Evaluation of SEBS Algorithm for Estimation of Daily Evapotranspiration Using Landsat-8 Dataset in a Semi-Arid Region of Central Iran

Evapotranspiration is one the most important parameters in the hydrological cycle and plays a significant role in energy balance of the earth’s surface. Traditional field-based measurements approaches for calculation of daily evapotranspiration are valid only for local scales. Using advanced remote sensing technology, the spatial distribution of evapotranspiration may now be quantified more accurately. At the present study, daily evapotranspiration is estimated using Landsat 8 datasets based on the Surface Energy Balance System (SEBS) algorithm over the Zayanderud Dam area in central Iran. For this purpose, three Landsat 8 datasets in the years 2013, 2014 and 2015 covering the study area were atmospherically corrected using the FLAASH approach. The biophysical parameters of the earth’s surface for SEBS algorithm, such as normalized difference vegetation index (NDVI), Leaf area index (LAI), fractional vegetation cover (FC) were extracted from the visible and near infrared bands and land surface temperature was computed from thermal bands the Landsat 8 datasets. The spatial distribution of daily ET was provided separately for each year. In addition to the SEBS algorithm, the Penman-Monteith method was applied to estimate the daily ET from meteorological datasets which was obtained from two synoptic stations within the study area. Finally, the simulated daily ET values from both SEBS and Penman-Monteith method were compared to observed values obtained from a lysimeter within the study area. Although the estimated results from both SEBS and Penman-Monteith show a strong correlation with the observed values, the derived ET maps and following analysis demonstrated SEBS has higher accuracy and strength in estimation of daily ET in Zayanderud Dam region.

Responses of water productivity to irrigation and N supply for hybrid maize seed production in an arid region of Northwest China

Water and nitrogen（N） are generally two of the most important factors in determining the crop productivity. Proper water and N managements are prerequisites for agriculture sustainable development in arid areas. Field experiments were conducted to study the responses of water productivity for crop yield（WP_（Y-ET）） and final biomass（WP_（B-ET）） of film-mulched hybrid maize seed production to different irrigation and N treatments in the Hexi Corridor, Northwest China during April to September in 2013 and also during April to September in 2014. Three irrigation levels（70%–65%, 60%–55%, and 50%–45% of the field capacity） combined with three N rates（500, 400, and 300 kg N/hm^2） were tested in 2013. The N treatments were adjusted to 500, 300, and 100 kg N/hm^2 in 2014. Results showed that the responses of WP_（Y-ET） and WP_（B-ET） to different irrigation amounts were different. WP_（Y-ET） was significantly reduced by lowering irrigation amounts while WP_（B-ET） stayed relatively insensitive to irrigation amounts. However, WP_（Y-ET） and WP_（B-ET） behaved consistently when subjected to different N treatments. There was a slight effect of reducing N input from 500 to 300 kg/hm^2 on the WP_（Y-ET） and WP_（B-ET）, however, when reducing N input to 100 kg/hm^2, the values of WP_（Y-ET） and WP_（B-ET） were significantly reduced. Water is the primary factor and N is the secondary factor in determining both yield（Y） and final biomass（B）. Partial factor productivity from applied N（PFP_N） was the maximum under the higher irrigation level and in lower N rate（100–300 kg N/hm^2） in both years（2013 and 2014）. Lowering the irrigation amount significantly reduced evapotranspiration（ET）, but ET did not vary with different N rates（100–500 kg N/hm^2）. Both Y and B had robust linear relationships with ET, but the correlation between B and ET（R^2=0.8588） was much better than that between Y and ET（R^2=0.6062）. When ET increased, WP_（Y-ET） linearly increased and WP_（B-ET） decreased. Taking the indices of Y, B, WP_（Y-ET）, WP_（B-ET） and PFP_N into account, a higher irrigation level（70%–65% of the field capacity） and a lower N rate（100–300 kg N/hm^2） are recommended to be a proper irrigation and N application strategy for plastic film-mulched hybrid maize seed production in arid Northwest China.

Planting Cotton in a Crop Residue in a Semiarid Climate: Water Balance and Lint Yield

Cotton (Gossypium hirsutum L.) is planted on more land area than any other crop on the Texas High Plains. Much of this area is considered highly erodible and requires a conservation compliance program to participate in government farm programs. Because this region is semiarid and because irrigation water is increasingly limited, water conservation and efficient use of water are necessary to maximize cotton lint yields. One popular conservation compliance practice used is to plant cotton into a chemically terminated small grain crop, i.e., residue that provides wind protection to the cotton seedlings. Our hypothesis was that in a semiarid region the use of a small grain cover crop under irrigated conditions would use more water than it conserves compared to conventional tilled cotton, thus reducing cotton lint yields. To test the hypothesis separate field studies over two growing seasons and on two soil textures, a loamy fine sand and a clay loam, were conducted. The main treatments were tillage systems (conventional and conservation using terminated wheat residue). The two split plot treatments were water supply based on replacement of calculated grass reference evapotranspiration (ETo). Tillage did not affect the amount of water used by the cotton crop at either location ( 0.05) except for an 80% ETo irrigation treatment at a single location where the bare soil treatment used 10% more water than the residue treatments for both years. The residue treatment decreased (P < 0.05) cotton lint yields at both locations by 12% except for the 50% ETo single irrigation treatment in which the residue treatment yielded 14% more lint than the bare soil treatment. The use of terminated wheat residue had no impact on soil water storage during any part of the year. During a 5-month period associated with wheat growth, the wheat evapotranspiration was 20 to 40 mm more water (P < 0.05) than that lost through soil water evaporation from the conventional treatments. The use of terminated wheat residue did not benefit the water balance of the cotton crop, and was associated with decreased cotton lint yields. The results were consistent with our working hypothesis, and disproved the idea that planting cotton into wheat stubble cover increases water use efficiency.

应用ARID CROP模型对中国黄淮海地区冬小麦气候生产力的数值模拟研究

应用ＡＲＩＤＣＲＯＰ模型对黄淮海地区冬小麦气候生产力进行了数值模拟研究，给出了该地区冬小麦气候生产力Ｙｑ分布图，继而研究了水分保持最适状况时的光温生产力Ｙｗ分布状况，在此基础上给出了水分增产力Ｑ（Ｑ＝（Ｙｗ－Ｙｑ）／Ｙｑ）分布图。研究表明，黄淮海地区冬小麦气候生产力变幅在３７５０～９７５０ｋｇ／ｈｍ２之间，总的趋势北低南高，黑龙港地区出现了一个３７５０ｋｇ／ｈｍ２的低值区。水分是黄淮海北部地区冬小麦气候生产力的一个重要限制因子，当水分完全适宜时，南部淮河流域冬小麦气候生产力仅可提高５％～１０％，而黄淮海北部地区气候生产力则可提高７５％～１００％。用黄淮海地区冬小麦高产记录与生产力模拟值进行了对比分析，表明用ＡＲＩＤＣＲＯＰ模型对该地区冬小麦气候生产力进行研究是可行的，该研究为引黄灌溉提供了一定的理论依据。

Attribution analysis based on Budyko hypothesis for land evapotranspiration change in the Loess Plateau, China

Land evapotranspiration(ET) is an important process connecting soil, vegetation and the atmosphere, especially in regions that experience shortage in precipitation.Since 1999, the implementation of a large-scale vegetation restoration project has significantly improved the ecological environment of the Loess Plateau in China.However, the quantitative assessment of the contribution of vegetation restoration projects to long-term ET is still in its infancy.In this study, we investigated changes in land ET and associated driving factors from 1982 to 2014 in the Loess Plateau using Budyko-based partial differential methods.Overall, annual ET slightly increased by 0.28 mm/a and there were no large fluctuations after project implementation.An attribution analysis showed that precipitation was the driving factor of inter-annual variability of land ET throughout the study period;the average impacts of precipitation, potential evapotranspiration, and vegetation restoration on ET change were 61.5%, 11.5% and 26.9%, respectively.These results provide an improved understanding of the relationship between vegetation condition change and climate variation on terrestrial ET in the study area and can support future decision-making regarding water resource availability.

Planning for Integrative Management of Wastewater Disposal, Irrigation Water Supply and Fertilizer Use: A Case Study in an Arid Land of China

This work is a trans-disciplinary undertaking aiming at innovative water management in arid and semi-arid regions. Based on field studies on soil bacterial communities and irrigation water quality in an arid region of China where wastewater has been used for agricultural production decade long, this paper is intended to propose an integrative management scheme combining wastewater reuse in agriculture, wise use of wetlands and fertilizer management as an engine toward achieving sustainable development in arid and semi-arid regions. This study was also designed to address a key but very much neglected question about wastewater reuse in irrigation: does wastewater irrigation lead to reduction of chemical fertilizer use and increase of crop yield? Through a questionnaire, it revealed that there was a misperception among farmers about wastewater, which led to no-reduction or even increase in fertilizer use with wastewater irrigation as compared with river water irrigation. It also showed that crop yield was not increased with wastewater irrigation under the current practice. Besides, it sheds some light on an underreported health concern.

Evapotranspiration of an oasis-desert transition zone in the middle stream of Heihe River, Northwest China

As a main component in water balance, evapotranspiration is of great importance for water saving and irrigation-measure making, especially in arid or semiarid regions. Although studies of evapotranspiration have been conducted for a long time, studies concentrated on oasis-desert transition zone are very limited. On the basis of the meteorological data and other parameters（e.g. leaf area index（LAI）） of an oasis-desert transition zone in the middle stream of Heihe River from 2005 to 2011, this paper calculated both reference（ET0） and actual evapotranspiration（ETc） using FAO56 Penman-Monteith and Penman-Monteith models, respectively. In combination with pan evaporation（Ep） measured by E601 pan evaporator, four aspects were analyzed：（1） ET0 was firstly verified by Ep;（2） Characteristics of ET0 and ETc were compared, while the influencing factors were also analyzed;（3） Since meteorological data are often unavailable for estimating ET0 through FAO56 Penman-Monteith model in this region, pan evaporation coefficient（Kp） is very important when using observed Ep to predict ET0. Under this circumstance, an empirical formula of Kp was put forward for this region;（4） Crop coefficient（Kc）, an important index to reflect evapotranspiration, was also analyzed. Results show that mean annual values of ET0 and ETc were 840 and 221 mm, respectively. On the daily bases, ET0 and ETc were 2.3 and 0.6 mm/d, respectively. The annual tendency of ET0 and ETc was very similar, but their amplitude was obviously different. The differences among ET0 and ETc were mainly attributed to the different meteorological variables and leaf area index. The calculated Kc was about 0.25 and showed little variation during the growing season, indicating that available water（e.g. precipitation and irrigation） of about 221 mm/a was required to keep the water balance in this region. The results provide an comprehensive analysis of evapotranspiration for an oasis-desert transition zone in the middle stream of Heihe River, which was seldom reported before.

西北干旱区河西走廊荒漠绿洲土地覆盖类型与蒸散的关系研究——基于Landsat 8和ZY3数据融合

蒸散是地表水热平衡的重要分量,也是陆地生态过程与水文过程之间的重要纽带,尤其在干旱区地 气相互作用、碳循环、水循环等过程所包含的物质与能量交换中占有极其重要的地位。基于Landsat 8遥感影像和资源三号影像(ZY3)的高分辨率植被信息,利用SEBS模型对西北干旱区河西走廊中段临泽绿洲北部区域地表蒸散量进行了估算,并用绿洲内部和绿洲 荒漠过渡带两个通量塔涡动相关数据对模型进行评估,分析了不同土地覆盖类型对蒸散量空间分布的影响。结果表明:(1)SEBS模型模拟值与实测日蒸散值之间拟合效果较好,且在均一地表时(绿洲农田区)估算精度更高(R^2=0.96,P<0.001),RMSE、MAE分别为0.84 mm/d、0.56 mm/d;(2)从季节变化来看蒸散量与作物生长密切相关,夏季灌溉和降雨使得研究区水分充足,植被覆盖度高,蒸散量相应增加,在绿洲地区可达5.95 mm/d,而冬季最小仅为0.52 mm/d;(3)从蒸散量的空间变化来看,水体蒸散值最大,其余依次为农田、防护林、裸地和灌木丛,说明除水体外,随着植被覆盖的增大,蒸散量也逐渐增加。通过ZY3影像的高分辨率植被信息与Landsat 8影像热红外数据融合,提高了SEBS模型对该区域蒸散量的模拟效果,增进了我们对绿洲下垫面与大气间水热交换规律、水文过程、生态 水文相互作用的深入理解。

Hydrological response to land use and land cover changes in a sub-watershed of West Liaohe River Basin,China

In recent years, the streamflow of the Laohahe Basin in China showed a dramatic decrease during the rainy season as a result of climate change and/or human activities. The objective of this work was to document significant streamflow changes caused by land use and land cover （LULC） changes and to quantify the impacts of the observed changes in Laohahe Basin. in the study area, the observed streamflow has been influenced by LULC changes, dams, and irrigation from rivers, industry, livestock and human consumption. Most importantly, the growth of population and gross domestic product （GDP） accompanied by the growth in industrial and agricultural activities, which led to LULC changes with increased residential land and cropland and decreased grassland since 2000s. Statistical methods and Variable Infiltration Capacity （VIC） hydrological model were used to estimate the effects of climate change and LULC changes on streamflow and evaportranspiration lET）. First, the streamflow data of the study area were divided into three sub-periods according to the Pettitt test. The hydrological process was then simulated by VIC model from 1964 to 2009. Furthermore, we compared the simulated results based on land use scenarios in 1989, 1999 and 2007, respectively for exploring the effect of LULC changes on the spatio-temporal distribution of streamflow and ET in the Laohahe Basin. The results suggest that, accompanied with climate change, the LULC changes and human water consumption appeared to be the most likely factors contributing to the sig- nificant reduction in streamflow in the Laohahe Basin by 64% from1999 to 2009.

Comparative productivity of Prosopis cineraria and Tecomella undulata based agroforestry systems in degraded lands of Indian Desert

Tree-crop interactions were monitored by measuring tree growth characters of Prosopis cineraria L. and Tecomella undulata L. and yields of Vigna radiata （L） in agroforestry systems in degraded lands of Indian Desert. Potential competition for resource between the trees and associated crop was analyzed by measuring soil water contents, soil organic matters and NH4-N at different depths of soil layers i.e., 0-25 cm, 25-50 cm and 50-75 cm in the experimental plots. The plots size were 16 m × 18 m （D1）, 20 m × 18 m （D2） and 32 m × 18 m （D3） with tree densities of 208, 138 and 104 trees.ha^-1 after June 2002, respectively. Results showed that tree height increased by 3% to 7% during June 2002 to June 2004. Collar diameter increased by 30% and 11% in D1, 23% and 19% in D2 and 18% and 36% in D3 plots, respectively, in P. cineraria and T. undulata in two years period. The increase in crown diameter was 9% to 18% in P. cineraria and 11% to 16% in T. undulata. Tree growth was relatively greater in 2002 than in 2003. Yield of V. radiata increased linearly from D1 to D3 plots. Lowest soil water content at 1 m distance from tree base indicated greater utilization of soil water within the tree rooting zone. Concentrations of soil organic matters and NH4-N were the highest （p〈0.05） in 0-25 cm soil layer. P. cineraria was more beneficial than T. undulata in improving soil conditions and increasing crop yield by 11.1% and thus more suitable for its integration in agricultural land. The yield of agricultural crop increased when density of tree species was appropriate （i.e., optimum tree density）, though it varied with tree size and depended upon resource availability. The result indicated bio-economic benefits of optimum density of P. cineraria and T. undulata over traditional practices of maintaining random trees in farming system in arid zones.

Comparative productivity of Prosopis cineraria and Tecomella undulata based agroforestry systems in degraded lands of Indian Desert

Tree-crop interactions were monitored by measuring tree growth characters of Prosopis cineraria L.and Tecomella undulata L.and yields of Vigna radiata(L) in agroforestry systems in degraded lands of Indian Desert.Potential competition for resource between the trees and associated crop was analyzed by measuring soil water contents, soil organic matters and NH4-N at different depths of soil layers i.e., 0-25 cm, 25-50 cm and 50-75 cm in the experimental plots.The plots size were 16 m × 18 m(D1), 20 m × 18 m(D2) and 32 m × 18 m(D3) with tree densities of 208, 138 and 104 trees·ha-1 after June 2002, respectively.Results showed that tree height increased by 3% to 7% during June 2002 to June 2004.Collar diameter increased by 30% and 11% in D1, 23% and 19% in D2 and 18% and 36% in D3 plots, respectively, in P.cineraria and T.undulata in two years period.The increase in crown diameter was 9% to 18% in P.cineraria and 11% to 16% in T.undulata.Tree growth was relatively greater in 2002 than in 2003.Yield of V.radiata increased linearly from D1 to D3 plots.Lowest soil water content at 1 m distance from tree base indicated greater utilization of soil water within the tree rooting zone.Concentrations of soil organic matters and NH4-N were the highest(p<0.05) in 0-25 cm soil layer.P.cineraria was more beneficial than T.undulata in improving soil conditions and increasing crop yield by 11.1% and thus more suitable for its integration in agricultural land.The yield of agricultural crop increased when density of tree species was appropriate(i.e., optimum tree density), though it varied with tree size and depended upon resource availability.The result indicated bio-economic benefits of optimum density of P.cineraria and T.undulata over traditional practices of maintaining random trees in farming system in arid zones.

Crop Water Requirements in Egypt Using Remote Sensing Techniques

The common Soil in Egypt is clay soil so common irrigation system is tradition surface irrigation with 60% irrigation efficiency. Agricultural sector consumes more than 80% of water resources under surface irrigation (tradition methods). In arid and semi-arid regions consumptive use is the best index for irrigation requirements. A large part of the irrigation water applied to farm land is consumed by Evapotranspiration (ET). Irrigation water consumption under each of the physical and climatic conditions for large scale will be easier with remote sensing techniques. In Egypt, Agricultural cycle is often tow agricultural seasons yearly;summer and winter. Common summer crops are Maize, Rice and Cotton while common winter crops are Clover and Wheat. Landsat8 bands 4 and 5 provide Red (R) and Near Infra-Red (NIR) measurements and it used to calculate Normalized Deference Vegetation Index (NDVI) and monitoring cultivated areas. The cultivated land area was 3,277,311 ha in August 2013. In this paper Kc = 2 * NDVI ? 0.2 represents the relation between crop coefficient (Kc) and NDVI. Kc and Reference evapotranspiration (ETo) used to estimate ETc in Egypt. The main objective of this paper is studying the potential crop Evapotranspiration in Egypt using remote sensing techniques.

考虑生态耗水的干旱区绿洲灌溉用水效率评价指标与方法

针对现行干旱区绿洲尺度灌溉用水效率评价对生态服务效益考虑不足的问题,提出了在绿洲尺度上考虑生态耗水的灌溉用水效率评价指标和方法,并应用于宁夏引黄灌溉绿洲。结果表明:宁夏引黄灌溉绿洲农田蒸散消耗水量中的灌溉水量平均占比达74.7%,生态系统蒸散消耗水量中的灌溉水量平均占比达39.8%,灌溉水对生态系统的支撑作用显著;考虑生态耗水前后的灌溉用水效率差为0.052~0.074,占未考虑生态耗水灌溉用水效率的13.9%~16.1%,灌溉水的生态服务效益明显;提出的评价指标与方法合理可行,能客观反映干旱区灌溉用水的综合效益。

2005-2020年亚洲中部干旱区生态站月潜在蒸散量数据集

潜在蒸散表征大气蒸发能力,是衡量区域蒸发能力的重要指标,也是评价气候干旱程度变化、水资源供需平衡、植被耗水量等的关键参数。在收集中亚生态系统监测网络12个生态站和中国生态系统研究网络(CERN)11个位于西北干旱区生态站的气象观测数据基础上,经过数据质量控制与插补,采用Penman-Monteith模型计算潜在蒸散量,生成了2005-2020年亚洲中部干旱区生态站月潜在蒸散量数据集。本数据集时间序列较长、覆盖多种生态系统类型,可作为亚洲中部干旱问题研究的基础数据、模型输入数据、模拟结果验证数据等,也可为该区域水资源的合理开发与利用、生态环境保护等方面研究提供数据支撑。

2种水分条件下华北落叶松林的林下日蒸散量变化差异

【目的】探讨土壤湿度对华北落叶松Larixprincipis-rupprechtii林下日蒸散变化的影响,为理解林地蒸散适应气候变化的机制及制定林水协调管理方案提供理论基础。【方法】以宁夏六盘山半干旱区叠叠沟小流域华北落叶松人工林为对象,设置了遮断降水输入(防水处理)和自然降水输入2种处理,人为加大土壤湿度梯度,分析2种土壤湿度条件下气温、太阳辐射、降水量等因子对林下日蒸散量的影响。【结果】在8、9、10月,自然降水的林下日蒸散量分别为67.06、36.32、29.49 mm·d^(-1),防水处理分别为54.22、20.07、11.35 mm·d^(-1),各月自然降水下的日蒸散量均大于防水处理。2种水分条件的林下日蒸散量随时间进程总体呈逐渐减小趋势,且自然降水下波动大于防水处理。8—10月,2种水分条件的林下日蒸散量差值总体呈先升后降的波浪状变化,比值总体呈逐渐升高的波浪状变化;在8、9、10月,各日自然降水日蒸散量与防水处理日蒸散量之差的均值依次为0.41、0.54、0.59 mm·d^(-1),比值依次为1.29、1.91、2.74。随潜在蒸散增大,2种水分条件的林下日蒸散量差与土壤体积含水量差的比值逐渐增加。土壤湿度对林下蒸散的影响在日潜在蒸散量小于3 mm·d^(-1)时较小,在大于3 mm·d^(-1)时增大,在大于5 mm·d^(-1)时增大极为明显。【结论】2种水分条件的林下蒸散影响因子大致相同,区别为自然降水的林下日蒸散量更多受降水影响,而防水处理则更多受土壤湿度影响。未来应增加多个土壤湿度梯度对林下蒸散差异的影响研究。图7表1参28.

基于CWDI蒙冀半干旱区近60a谷子干旱时空变化特征

谷子是半干旱区的特色作物,具有耐旱稳产的特点。蒙冀半干旱区是谷子的优势产区,种植面积及总产量均居全国前列,但干旱严重威胁着该区谷子生产。为揭示干旱对谷子生长过程的影响,提高谷子生产应对干旱风险的能力,选取研究区内27个气象站点1961-2019年谷子生长季(5-9月)逐日气象数据,采用作物水分亏缺指数(CWDI)作为干旱指标,结合干旱强度、干旱频率、干旱站次比分析谷子干旱的时空变化特征。结果表明:(1)近60a,蒙冀半干旱区谷子干旱强度呈下降趋势。干旱的发生频率和站次比均随干旱等级的升高而降低。(2)在谷子各生育阶段,干旱强度和干旱频率表现为拔节期>苗期>成熟期>灌浆期>抽穗期。(3)空间分布上,研究区内谷子干旱强度和干旱频率均表现为由西北向东南逐渐降低,其中中旱、重旱和特旱的发生范围均减小。干旱强度和频率的降低有利于蒙冀半干旱区的谷子生产。

辽西半干旱区玉米产量预报方法对比研究

基于辽西半干旱区阜蒙县1986-2016年气象要素与玉米产量、发育期数据,使用产量丰歉相似年法、关键气象因子法、作物模型法开展了玉米产量预报研究,分析比较了3种产量预报方法的趋势预报正确率和定量预报准确率,结果表明,产量丰歉相似年法虽然可以实现玉米产量动态预报,但大概率法和加权分析法对玉米产量趋势的预报正确率均较低(33.3%~66.7%),其中加权平均法准确率高于大概率法的,但二者总体预报准确率都不高,且表现不稳定,不能满足业务服务需求。关键气象因子法提高了2014和2015年(生长季降水偏少年)的产量预报准确率,2年的产量预报趋势正确率为100%,产量预报准确率平均为89.5%。作物模型法随着发布预报日期的推迟,产量预报值更接近实际产量,降水正常年份预报效果好于降水偏少年份的预报效果。综上,将关键气象因子法与作物模型法相结合是准确预报半干旱区玉米产量的有效办法。两种方法相结合,对2011-2016年的产量预报准确率平均值达91.6%,能够满足业务服务需求。

中国西北旱区砂田表层土壤养分效应对连作响应的整合分析

为明确砂田表层土壤养分对连作的响应规律,深入揭示砂田性能逐年退化机理,文章基于国内外已发表的16篇相关文献的586组有效数据,借助Meta-analysis方法进行整合定量研究,定量分析覆砂1—3年农田与其他连作年限砂田(4—6年、7—9年、10—12年、13—15年、16—20年)在表层土壤水分状况(SWC)、养分特性(有机质SOM、全氮TN、全磷TP、全钾TK、碱解氮AN、速效磷AP、速效钾AK、全盐TSS)和酸碱环境(pH)方面的差异效应,系统阐释砂田表层土壤养分特性逐年变异的发生路径及驱动因素,进而综合评估其肥力水平。结果表明:伴随种植年限的增加,砂田表层土壤水分储量和养分强度整体呈现下降态势(P<0.05),4—20年的土壤SWC、SOM、TN、TP、TK、AN、AP、AK含量分别较1—3年减少39.06%、14.21%、14.96%、10.06%、8.20%、15.87%、37.01%、18.60%(P<0.05)。表层土壤SOM、TN、TP、TK、AN、AP、AK主要于10—12年开始大幅流失(P<0.05),而4—6年土壤SOM、TP、TK、AK含量的相对变化则不显著(P>0.05)。砂田在耕作12年内具有显著压盐效果,12年以后的表层土壤TSS含量则开始呈现逐年增加的发展趋向(P<0.05),其土壤pH整体增加1.29%(P<0.05)。连作年限是砂田表层土壤TN、TP和AK变异的关键因子;SWC则为土壤SOM、AP和TSS演化的主导要素。总体而言,砂田在连作10年左右即可出现明显的养分亏缺状态。因此,亟需提出科学合理的农田管理措施,以有效提升退化砂田的土壤肥力水平。

Effect of smart sprinkler irrigation utilization on water use efficiency for wheat crops in arid regions

The smart irrigation system(SIS)developed in this research is a valuable tool for scheduling irrigation and quantifying water required by plants.SIS was implemented and tested under sprinkler irrigation system to irrigate wheat crops(YecoraRojo).Results obtained from this system were compared with the control irrigation system(CIS),whose scheduling method was based on data from an automatic weather station.Results indicated significant savings in applied water using the SIS.In addition,the use of the SIS conserved 12%of irrigation water compared to CIS and obtained an economical yield.The water use efficiency(WUE)under SIS had generally higher values(1.64 kg/m^(3))compared to CIS(1.46 kg/m^(3)).Hence,the application of SIS technology provides significant advantages on WUE and irrigation water use efficiency(IWUE).Relatively high WUE and IWUE were found for the irrigation treatment(80%of evapotranspiration under SIS).Results showed that the irrigation requirements of wheat increased(100%of ETc under CIS)with increasing evapotranspiration(ETc)but excessive irrigation could decrease WUE and IWUE.These results indicated that extreme irrigation might not produce higher yield or optimal economic benefit,thus,suitable irrigation schedules by using SIS must be established and extendable to other agricultural crops.

Understanding the attributes of the dual oasis effect in an arid region using remote sensing and observational data

Investigating the attributes of the dual oasis effect and oasis–desert interactions is crucial for understanding the climatic and ecological effects of oases.In this study,oasis effect intensity(OEI)was used as an indicator to investigate the factors that contribute to the dual oasis effect.The oasis effect has two attributes:the surface oasis heating effect(OHE)occurred in winter,while the oasis cooling effect(OCE)occurred in the other three seasons,especially in summer.During the day,the OEI of the whole oasis was−12.8℃,−5.2℃,and−4.5℃ in summer,spring,and autumn,respectively,which indicated a strong OCE;and OEI was 0.5℃ in winter,which indicated a weaker OHE.In arid regions,the OCE dominated most of the time,but the OHE occurred in winter and cannot be ignored.In addition,through statistical analysis and energy balance analysis,high evapotranspiration of the oasis was the main factor leading to the occurrence of OCE in the summer,while low albedo to the occurrence of OHE in winter.