生态模型在农田蒸散及土壤水分模拟中的适用性评价

为评价生态模型在农田蒸散及土壤水分运动模拟中的适用性,利用2013—2015年南京农业气象测站观测数据,评估了BEPS(Boreal Ecosystem Productivity Simulator)模拟冬小麦农田生态系统逐日蒸散及与土壤水分动态的可靠性,并进一步开展了植被冠层蒸腾和农田土壤蒸发分离。模拟结果表明:BEPS适用于研究冬小麦农田蒸散量及土壤水分运动规律;由于考虑了叶片聚集指数和冬小麦根系垂直分布递减系数随生育期变动的参数化改进,BEPS分别可以解释2013—2014年和2014—2015年两个生长季农田生态系统蒸渗仪实测蒸散量变化的83%和74%,参数化改进前后模型效率ME相当(前:0.8,后0.74),标准差RMSE(前:1.50,后1.05),平均偏差MBE(前:0.5,后0.35),误差减小;两个生长季中,土壤蒸发占冠层上方总蒸散的比例随生育进程而变化,全生育期发散比平均值分别为34%和29%;BEPS模拟的0~40 cm土层深度土壤水分随时间变化趋势与实测值基本一致,可以解释78%以上的土壤水分实测值变化,并能快速地响应降水变化。本研究表明,生态模型可以用于模拟冬小麦农田蒸散和土壤水分变化,并有助于厘定农田冠层中难以区分的植被蒸腾和土壤蒸发的比例关系,可为进一步开展气候变化背景下的区域蒸散发评估及与之相联系的农田节水管理奠定基础。     

SIMULATING SEASONAL AND INTERANNUAL VARIATIONS OF ECOSYSTEM EVAPOTRANSPIRATION AND ITS COMPONENTS IN INNER MONGOLIA STEPPE WITH VIP MODEL

 利用内蒙古羊草草原(Leymus chinensis)生态系统通量观测站的气象数据、野外实测和MODIS叶面积指数(Leaf area index, LAI), 应用基于生态系统过程的VIP(Vegetation interface process)模型, 以半小时为步长, 模拟分析了羊草草原生态系统2003～2005年(分别为平水年、平水年和干旱年)蒸散及其分量的变化过程。通过与通量数据对比, VIP模型能够很好地模拟羊草草原生态系统的蒸散过程(R² = 0.80), 在峰值大小和变化趋势上, 模拟值与实测值有较好的一致性。模拟结果显示: 3年蒸散量分别为337、338和223 mm; 在降水相对充沛的2003和2004年, 蒸腾量为192和171 mm, 而降水相对较少的2005年, 蒸腾量仅为96 mm; 年平均蒸腾和蒸发对蒸散的贡献基本持平; 生长季蒸散占全年的83%, 6月开始, 蒸腾大于蒸发, 蒸散和蒸腾的月总值均在7、8月达到最大值,两月蒸散占全年的43%。LAI是影响蒸散的主要因素, 其次是降水, 而净辐射对蒸散的影响较小。在生长季, 蒸发的季节变化平缓, 蒸散的差异主要体现在蒸腾的差异。     

黑河流域高寒草甸生态系统水分收支及蒸散发拆分研究

水分收支是对水循环要素降水、蒸发蒸腾、径流以及土壤贮储水量变化等的定量刻画,对水资源的可持续开发及利用至关重要。基于黑河流域阿柔观测站2014和2015年水文气象观测数据,运用水量平衡理论,定量的评估了高寒草甸生态系统的水分收支动态,并结合双源模型对高寒草甸生态系统蒸散发(植被蒸腾和土壤蒸发)进行拆分及评价。研究结果表明(1)在生长季(5—9月)植被蒸腾是高寒草甸生态系统主要的耗水形式,2014和2015年生长季平均蒸散比(T/ET)分别为0.74和0.79;(2)土壤水分的剧烈变化主要发生在0—40 cm处,且受冻融过程影响显著;(3)在降水较多的年份(2014)高寒草甸生态系统水分收支基本平衡,且不受冻融影响的月份(6—9)有地表径流产生约42 mm;在正常年份(2015),生态系统呈现水分亏缺,亏缺量约为134 mm,6—9月约亏缺26 mm;(4)模型估算蒸散发(ET)与实测蒸散发具有很好的一致性,相关系数可达0.90,敏感性分析表明模型输入变量对蒸散发(ET)及蒸散比(T/ET)产生的误差较小,双源模型可以很好地实现对高寒草甸生态系统蒸散发(ET)的拆分。     

气候变化对长白山阔叶红松林冠层蒸腾影响的模拟

应用基于过程的碳水耦合多层模型对长白山阔叶红松林冠层蒸腾量进行了模拟和模型验证,并模拟了冠层蒸腾量对未来气候变化的响应.结果表明:多层模型可以较好地模拟长白山阔叶红松林冠层蒸腾量,模拟值与涡动相关技术观测的实测值拟合较好.冠层蒸腾对气候变化响应的模拟显示,气温升高,潜热通量(LE)增加;土壤含水量减少,LE减少;大气CO2浓度增加,LE减少.在研究假定的气候变化情景下,LE对0～20 cm土壤含水量减少10%、CO2浓度增加190μmol·mol-1的联合变化的响应最敏感,对气温增加3.6℃、土壤含水量减少10%的联合变化的响应不敏感.     

中亚热带人工针叶林对未来气候变化的响应

利用基于生理生态学过程的EALCO模型,探讨了千烟洲中亚热带人工针叶林生态系统对未来气候变化的响应.结果表明:CO₂浓度、温度和降水的变化对该人工林生态系统碳水通量影响的程度不同,其中CO₂浓度＞温度＞降水.CO₂浓度是生态系统总光合生产力(GPP)的主要驱动因子,温度与CO₂浓度均是控制生态系统呼吸的主要环境因子,温度的升高使植物地上部分呼吸明显增加,而CO₂浓度升高则对土壤呼吸影响较大.温度升高使蒸散(ET)增加,而CO₂浓度升高则使ET减少.在未来气候变化情景(2100年)下,该人工林生态系统的净初级生产力将增加22%,说明其仍具有较强的固碳潜力.     

基于改进SW模型的千烟洲人工林蒸散组分拆分及其特征

蒸散组分拆分是准确评估陆地生态系统生产力以及估算水分利用效率的重要基础。利用改进后的Shuttleworth-Wallace模型,将蒸散拆分为植被蒸腾、土壤蒸发和冠层截留蒸发,并采用Monte Carlo随机参数化方案对模型参数进行优化。将模型与千烟洲亚热带人工针叶林站点的2011年涡度相关及小气候观测资料结合,对千烟洲人工林蒸散及其组分进行模拟。研究结果表明:半小时尺度上蒸散量模拟值与实测值的一致性在晴天和雨天都较高。半小时尺度上全年蒸散模拟值与实测值的决定系数、均方根误差和平均偏差为0.73、1.55 mmol m~(-2)s~(-1)和0.21 mmol m~(-2)s~(-1)。蒸散是该生态系统水分输出的最主要贡献项,占全年降水的80%。在蒸散中,植被蒸腾约占总蒸散量的85%,可推测2011年千烟洲人工林生态系统有较高的水分利用效率。该生态系统的蒸腾量季节变化明显,主要受饱和水汽压差和气温两种环境因素以及植被的叶面积指数影响且与三者均呈正相关;土壤蒸发约占总蒸散量的5%,季节变化平缓;模拟的冠层截留蒸发量约占总蒸散量的10%,季节变化大,与降水量呈正相关,与暴雨频次呈负相关,说明冠层无法有效截留强降水。该模型参数较少、时间分辨率高且可以有效模拟蒸散及其组分特征,是陆地生态系统水分循环过程研究有力的模型工具。     

温带阔叶红松林生态系统潜热通量模拟——气孔导度组合模型在Shuttleworth-Wallace双源模型中的应用

叶片水平的气孔导度组合模型已被成功扩展到冠层水平,并被应用于冬小麦生态系统潜热通量的模拟研究,但该研究仅基于1a的数据,有必要研究模型在更长时间尺度和其它生态系统类型的适用性.以长白山阔叶红松林(CBS)为研究对象,将组合模型进一步应用于Shuttleworth-Wallace双源模型,模拟了CBS 3a生长季内的潜热通量,利用涡度相关系统观测的潜热通量数据对模型进行验证,并对比了双源模型与单源模型的模拟结果.结果显示,双源模型较单源模型能取得更高的模拟精度,生长季不同时期的潜热通量模拟值和实测值的日变化较一致.对双源模型模拟值和实测潜热通量的相关分析显示,二者直线回归斜率和R2分别为0.96和0.72.对长白山阔叶红松林生态系统的蒸散和植被蒸腾的季节和年际变异分析发现,影响冠层蒸散和植被蒸腾季节动态的主要因素是饱和差和辐射,而影响它们年际动态的主要因素则是饱和差和温度.     

毛乌素沙地油蒿-杨柴灌丛生态系统蒸散组分分配及其影响因子

蒸散发(ET)是生态系统水分循环和能量流动的重要组成部分,准确估算ET及其各组分,对认识生态生理过程对水分平衡和植物水分利用策略的影响具有重要意义。本研究于2019年5月20日至9月15日,利用涡度相关技术和微型蒸渗仪对毛乌素沙地油蒿-杨柴灌丛生态系统ET、蒸发(E)和蒸腾(T)进行测定和估算,量化了油蒿-杨柴灌丛生态系统ET组分,并分析ET及其组分的季节特征及影响因素。结果表明: T为毛乌素沙地油蒿-杨柴灌丛生态系统生长季ET的主要组分,T/ET为53.1%。T/ET值随降水减少而升高,E/ET值随降水减少而减少,蒸散组分分配主要受降水调控。在季节尺度上,E与10 cm深处土壤含水量(SWC₁₀)和太阳净辐射(R_n)呈显著正相关,其中,SWC₁₀是E的主要影响因素;T随R_n和叶面积指数(LAI)的升高而升高,随30 cm处土壤含水量(SWC₃₀)的升高呈先升高后降低的单峰趋势,受到SWC₃₀、R_n和LAI的共同影响;水分是ET的主要影响因素。生长季蒸散/降水量(ET/P)为109.2%,5月ET/P为250.5%,表明生长季初期ET耗水部分来自非生长季降水。     

西北黑河中游荒漠绿洲农田作物蒸腾与土壤蒸发区分及作物耗水规律

利用中国生态系统研究网络临泽内陆河流域研究站绿洲农田2009年小气候、湍流交换、土壤蒸发和叶片气孔导度等综合观测试验数据,应用Shuttleworth-Wallace(S-W)双源模型以半小时为步长估算了绿洲农田玉米生长季实际蒸散量,并利用涡动相关与微型蒸渗仪实测数据对田间蒸散发量和棵间土壤蒸发量计算结果进行了检验。结果表明:S-W模型较好地估算研究区的蒸散量,并能有效区分农田作物蒸腾和土壤蒸发;全生育期玉米共耗水640 mm,其中作物蒸腾累积量为467 mm,土壤蒸发累积量为173 mm,分别占总量的72.9%和27.1%;日时间尺度上,作物蒸腾和土壤蒸发分别在0—6.3 mm/d和0—4.3 mm/d之间变化,其日平均分别为2.9和1.0 mm/d;田间供水充足,作物蒸腾与土壤蒸发比值明显受作物生长过程影响,播种—出苗期、出苗—拔节期、拔节—抽雄期、抽雄—灌浆期、灌浆—成熟期,其比值分别为0.04、0.8、7.0、5.2和1.4,不同阶段的比值差异主要受叶面积指数影响。     

基于Shuttleworth-Wallace模型的科尔沁沙地流动半流动沙丘蒸散发模拟

陆面蒸散发在气候调节和维持区域水量平衡中起关键作用.量化蒸散发及其各组分项,对深刻揭示干旱半干旱地区的生态水文过程具有重要意义.本研究基于科尔沁沙地流动半流动沙丘2017年生长季气象监测系统的原位监测数据,利用Shuttleworth-Wallace(S-W)模型对沙丘蒸散发进行模拟,在此基础上,对蒸散各组分进行拆分,并利用涡度相关对模拟蒸散发值进行验证.结果表明: 整个生长季模型模拟蒸散发值为308 mm,涡度相关实测值为296 mm,偏差较小,证明S-W模型适用于该地区的蒸散发模拟.蒸散发整体呈生长旺盛期>生长后期>生长初期,分别为192、71和45 mm,分别占总量的62.3%、23.1%和14.6%.日尺度上模型模拟值与实测蒸散发值一致性较高,模型模拟精度大体表现为: 晴天>阴天>雨天,且阴雨天模型模拟值较涡度相关实测值偏低.经拆分,土壤蒸发和植被蒸腾分别为176和132 mm,分别占总量的57.1%和42.9%,表明沙地水分利用效率较低.持续干旱和降水后,蒸散发规律明显不同,且土壤蒸发对降水的敏感性强于植被蒸腾.     

Interannual Invariability of Forest Evapotranspiration and Its Consequence to Water Flow Downstream

Although drought in temperate deciduous forests decreases transpiration rates of many species, stand-level transpiration and total evapotranspiration is often reported to exhibit only minor interannual variability with precipitation. This apparent contradiction was investigated using four years of transpiration estimates from sap flux, interception–evaporation estimates from precipitation and throughfall gauges, modeled soil evaporation and drainage estimates, and eddy covariance data in a mature oak-hickory forest in North Carolina, USA. The study period included one severe drought year and one year of well above-average precipitation. Normalized for atmospheric conditions, transpiration rates of some species were lower in drought than in wet periods whereas others did not respond to drought. However, atmospheric conditions during drought periods are unlike conditions during typical growing season periods. The rainy days that are required to maintain drought-free periods are characterized by low atmospheric vapor pressure deficit, leading to very low transpiration. In contrast, days with low air vapor pressure deficit were practically absent during drought and moderate levels of transpiration were maintained throughout despite the drying soil. Thus, integrated over the growing season, canopy transpiration was not reduced by drought. In addition, high vapor pressure deficit during drought periods sustained appreciable soil evaporation rates. As a result, despite the large interannual variation in precipitation (ranging from 934 to 1346 mm), annual evapotranspiration varied little (610–668 mm), increasing only slightly with precipitation, due to increased canopy rainfall interception. Because forest evapotranspiration shows only modest changes with annual precipitation, lower precipitation translates to decreased replenishment of groundwater and outflow, and thus the supply of water to downstream ecosystems and water bodies.     

Crop row spacing and its influence on the partitioning of evapotranspiration by winter-grown wheat in Northern Syria

A study was conducted during the 1996–97 crop growth season at ICARDA in northern Syria, to investigate the influence of wheat canopy architecture on the partitioning of moisture between soil evaporation and crop transpiration, on a soil with high hydraulic conductivity. The study was conducted on the long-term two course wheat-lentil rotation trial, established on a swelling clay soil (Calcixerollic xerochrept). The wheat canopy architecture was manipulated by sowing the crop at either of two row-spacings, 0.17 or 0.30 m, both at a constant sowing rate equivalent to 120 kg ha^–1. In this study, evapotranspiration from the crop was inferred from changes in soil moisture content over time, evaporation and rainfall interception were measured daily using microlysimetry, drainage was estimated as being the difference between potential daily evapotranspiration, and the evapotranspiration estimated from the soil water deficit. Between sowing and day 80 (tillering stage), evapotranspiration was calculated to consist mainly of soil evaporation. However, after day 80, transpiration became an increasingly dominant component of evapotranspiration. For both row-spacings, cumulative evapotranspiration over the season was approximately 373 mm. In the narrow-row crop, transpiration and soil evaporation were approximately 185 mm and 183 mm of water respectively. Conversely for the wide row-spaced crop, 172 mm of water was transpired while about 205 mm of water evaporated from the soil surface. While green leaf area index did not differ between row-spacings, the architecture of the crops as a result of sowing affected solar radiation penetration such that more incident radiation was intercepted at the soil surface of the wide row-spaced crop. This is likely to have made some contribution to the elevated levels of evaporation from the soil beneath the canopy of the wide-sown crop.     

Influence of mulching on the pattern of growth and water use by spring wheat and moisture storage on a fine textured soil

Eight tonnes ha^–1 of stubble were used to mulch spring wheat (Triticum aestivum) on a fine textured soil with the aim of controlling both transpiration and soil evaporation during the wet pre-anthesis phase to increase moisture supply during grain filling in the eastern wheatbelt of Western Australia. Mulching reduced leaf area per plant by reducing the culm number; consequently the green area index was reduced. Reduced culm number was associated with low soil temperature which at 50 mm depth averaged 7°C lower under the mulched crop relative to the control crop in mid-season. The smaller canopies of the mulched crop used 15 mm less water than those of the control before anthesis; this difference in water-use was due equally to reduced transpiration and soil evaporation. However, the mulched crop was unable to increase ET during grain filling, a response associated with the persistence of low soil temperature for most of the growth period. Hence, total ET for the season was significantly lower (18 mm) under the mulched crop than the control crop. At harvest, mulching did not have significant effects on total above-ground dry matter and grain yields, but it increased water use efficiency for grain yield by 18%, grain weight by almost 17% and available moisture in both uncropped and cropped plots by an average of 43 mm.To determine whether there was any residual effects of soil treatment on moisture storage during the summer fallow period, soil moisture was monitored both in cropped plots and uncropped plots, that were either mulched or unmulched during the growing season, from harvest in October 1988 until next planting in June 1989. Available moisture at next planting was correlated with moisture storage at harvest despite the differences in run-off, soil evaporation and fallowing efficiency (increase in moisture storage as a percentage of rainfall) between treatments during fallowing. Therefore, the mulched treatments had more moisture available (30 mm), mostly as a result of less water use during cropping in the previous growing season, than the unmulched treatment.The study shows that mulching may be used to restrain both transpiration and soil evaporation early in the season to increase availability of soil moisture during grain filling. Secondly, mulching during the previous growing season had little effect on soil moisture during the summer fallow period, however, the moisture saved by mulching during cropping was conserved for the following season. These results indicate the importance of evaluating mulching of winter crops in terms of crop yield in the subsequent growing season as well as in the current season in which the soil was treated.Abbreviations D through drainage - DAS days after sowing of the crop on 31 May 1988 - DM dry matter produced in the above-ground portion of the crop (kg ha^–1) - E₀ evaporation from Class A pan (mm) - E_s evaporation from uncropped soil (mm) - E_sc evaporation from soil beneath the wheat canopy (mm) - ET evapotranspiration (mm) - FE fallowing efficiency (gain in soil moisture storage/rainfall) - GAI green area index (area of green vegetation per unit land area) - GWUE water-use efficiency for grain production (grain yield/total ET, kg ha^–1mm^–1) - K extinction coefficient (see equation 1) - RO run-off of moisture from soil surface during/following rainfall (mm) - SM available soil moisture (mm) at harvest (SMh) or at planting (SMp) - WUE water-use efficiency for total above-ground dry matter yield (see GWUE)     

华北落叶松人工林蒸散及产流对叶面积指数变化的响应

定量评价林地蒸散和产流等水文过程对冠层叶面积指数(LAI)的响应,对于深入认识森林植被的生态水文过程及其发生机制,实现半干旱区林水综合管理和区域可持续发展是非常必要的。应用集总式生态水文模型BROOK90,模拟分析了不同降水年型(丰水年、平水年、枯水年)下,位于半干旱区的宁夏六盘山叠叠沟小流域内华北落叶松(Larix principis-rupprechtii)人工林的水文过程对冠层LAI变化的响应关系。结果发现:林分总蒸散量、冠层截留量、蒸腾量与LAI都呈显著的正相关关系(R~20.99,P0.01),而土壤蒸发量、产流量则与LAI均呈显著的负相关关系(R~20.99,P0.01);在不同的降水年型下,各水文过程变量与LAI的关系都可以很好地用指数函数来表达,且都存在着一个LAI阈值。当LAI低于阈值时,各水文过程变量随LAI的变化幅度较大;但高于阈值时,各变量的变化十分缓慢并趋于稳定。在不同降水年型下,各变量LAI阈值之间存在着一定的差异。一般地,丰水年各变量的LAI阈值要大于枯水年,尤其是冠层截留和土壤蒸发。在丰水年,各水文过程变量随LAI增加而变化的速率要比在平水年、枯水年更快,说明在水分充足年份中各变量的波动更多取决于LAI变化,而在水分亏缺的年份中则可能更多地受到水分条件的限制。模拟结果表明,通过减少冠层LAI(如间伐)导致的林分的降低蒸散耗水和增加产流的作用是有限的,这是由于林分蒸散降低的幅度要比LAI降低的幅度小。例如,在平水年,当LAI从4.2变为2.0(减少幅度52.4%)时,林分年蒸散仅从357.2 mm减少至333.9 mm(减少幅度6.5%)。     

基于树干液流及涡动相关技术的葡萄冠层蒸腾及蒸散发特征研究

针对西北干旱区绿洲经济作物葡萄树冠层蒸腾及蒸散发特征的相关问题,在甘肃省敦煌市南湖绿洲开展无核白葡萄树液流速率及蒸散发观测试验,采用基于热平衡原理的包裹式茎流计,详细分析了典型生长季7—9月份葡萄树蒸腾耗水规律,使用"单位叶面积上的平均液流速率SF×叶面积指数LAI"的方法,实现了从单株到林分冠层蒸腾的尺度扩展,并通过与涡动相关技术所测蒸散发数据对比,详细研究了葡萄地冠层蒸腾及蒸散发规律。结果表明:典型生长季中葡萄树液流速率日变化为单峰型曲线,日均耗水量从2.76 kg到10 kg不等,胸径越大的葡萄树日均耗水量越大;冠层蒸腾及蒸散发日变化曲线亦为单峰型,白天8:00—12:00与17:00—20:00期间,葡萄冠层蒸腾与蒸散发曲线均比较吻合,该时间段葡萄地蒸散发绝大部分来源于葡萄冠层蒸腾,而12:00—17:00之间由于午后太阳辐射强烈土壤蒸发量增加,葡萄蒸散发大于冠层蒸腾;典型生长季3个月中,葡萄冠层蒸腾量的变化范围在1.88—8.12 mm/d之间,日均冠层蒸腾量为6.12 mm/d,蒸散发在1.74 mm/d至10.78 mm/d之间,日均蒸散发量为7.13 mm/d;日均土壤蒸发量约为1.01 mm/d,只占总蒸散发量的14.2%,日均冠层蒸腾占日均蒸散发的比重达到85.8%,说明该生长阶段冠层蒸散发以作物蒸腾为主。     

不同时间尺度下华北落叶松人工林冠层蒸腾与环境因子的关系

在半干旱区连续2年监测华北落叶松(Larix principis-rupprechtii)的树干液流、气象因子和土壤体积含水量,分析不同时间尺度下人工林冠层蒸腾与环境因子的关系。结果表明：不同时间尺度下,华北落叶松人工林冠层蒸腾的季节变化均呈单峰曲线,即先增大后减小的趋势;2016年、2017年日蒸腾量分别为1.58 mm/d和1.71 mm/d,生长季蒸腾总量分别为241.30 mm和260.97 mm。在日尺度下,气温、太阳辐射强度和饱和水汽压差是影响华北落叶松人工林冠层蒸腾主要环境因子;月尺度下,气温、风速、降水和土壤水分是冠层蒸腾的主要影响因子;冠层蒸腾与降水、大气相对湿度的相关关系由日尺度下的负相关到月尺度的正相关,相关性增强。总体来看,随时间尺度由小到大,气温、风速、大气相对湿度、降水、土壤水分对冠层蒸腾的影响作用增大,而太阳辐射强度、饱和水汽压差的作用减弱;在未来增温增雨趋势下,研究区生长季将延长,华北落叶松人工林冠层蒸腾量可能会加大。     

Much Improved Irrigation Use Efficiency in an Intensive Wheat-Maize Double Cropping System in the North China Plain

Crop yield and water use efficiency （WUE） in a wheat-maize double cropping system are influenced by short and uneven rainfalls in the North China Plain （NCP）, A 2-year experiment was conducted to investigate the effects of irrigation on soil water balance, crop yield and WUE to improve irrigation use efficiency in the cropping system, Soil water depletion （~SWS） by crop generally decreased with the increase of irrigation and rainfall, while ASWS for the whole rotation was relatively stable among these irrigation treatments, High irrigations in wheat season increased initial soil moisture and ASWS for subsequent maize especially in the drought season, Initial soil water influenced mainly by the irrigation and rainfall in the previous crop season, is essential to high yield in such cropping systems, Grain yield decreased prior to evapotranspiraUon （ET） when ET reached about 300mm for wheat, while maize showed various WUEs with similar seasonal ET, For whole rotation, WUE declined when ET exceeded about 650 mm, These results indicate great potential for improving irrigation use efficiency in such wheat-maize cropping system in the NCP, Based on the present results, reasonable irrigation schedules according to different annual rainfall conditions are presented for such a cropping system.     

Much Improved Irrigation Use Efficiency in an Intensive Wheat-Maize Double Cropping System in the North China Plain

Crop yield and water use efficiency (WUE) in a wheat-maize double cropping system are influenced by short and uneven rainfalls in the North China Plain (NCP). A 2-year experiment was conducted to investigate the effects of irrigation on soil water balance, crop yield and WUE to improve irrigation use efficiency in the cropping system. Soil water depletion (△SWS)by crop generally decreased with the increase of irrigation and rainfall, while △SWS for the whole rotation was relatively stable among these irrigation treatments. High irrigations in wheat season increased initial soil moisture and △SWS for subsequent maize especially in the drought season. Initial soil water influenced mainly by the irrigation and rainfall in the previous crop season, is essential to high yield in such cropping systems. Grain yield decreased prior to evapotranspiration(ET) when ET reached about 300 mm for wheat, while maize showed various WUEs with similar seasonal ET. For whole rotation, WUE declined when ET exceeded about 650 mm. These results indicate great potential for improving irrigation use efficiency in such wheat-maize cropping system in the NCP. Based on the present results, reasonable irrigation schedules according to different annual rainfall conditions are presented for such a cropping system.