend map, and yield temporal stability map (ROSE-YSTTS) and evaluate it against two other approaches using only soil and landscape information (ROSE) or clustering multiple year yield maps (CMYYM). The study was carried out on two no-till corn-soybean rotation fields in eastern Illinois, USA. Two years of nitrogen (N) rate experiments were conducted in Field B to evaluate the delineated MZs for site-specific N management. It was found that in general the ROSE approach was least effective in accounting for crop yield variability (8.0%–9.8%), while the CMYYM approach was least effective in accounting for soil and landscape (8.9%–38.1%), and soil nutrient and pH variability (9.4%–14.5%). The integrated ROSE-YSTTS approach was reasonably effective in accounting for the three sources of variability (38.6%–48.9%, 16.1%–17.3% and 13.2%–18.7% for soil and landscape, nutrient and pH, and yield variability, respectively), being either the best or second best approach. It was also found that the ROSE-YSTTS approach was effective in defining zones with high, medium and low economically optimum N rates. It is concluded that the integrated ROSE-YSTTS approach combining soil, landscape and yield spatial-temporal variability information can overcome the weaknesses of approaches using only soil, landscape or yield information, and is more robust for MZ delineation. It also has the potential for site-specific N management for improved economic returns. More studies are needed to further evaluate their appropriateness for precision N and crop management.     

A simulation model assisted study on water and nitrogen dynamics and their effects on crop performance in the wheat-maize system: (II) model calibration, evaluation and simulated experimentation

The test on the model with data collected from two years’ field experiments revealed an ability to satisfactorily simulate crop parameters such as LAI, biomass accumulation and partitioning, yield, and variables influencing crop growth and development as nitrogen uptake by crops and partitioning in different organs, and dynamics of soil water and nitrogen including infiltration and leaching. With the model, crop yield, water use efficiency (WUE), nitrogen use efficiency (NYE) and water-nitrogen leaching at specific soil layers under various water and nitrogen management practices were simulated to provide data used as references for designing sustainable nitrogen and water management practices. The outputs of the simulated experiment with various treatments of irrigation and nitrogen application indicated that crop yield was closely related to water and nitrogen application, crop water use was positively related to irrigation amount, and nitrogen fertilization could improve the crop water use and WUE within certain limits. This is a valuable evidence to be considered in water-saving farming. Nitrogen uptake had a positive relation to nitrogen application, while irrigation to some extent improved its uptake by crops and hence increased NYE. Additionally, irrigation and fertilization had great effects on nitrogen leaching. Thus, in order to improve WUE and NYE, the model showed how nitrogen application and irrigation should be well coordinated.     

新疆农田排水技术治理盐碱地的发展概况

农田排水技术是解决土壤盐渍化的重要方式之一。近年来依赖合理的农业节水技术和管理理念对耕地进行改造,地下水位逐年降低,绿洲农业的快速发展使人们产生重灌轻排的思想。然而本质上盐分并未脱离土壤,耕地存在次生盐渍化风险,农田排水技术任重道远。实践证明,长期应用农田排水技术在盐碱地改良、提高作物产量、促进农业经济发展等方面起着积极作用。对解放以来新疆农田排水技术治理盐碱化的发展及概况进行梳理和总结,指出农田排水技术在实际发展中存在的实际问题,并提出新形势下通过排水技术治理盐碱化的措施与建议,为今后新疆滴灌盐渍区土壤治理提供参考。     

A flexible approach to managing variability in grain yield and nitrate leaching at within-field to farm scales

We up-scaled the APSIM simulation model of crop growth, water and nitrogen dynamics to interpret and respond to spatial and temporal variations in soil, season and crop performance and improve yield and decrease nitrate leaching. Grain yields, drainage below the maximum root depth and nitrate leaching are strongly governed by interaction of plant available soil water storage capacity (PAWC), seasonal rainfall and nitrogen supply in the water-limited Mediterranean-type environment of Western Australia (WA). APSIM simulates the interaction of these key system parameters and the robustness of its simulations has been rigorously tested with the results of several field experiments covering a range of soil types and seasonal conditions in WA. We used yield maps, soil and weather data for farms at two locations in WA to determine spatial and temporal patterns of grain yield, drainage below the maximum root depth and nitrate leaching under a range of weather, soil and nitrogen management scenarios. On one farm, we up-scaled APSIM simulations across the whole farm using local weather and fertiliser use data and the average PAWC values of soil type polygons. On a 70 ha field on another farm, we used a linear regression of apparent soil electrical conductivity (EC_a) measured by EM38 against PAWC to transform an EC_a map of the field into a high resolution (5 m grid) PAWC map. We then used regressions of simulated yields, drainage below the maximum root depth and nitrate leaching on PAWC to upscale the APSIM simulations for a range of weather and fertiliser management scenarios. This continuous mapping approach overcame the weakness of the soil polygons approach, which assumed uniformity in soil properties and processes within soil type polygons. It identified areas at greatest financial and environmental risks across the field, which required focused management and simulated their response to management interventions. Splitting nitrogen applications increased simulated wheat yields at all sites across the field and decreased nitrate leaching particularly where the water storage capacity of the soil was small. Low water storage capacity resulted in both low wheat yields and large leaching loss. Another management option to decrease leaching may be to grow perennial vegetation that uses more water and loses less by drainage.Paper from the 5th European Conference on Precision Agriculture (5ECPA), Uppsala, Sweden, 2005     

水稻水分精确管理的知识模型研究

【目的】水稻是中国主要的粮食作物,其生长需消耗大量的水资源,因此水分精确管理对于水稻高效生产具有重要的意义。【方法】在分析和提炼水稻栽培理论与技术研究资料的基础上,通过定量描述水稻需水规律与栽培技术、品种类型、生态环境之间的动态关系,根据土壤水分平衡原理,采用土壤水势作为灌溉指标,建立水稻水分精确管理知识模型;基于系统工程思想,进一步在Microsoft Visual Studio.NET 2005平台上构建水分精确管理知识模型系统。【结果】模型具有灌溉管理方案设计以及动态调控的功能,在杭州和南京两个生态点进行的大田对比试验表明,两生态点按照模型设计方案进行水分管理的田块,其产量平均分别提高了6.9%和9.1%,灌溉水分生产率平均分别提高了53.61%和42.73%。【结论】该模型对于不同条件下的水稻水分精确管理具有较好的适用性和指导性。     

基于GSM的土壤湿度监测系统的研究

为充分利用水资源,满足农田灌溉之需,要求旱区农业从粗放的灌溉模式向集约型精量灌溉转变。作物需水状况的准确监测是实现精量灌溉和智能化农业用水管理的前提。基于GSM的土壤湿度监测系统由土壤湿度检测传感器、数据处理模块、GSM无线传输模块3部分组成。该系统采用土壤湿度传感器检测农田中的土壤湿度,单片机通过AD采集湿度信息并与设定值相比较,若湿度低于设定值,则通过GSM模块将信息发至农户,提醒用户开始灌溉。试验表明,该系统能有效监测土壤中湿度,为农户灌溉提供决策依据,实现农作物精量灌溉的远程监测。     

春季储水灌溉条件下啤酒大麦节水增产机理研究

测定了不同春季储水灌溉定额下啤酒大麦出苗率、生长发育动态、土壤水分变化、耗水规律及水分利用效率,并结合气象资料比较不同灌水处理的优越性,分析不同春季储水灌溉定额对土壤水分、降水利用及作物产量的影响。结果表明,将冬季储水灌改为春季储水灌从技术层面上切实可行;在适宜灌水定额条件下,采用春季储水灌溉技术较冬季储水灌溉技术可减少储水灌灌溉水量75 mm,减少土壤蒸发37.4%,水分利用效率提高26.2%。在实际大麦种植生产中应以春季储水灌定额75 mm,生育期灌水5次,灌水定额75 mm为宜,这样不仅可节约有限水资源,还可提高地温及水分利用效率,达到节水、增效的目的。     

土壤水分空间变异性的研究

我国北方地区水资源紧缺,而且又是农业生产较为密集的地域,因此农业节水、农田水分转化及有效利用土壤水分成为精细农业急待解决的重要问题之一。土壤水分数据采集及空间变异性的研究对于如何充分发挥土壤水分的潜力、保护水资源、加强农田水分管理、灌溉排水设计、农田墒情预报等具有深远的理论指导意义和较强的地域性、实践性的应用价值。文章应用地理信息软件ArcGIS 9.0中的Spatial Analyst模块中反距离权重插值法、样条函数内插法和克立格插值法来绘制所测土壤水分特性的空间分布图,并为进一步研究土壤水分特性与提高作物产量间的关系提供理论基础。     

Long-term impact of a precision agriculture system on grain crop production

Research is lacking on the long-term impacts of field-scale precision agriculture practices on grain production. Following more than a decade (1993–2003) of yield and soil mapping and water quality assessment, a multi-faceted, ‘precision agriculture system’ (PAS) was implemented from 2004 to 2014 on a 36-ha field in central Missouri. The PAS targeted management practices that address crop production and environmental issues. It included no-till, cover crops, growing winter wheat (Triticum aestivum L.) instead of corn (Zea mays L.) for field areas where corn was not profitable, site-specific N for wheat and corn using canopy reflectance sensing, variable-rate P, K and lime using intensively grid-sampled data, and targeting of herbicides based on weed pressure. The PAS assessment was accomplished by comparing it to the previous decade of conventional, whole-field corn-soybean (Glycine max L.) mulch-tillage management. In the northern part of the field and compared to pre-PAS corn, relative grain yield of wheat in PAS was greatly improved and temporal yield variation was reduced on shallow topsoil, but relative grain yield was reduced on deep soil in the drainage channel. In the southern part of the field where corn remained in production, PAS did not lead to increased yield, but temporal yield variation was reduced. Across the whole field, soybean yield and temporal yield variation were only marginally influenced by PAS. Spatial yield variation of all three crops was not altered by PAS. Therefore, the greatest production advantage of a decade of precision agriculture was reduced temporal yield variation, which leads to greater yield stability and resilience to changing climate.     

作物水分信息采集技术与采集设备

随着社会经济的发展和科学技术的不断进步，农田灌溉正朝着“自动、精准”的方向发展。实现自动、精准灌溉，需要获得及时、准确的作物水分状况信息作为基本依据，而先进、可靠的采集技术与设备则是快速、准确、连续获取作物水分信息的重要保障。作物水分信息，根据其采集部位可分为土壤信息和作物信息两类；而根据采集信息所代表
表的范围，则可分为点源信息和区域信息两类。2种分类结果相组合，可以将作物水分信息分为点源土壤水分状况信息，区域土壤水分状况信息，点源作物水分状况信息和区域作物水分状况信息四大类O目前应用较多的点源土壤水分状况信息快速采集技术主要有中子仪法、时域反射法（TDR）、频域反射法（FDR）、驻波率法（SWR）和张力计法；点源作物水分状况信息的采集技术则主要有红外温度法、叶水势法、光谱法、茎变差法和蒸腾速率法；区域土壤水分状况信息的采集技术主要有遥感法（裸地表层土壤）和墒墒情监测网络法；区域作物水分状况信息则主要通过遥感方法获得，包括热红外遥感和微波遥感等方法。这些技术方法各有优点、缺点和适用范围。从目前的研究和实际应用情况看，基于土壤介电特性的土壤水分信息测量技术（TDR，FD和SWR）和基于植株蒸腾速率、植株茎直径变差和作物冠层红外温度的作物水分状况信息测量技术是具有明显优优势和良好发展潜力的点源水分信息采集技术；以TDR、FDR和SWR为基础，结合GPS和GSM／GPRS无线数据传输系统，适用于区域土壤水分信息的采集；而以热红外遥感和微波遥感为基础的系统则是大面积的区域土壤水分状况信息（裸土表层）和区域作物水分状况信息的主要采集方法。这些作物水分信息采集方法的进一步完善提高，以及相应的精度高、稳定性好、价格适中的各类传感器及配套的数据处理设备的研制将是未来作物需水信息采集领域的重点工作目标。     

新疆棉花覆膜灌溉决策系统

本研究在棉花灌溉管理系统研究中采用新的中子仪标定法 ,对棉花土壤水分进行动态监测 ,通过棉花灌溉决策软件 ,考虑灌区土壤空间变异、灌水方法和地膜覆盖对土壤棵间蒸发影响等制定合理的灌溉方案 ,建立棉花灌溉决策体系 ,指导灌溉系统进行合理的灌溉 ,提高水的利用率和棉花的产量 ,并提出灌溉决策今后进一步的研究和应用方向。     

A simulation of winter wheat crop responses to irrigation management using CERES-Wheat model in the North China Plain

To improve efficiency in the use of water resources in water-limited environments such as the North China Plain(NCP), where winter wheat is a major and groundwater-consuming crop, the application of water-saving irrigation strategies must be considered as a method for the sustainable development of water resources. The initial objective of this study was to evaluate and validate the ability of the CERES-Wheat model simulation to predict the winter wheat grain yield, biomass yield and water use efficiency(WUE) responses to different irrigation management methods in the NCP. The results from evaluation and validation analyses were compared to observed data from 8 field experiments, and the results indicated that the model can accurately predict these parameters. The modified CERES-Wheat model was then used to simulate the development and growth of winter wheat under different irrigation treatments ranging from rainfed to four irrigation applications(full irrigation) using historical weather data from crop seasons over 33 years(1981–2014). The data were classified into three types according to seasonal precipitation: 100 mm, 100–140 mm, and 140 mm. Our results showed that the grain and biomass yield, harvest index(HI) and WUE responses to irrigation management were influenced by precipitation among years, whereby yield increased with higher precipitation. Scenario simulation analysis also showed that two irrigation applications of 75 mm each at the jointing stage and anthesis stage(T3) resulted in the highest grain yield and WUE among the irrigation treatments. Meanwhile, productivity in this treatment remained stable through different precipitation levels among years. One irrigation at the jointing stage(T1) improved grain yield compared to the rainfed treatment and resulted in yield values near those of T3, especially when precipitation was higher. These results indicate that T3 is the most suitable irrigation strategy under variable precipitation regimes for stable yield of winter wheat with maximum water savings in the NCP. The application of one irrigation at the jointing stage may also serve as an alternative irrigation strategy for further reducing irrigation for sustainable water resources management in this area.     

Geostatistical modelling of within-field soil and yield variability for management zones delineation: a case study in a durum wheat field

The paper proposes a geostatistical approach for delineating management zones (MZs) based on multivariate geostatistics, showing the use of polygon kriging to compare durum wheat yield among the different MZs (polygons). The study site was a durum wheat field in southern Italy and yield was measured over three crop seasons. The first regionalized factor, calculated with factorial cokriging, was used to partition the field into three iso-frequency classes (MZs). For each MZ, the expected value and standard deviation of yield were estimated with polygon kriging over the three crop seasons. The yield variation was only in part related to soil properties but most of it might be ascribable to different patterns of meteorological conditions. Both components of variation (plant and soil) in a cropping system should then be taken into account for an effective management of rainfed durum wheat in precision agriculture. The proposed approach proved multivariate Geostatistics to be effective for MZ delineation even if further testing is required under different cropping systems and management.     

灌溉方式对土壤中水分运动影响的模拟研究

在温室生产中,作物需要的水分主要依靠滴灌和喷灌方式供给,为了解在不同灌溉方式下土壤中水分运动的规律,以Navier-Stokes方程为框架、运用CFX流体动力学分析软件对滴灌和喷灌方式下水分运动情况进行了三维稳态模拟,模拟中设单位时间内供水量相同.模拟结果显示:灌溉方式对土壤中水分运动和分布有重要作用.在滴灌下,水分主要集中在作物根系区域,水分利用效率高.土壤水分呈近球状分布,随着灌溉时间的增加,球形边界逐渐模糊并向土壤深层延伸.在喷灌下,土壤水分一层层向下渗透,水分含量呈从上往下逐步递减,在每一层中的水分含量相对均一,在相同灌溉量下水分接触土壤量比滴灌时少.