Spatial analysis of long‐term effects of different tillage practices based on penetration resistance

Measuring penetration resistance (PR) is a common technique for evaluating the effects of field management on soils. This study focuses on the effects of long‐term tillage on the spatial distribution of PR, comparing reduced and conventional tillage (CT) practices. The study site, located in Lower Saxony (Germany), has been subdivided into three plots, with one plot having been managed conventionally, whereas reduced tillage (RT) practices have been applied to the other two. In total, PR was measured at 63 randomly selected points. The PR data were stepwise interpolated using kriging with external drift. Core samples have been taken at 20 additional sites. The results show significant differences in PR between the different tillage practices. Within the conventionally managed plot, PR ranges to 2.3 MPa less in the topsoil than under RT. However, measured saturated hydraulic conductivity and amount of biopores at the depth of 30–35 cm are significantly greater under RT, indicating improved soil properties under RT. Comparisons between the headlands (HL) and the inner field point out the effects of intense field traffic in the HL, where maximum PR values of about 6 MPa have been measured. The spatial prediction of PR values show that long‐term effects of different tillage practices result in clearly structured patterns between CT and RT and the HL. Combining extensive PR measurements and point measurements of additional soil properties supports an adequate interpretation of PR data and can lead to fieldwide derivation of soil functions influenced by field management.     

Simulation of statistical characteristics of gap distribution in forest stands

An estimate of the required amount of LAI-2000 or digital hemispheric image measurements to ensure the desired accuracy of the leaf area index value derived from optical analyser measurements by inversion of gap fraction data is given. The estimate is based on a theoretical model of the second order statistics of gap occurrence in forest canopies. The main attention is paid to gap fractions averaged over the angular rings similar to the LAI-2000 instrument. Nilson's (1999) forest gap fraction model is first extended to simulate the bidirectional gap fraction and next the approximate equations for the standard deviation of gap fraction, correlation matrix of gap readings in different LAI-2000 angular rings, standard deviation of the LAI value as determined by the inversion of gap fraction data are derived. The results of simulation are compared with those obtained by LAI-2000 instrument and digital hemispheric photographs in three mature forests from Järvselja, Estonia. The comparison shows an acceptable agreement between the simulated and measured second order statistical characteristics. The distance from the observation height to the crowns and crown dimensions appear to be important in determining the magnitude of variance. When the LAI-2000 instrument is used together with a view-cap, the angular size of the view-cap has an effect on the second order statistics and on the value of apparent clumping index. A computer program has been written to calculate the second-order gap statistics.     

基于遥感和地面试验的水分指数与土壤湿度及生理指标关系

为研究作物生长发育早期受干旱影响的作物水分光谱特征,对冬小麦返青期进行水分控制试验。利用野外光谱辐射仪在河北固城试验区测量冬小麦的光谱并分别计算归一化水分指数（NDWI）和简单比值水分指数（SRWI）,同时测定冬小麦的叶绿素浓度（Chl）、叶面积指数（LAI）、株高（H）和叶片相对含水率（LRWC）等冠层生理指标和土壤湿度（SM）。分析结果表明：冬小麦生理指标与土壤湿度之间有着显著的正相关,最大相关系数为0.657,表明土壤水分状况直接影响作物发育早期的光合和生长状况。NDWI/SRWI与SM相关系数均为 0.545,呈现弱的正相关;相反,水分指数与冬小麦生理指标之间的相关不明显,特别是,NDWI/SRWI与LRWC的相关系数仅为0.175。据此得出在作物低覆盖生长阶段,水分指数更多反映的是土壤水分状况而不是作物水分。     

利用可见光近红外的尾矿区农田土壤Cu含量反演

矿山开采普遍存在土壤重金属污染问题,有效的进行尾矿区农田土壤重金属含量估算迫在眉睫。以陕西金堆城矿区尾矿为研究区,采集土壤样本,测量土壤可见光近红外光谱,测试分析土壤铜元素含量。将Isomap（Isometrio mapping）和LLE（locally linear embedding）流形学习方法应用于土壤高光谱降维,基于随机森林构建估算模型,反演土壤铜含量。结果表明：降维后的高光谱数据反演精度更高,Isomap降维后模型预测结果均方根误差为30.50,R2=0.76,优于LLE降维结果。研究为尾矿区土壤Cu元素含量的快速反演估算提供了理论依据。     

Estimating energy balance fluxes above a boreal forest from radiometric temperature observations

The great areal extent of boreal forests confers these ecosystems potential to impact on the global surface-atmosphere energy exchange. A modelling approach, based on a simplified two-source energy balance model, was proposed to estimate energy balance fluxes above boreal forests using thermal infrared measurements. Half-hourly data from the Solar-Induced Fluorescence Experiment, carried out in a Finnish boreal forest, was used to evaluate the performance of the model. Energy balance closure, determined by linear regression, found all fluxes to underestimate available energy by 9% (r² = 0.94). Significance in the energy balance of the heat storage in the air and in the soil terms was also analyzed. Canopy temperatures, measured by a CIMEL Electronique CE 312 radiometer, together with ancillary meteorological variables and vegetation characteristics, were used to run the model. Comparison with ground measurements showed errors lower than ±15 W m^?2 for the retrieval of net radiation, soil heat flux and storage heat flux, and about ±50 W m^?2 for the sensible and latent heat fluxes. A sensitivity analysis of the approach to typical operational uncertainties in the required inputs was conducted showing the necessity of accurate measurements of the target radiometric surface temperature.     

基于多种光谱仪的水稻前期植株氮积累量监测

为了明确水稻穗肥施用前地上部植株氮积累量与各光谱仪冠层光谱参数的定量关系,进而为水稻精确追氮提供决策依据。基于不同品种和不同施氮水平的7个水稻田间试验,于分蘖期和拔节期利用ASD Fieldspec FR2500高光谱仪、Cropscan MSR-16多光谱仪和Greenseeker RT100主动光谱仪同时采集冠层光谱反射率,并同步取样测定地上部植株氮积累量,研究基于不同光谱仪构建的植被指数与植株氮积累量之间的关系。结果表明,部分植被指数与水稻地上部植株氮积累量关系密切,基于3种光谱仪构建的水稻地上部植株氮积累量监测模型的稳定性和适用性有较大差异。对于ASD高光谱仪,虽然基于差值植被指数（760,740）能较好估测植株氮积累量,拟合模型决定系数R2为0.79,但模型检验效果较差,其R2和均方根误差分别为0.15和2.11 g/m2;对于Cropscan多光谱仪,差值植被指数（760,710）能较好反演植株氮积累量,拟合模型的R2为0.94,模型检验的R2和均方根误差分别为0.94和0.76 g/m2;Greenseeker主动光谱仪的归一化植被指数（770,660）对地上部植株氮积累量的反演效果最好,拟合模型的R2为0.97,模型检验的R2和均方根误差分别为0.97和0.62 g/m2。研究结果可为水稻前期植株氮积累量监测过程中的光谱仪选择提供参考,为水稻精确追氮管理提供技术支撑。     

Comparing soil physical properties from continuous conventional tillage with long‐term reduced tillage affected by one‐time inversion

In addition to various positive aspects, long‐term reduced tillage may cause disadvantages such as increased weed pressure and soil compaction. Thus, single inversion tillage is customarily used for overcoming these drawbacks; however, the effects on the enhanced soil functions are unknown. The main objective of this study was therefore to assess whether improved soil physical properties following long‐term reduced tillage remain after one‐time inversion tillage by mouldboard plough. The study was undertaken on a silt loam field in Lower Saxony, Germany. Since 1996, this field has been subdivided into three treatments; one was managed conventionally using a mouldboard plough (CT), while on the others a chisel plough (RT1) and a disc harrow (RT2) were employed. In October 2014, the entire field was mouldboard ploughed. The following year, four field campaigns were conducted to compare the soil physical properties of the continuously conventional tilled plot with those affected by one‐time inversion tillage (RT1 and RT2). Dry bulk density (DBD), saturated hydraulic conductivity (Ks) and infiltration rate [K(h)] were analysed in untrafficked and trafficked areas in each plot. There were clear differences between CT and RT. At all sampling dates, both RT plots had higher Ks and K(h) compared with CT. These differences also occurred to some extent on the trafficked areas. This suggests that improved soil hydraulic properties remained after one‐time inversion tillage of a long‐term reduced tilled field. Thus, one‐time inversion tillage may offer a suitable measure for overcoming some of the main disadvantages associated with long‐term reduced tillage, while preserving the positive effects on soil physical properties.     

PAR transmittances of dry and condensate covered glass and plastic greenhouse cladding

In this study, the angular transmittances over the photosynthetically active radiation (PAR) range of two types of glass (single glass (SG) and low emissivity glass (LEG)) and three types of plastic films (low density polyethylene (LDPE), anti-drop condensation polyethylene (ADCPE) and photoselective diffusive polyethylene (DPE)) were determined experimentally in the laboratory. The measurements were performed on dry as well as on condensate covered materials, since condensate frequently occurs on a greenhouse cladding material. Based on the angular measurements, the transmittance of diffuse PAR incident on a 25° inclined slab was calculated. For the dry state, it was found that the PAR transmittance decreased with increasing photoselectivity of the materials. When covered with condensate, the PAR transmittance of the glass plates was only reduced at incidence angles higher than 15° by at most 20% on a relative scale, while the transmittance of non-anti-drop condensation films was especially reduced at small angles of incidence by at most 25%. Due to the addition of anti-drop condensation agents to a plastic film, the PAR transmittance of the film was not affected by the condensate and, therefore, showed the highest PAR transmittance in the wet state. For the photoselective cladding materials, the spectral dependency of the transmittance was only slightly changed by the condensate.     

Cold storage and laboratory incubation of intact soil cores do not reflect in-situ nitrogen cycling rates of tropical forest soils

Measurements of N transformation rates in tropical forest soils are commonly conducted in the laboratory from disturbed or intact soil cores. On four sites with Andisol soils under old-growth forests of Panama and Ecuador, we compared N transformation rates measured from laboratory incubation (at soil temperatures of the sites) of intact soil cores after a period of cold storage (at 5 °C) with measurements conducted in situ. Laboratory measurements from stored soil cores showed lower gross N mineralization and NH₄⁺ consumption rates and higher gross nitrification and NO₃⁻ immobilization rates than the in-situ measurements. We conclude that cold storage and laboratory incubation change the soils to such an extent that N cycling rates do not reflect field conditions. The only reliable way to measure N transformation rates of tropical forest soils is in-situ incubation and mineral N extraction in the field.     

豫北低山丘陵区农田边界系统植物多样性的研究

通过野外调查研究了豫北低山丘陵区不同农田边界的植物丰富度、均匀度、生态优势度和多样性指数。结果表明: 植物丰富度指数依次为灌草丛>水渠边>稀疏林地>路旁>果园边际>作物边界带, 灌草丛物种丰富度显著大于其他边界类型, 作物边界带的物种丰富度显著小于其他农田边界类型; 植物均匀度指数依次为稀疏林地>灌草丛=水渠边>路旁>作物边界带>果园边际, 稀疏林地均匀度指数显著大于其他边界类型, 果园边际地的均匀度指数显著小于其他农田边界类型; 植物多样性指数和生态优势度指数变化趋势一致, 依次为水渠边>稀疏林地>灌草丛>果园边际>路旁>作物边界带, 水渠边的生态优势度和多样性指数均显著大于其他边界类型, 作物边界带的生态优势度和多样性指数均显著小于其他边界类型。灌草丛、路旁、水渠边、稀疏林地和果园边际地相互间的共有植物种较多, 其物种相似系数均在0.7以上, 而作物边界带与其他边界类型间的共有植物种较少, 物种相似系数也较低, 均在0.7以下, 其中, 作物边界带和灌草丛相似系数最低, 为0.47。     

净辐射通量观测方法及观测精度的不确定性研究

净辐射通量观测方法和观测精度的不确定性已日益被人们所认识和了解,除了各种净辐射通量观测方法自身存在的一些问题外,还涉及太阳辐射表的标定方法（特别是长波辐射表的标定）、各种辐射表的技术指标及正确使用和维护等问题,通过在野外对国产全波段净辐射表（Netpyrradiometer下称净辐射表）和“四路法”（4-waycomponent system)2种常用的净辐射通量观测方法进行对比试验。结果表明,净辐射通量观测精度随时间和天气状况变化有不确定性,温度变化和辐射表防风罩透过光谱的不一致性是导致辐射表测量不确定性的主要原因。     

不同磷肥水平的小麦冠层多光谱特征研究

利用便携式冠层光谱仪对小麦进行连续观测获取光谱数据。本文分析了小麦在不同P肥施用水平及生育期变化情况下冠层的光谱响应特征,运用t-检验等统计方法获得了小麦冠层光谱对不同P肥水平的敏感波段,并由此找到判断P肥施用是否合理的关键生育期。结果表明小麦冠层光谱的近红外波段(810~1100nm)对P素的相应关系优于可见光波段,870nm等近红外波段为小麦P素敏感波段;从拔节期到孕穗期前后为其P素丰缺状况光谱诊断的关键生育期;归一化植被指数(NDVI)也可与小麦产量建立很好的回归方程。     

Hyper-spectral remote sensing to monitor vegetation stress

Background, aim, and scope  Vegetation stress diagnoses based on plant sampling and physiochemical analysis using traditional methods are commonly time-consuming, destructive and expensive. The measurement of field spectral reflectance is one basis of airborne or spaceborne remote sensing monitoring. Materials and methods  In this study, paddy plants were grown in the barrels evenly filled with 10.0 kg soil that was mixed respectively with 0, 2.5 × 207.2 and 5.0 × 207.2 mg Pb per 1,000 g soil. Rice canopy spectra were gathered by mobile hyper-spectral radiometer (ASD FieldSpec Pro FR, USA). Meanwhile, canopy leaves in the field-of-view (FOV) of spectroradiometer were collected and then prepared in the laboratory, (1) for chlorophyll measurement by Model 721 spectrophotometer, and (2) for Pb determination by atomic absorption spectrophotometer (SpectraAA-220FS). Results and discussion  Canopy spectral reflectance in the region of visible-to-near-infrared light (VNIR) increased, because ascended Pb concentration caused the decrease of canopy chlorophyll content. In the agro-ecosystem, however, heavy metal contamination is presented typically as mixture and their interactions strongly affect actually occurring effects. Normalized spectral absorption depth (D _n), and shifting distance (DS) of red edge position (REPs) revealed the differences in Pb concentration for canopy leaves, especially at the early tillering stage. Due to insufficient biomass of rice plants, the 30th day was not reliable enough for the selection of crucial growth stages. Some special sensitive bands might be omitted at the same time because of limited sample sets. Conclusions  Our initial experiments are still too few in the amounts of both metals and plants neither to build accurate prediction models nor to discuss the transformation from ground to air/spaceborne remote sensing. However, we are pleased to communicate that ground remote sensing measurements would provide reliable information for the estimation of Pb concentration in rice plants at the early tillering stage when proper features (such as DS and D _n) of reflectance spectra are applied. Recommendations and perspectives  Hyper-spectral remote sensing is a potential and promising technology for monitoring environmental stresses on agricultural vegetation. Further ground remote sensing experiments are necessary to evaluate the possibility of hyper-spectral reflectance spectroscopy in monitoring different kinds of metals’ stress on various plants.     

漓江上游山区水源林叶面积指数变化的遥感监测

为了定量评价漓江上游山区复杂地形水源林叶面积指数(LAI)的变化,对阔叶林、针叶林、竹林样地以TRAC仪器测定LAI,利用遥感数据计算归一化植被指数(NDVI)、比值植被指数(SR)、减化比值植被指数(RSR)、土壤调整植被指数(SAVI)、增强植被指数(EVI),并从DEM数据获取高程、坡度、坡向,提出并建立复杂地形最优多植被指数组合估算山区林地LAI的神经网络模型,利用模型对1989–2009年6景TM/ETM遥感图像估算LAI空间分布。结果表明,神经网络解决了LAI与多植被指数的非线性回归方程无法引入地形因素、且方程系数较多较难确定的问题,提高了LAI的估算精度。研究区成熟阔叶林减少代之以大片种植经济幼林,是导致林地LAI变化的原因。1989-2000年,LAI≥6.0的林地面积比例从78.8%逐年急剧下降到44.1%,LAI在1.0~6.0的林地面积比例从20.8%大幅上升到55.4%;2000-2009年,随着幼林的生长、竹林的速生,LAI≥6.0的林地面积比例逐渐上升恢复到74.5%,但仍未恢复到1989年的面积比例,相应LAI在1.0~6.0的林地面积比例逐渐下降到25.1%。研究成果为漓江上游水源林生态评估提供参考。     

Evaluation of measurement accuracy and comparison of two new and three traditional net radiometers

Net radiation (R_n) is the sum of the radiant energy at the Earth's surface and is a major component of the surface energy balance. However, R_n is difficult to measure accurately, and multiple instruments are available to measure it. Two new instruments (Hukseflux Thermal Sensors B.V., model NR01; Kipp & Zonen B.V., model CNR 2) have been released within the past two years. We compared these models, two less-expensive older models (Kipp & Zonen B.V., model NR-Lite; Radiation and Energy Balance Systems, Inc., model Q*7.1), and a more expensive older model (Kipp & Zonen B.V., model CNR 1) over a uniform turfgrass surface for 33 days in mid-summer. Three replicates of each radiometer were included in the study (except for the CNR 1). The instruments that independently measure the four components of R_n (models CNR 1 and NR01) were typically the most accurate. Incoming shortwave measurements from the four component instruments were compared to a reference pyranometer, and outgoing longwave measurements were compared to infrared measurements of surface temperature. The differences from the reference pyranometer and surface temperature measurements were typically 2% or less. There was a difference of approximately 5% in incoming longwave measurements between these two radiometer models. This is likely due to differences in calibration approaches, which are discussed. This emphasizes the need for standardization of longwave calibration methods and establishment of a world reference for longwave radiation. The instruments that do not separate shortwave and longwave radiation into component measurements (net all-wave radiometers, models NR-Lite and Q*7.1) were generally the least accurate, and had offsetting day and night differences that reduced daily total R_n differences relative to the reference. The CNR 2 measures net shortwave and net longwave, and is an intermediate between a four component instrument and a net all-wave instrument. The R_n measurement accuracy of the CNR 2 typically fell between that of the two groups. Differences among radiometers tended to be larger at night than during the day, indicating higher variability in longwave measurements. An inversion (flip) test in the field showed the NR-Lites and Q*7.1s had well matched detectors, however two of the three replicate CNR 2s had mismatch errors greater than 5%. This becomes important for measurements over non-vegetated surfaces. The data presented here should be helpful in selecting the most cost effective instrument for a given application.     

利用高光谱微分指数反演油茶炭疽病病情指数的研究

通过实地调查油茶炭疽病病情指数,并使用美国ASD公司生产的手持式野外光谱辐射仪测定相应的油茶冠层光谱反射率,然后将光谱数据进行一阶微分与滑动平均滤波相结合的预处理,经相关分析,选取与病情指数极显著相关的微分指数,采用单变量线性和非线性回归方法,选取部分样本建立油茶炭疽病病情指数的反演模型,并利用其余样本对模型进行精度检验。结果表明,随着病情指数的增大,油茶冠层光谱的一阶微分值在可见光区域的反射峰和吸收谷逐渐消失,红边斜率逐渐减小;病情指数与冠层光谱一阶微分值在480～513 nm、526～569 nm、583～607 nm和669～727 nm 4个波段达到极显著相关;以SDr′为自变量的对数模型反演病情指数的精度最高,其计算出的预测值与实测值之间的相关系数r和均方根误差分别为0.869和0.067,预测精度较高。该研究结果表明利用高光谱微分指数反演油茶炭疽病病情指数是可行的,并为油茶林的健康评价提供了新的方法。     

Saltation transport on a silt loam soil in northeast Spain

The Ebro River valley in Northeast Spain experiences regularly strong west-northwest winds that are locally known as cierzo . When the cierzo blows, wind erosion may potentially occur on unprotected agricultural lands. In this paper the first results of field measurements of soil characteristics and saltation transport in the Ebro River valley near Zaragoza are presented. An experiment was conducted on a silt loam soil in the summers of 1996 and 1997. Two plots of 135×180 m were both equipped with a meteorology tower, three saltiphones (acoustic sediment sensors) and ten sediment catchers. The plots were different with respect to tillage practices. One plot received mouldboard ploughing followed by a pass of a compacting roller (conventional tillage—CT), whereas the other plot only received chisel ploughing (reduced tillage—RT). Soil characterizations indicated that soil erodibility was significantly higher in the CT plots than in the RT plots. Consequently, no significant saltation transport was observed in the RT plots during both seasons. In the CT plot, four saltation events were recorded during the 1996 season and nine events during the 1997 season. Most events were preceded by rainfall during the previous one or two days, which reduced saltation transport significantly. It is concluded that the occurrence of wind erosion in the Ebro River valley depends on the timing and type of tillage, distribution of rainfall and soil-surface crusting. Copyright © 1999 John Wiley & Sons, Ltd.     

褐潮土的光谱特性及用土壤反射率估算有机质含量的研究

本文通过ASDFR便携式光谱仪对132个风干土壤样品的光谱反射率进行了实验室测定。根据土样光谱反射率变化,获得了褐潮土土壤剖面的不同诊断层反射光谱特征。结果表明,在400～1200nm范围之间,土壤有机质含量与土壤光谱反射率有较好的相关性。利用导数光谱方法建立了预测土壤有机质含量的方程,提出了预测北京地区褐潮土有机质光谱的最佳波段。在波长447nm处采用反射率和A值(反射率倒数的对数)所建立的预测方程的预测精度较高。采用反射率的一阶微分建立的预测方程的最佳波段在516nm处。而A值一阶微分光谱在615nm处相关性最好。作为一项参考指标用光谱分析法评价土壤中有机质含量,以期对精准农业中土壤养分或肥力的预测具有一定的指导作用。     

GPS/MET误差分析及其在降水预报中的应用

GPS/MET反演的大气可降水量产品具有近实时、全天候等优点,可为全国水土保持领域的组网监测提供更多的数据支持,GPS/MET的数据质量对降水预报分析尤为重要.本研究将GPS大气可降水量与探空、微波辐射计进行对比,分析GPS/MET的数据质量;同时,分析GPS大气可降水量与地面降水的关系,探索GPS/MET在邻近降水预报中的作用.结果显示:1)2015年GPS大气可降水量与探空、微波辐射计的演变趋势总体一致,波峰和波谷有很好的对应性,全年看整层大气水汽含量存在着明显的月际变化,随时间呈单峰曲线分布;因此GPS/MET能较好的反映大气中可降水量随时间的变化.2)虽然GPS/MET与微波辐射计、探空2种探测手段的平均偏差较大,但是离散程度不大,说明GPS/MET与其余2种探测方法之间存在稳定的系统误差.3)大气可降水量在地面降水发生前十几个小时开始增大,随后维持在一个高值的水平上,说明在降水前大气中有一个明显的水汽积累的过程.地面降水发生时大气可降水量达到最大值,降雨强度的极大值与可降水量的极大值有很好的对应.地面降水过程结束后,可降水量量迅速下降.4)大气可降水量的极大值是降水产生的必要条件.综合考虑降水次数和降水概率后,选取大气可降水量连续4h增加6 mm以上为判断降水发生的依据之一;因此,GPS/MET数据质量较可靠且在降水预报中具有指示性作用,作为气象和水土保持学科交叉的纽带,可为水土保持业务和决策部门决策分析和制定方面提供数据支撑.     

Denitrification and nitrous oxide to nitrous oxide plus dinitrogen ratios in the soil profile under three tillage systems

There is a growing interest in the adoption of conservation tillage systems [no-till (NT) and reduced tillage (RT)] as alternatives to conventional tillage (CT) systems. A 2-year study was conducted to investigate possible environmental consequences of three tillage systems on a 2.4-ha field located at Macdonald Research Farm, McGill University, Montreal. The soil was a sandy loam (0.5 m depth) underlain by a clay layer. Treatments consisted of a factorial combination of CT, RT, and NT with the presence or absence of crop residue. Soil NO₃^--N concentrations tended to be lower in RT than NT and CT tillage treatments. Denitrification and N₂O emissions were similar among tillage systems. Contrary to the popular assumption that denitrification is limited to the uppermost soil layer (0–0.15 m), large rates of N₂O production were measured in the subsurface (0.15–0.45 m) soil, suggesting that a significant portion of produced N₂O may be missed if only soil surface gas flux measurements are made. The N₂O mole fraction (N₂O:N₂O+N₂) was higher in the drier season of 1999 under CT than in 2000, with the ratio occasionally exceeding 1.0 in some soil layers. Dissolved organic C concentrations remained high in all soil depths sampled, but were not affected by tillage system.