柑橘生长与生态因子的关系研究进展

根据柑橘生长与生态因子关系的近期研究成果,本文阐述了柑橘生长与光照、温度、降水、土壤有机质、土壤营养元素、土壤酸碱度、土壤水分、土壤质地及结构、土层厚度、土壤微生物以及地形等生态因子间的关系。由此得出,柑橘类果树的个体发育和系统发育是自身遗传背景与外部生态因子相互作用、相互适应的结果。     

2019年3月岳阳一次强对流天气过程的成因分析

整理分析岳阳2019年3月20—21日常规天气观测资料、NECP再分析数据,结合多普勒天气雷达资料及产品,应用天气学、雷达气象学方法对此次强对流天气过程的背景及环境场条件进行分析。结果表明,前期不稳定能量积聚,19—20日地面倒槽发展,南风强盛,岳阳市前期地面升温明显,最高气温达到28℃以上;500 hPa中高纬为多波动型,湖南处于槽前西南气流控制下,850 hPa四川、贵州交界处有低涡形成,中低层切变移动影响岳阳,为此次强对流过程提供了动力条件;地面冷空气南下,斜压锋生,触发对流发展;中低空西南急流建立,来自孟加拉湾的强盛的水汽输送与持续的水汽辐合,为此次强对流过程提供了充沛的水汽供应和动量输送,同时也大大加强了低层上升运动的形成,为降水的发生发展提供了动力与热力条件;此外,垂直上升运动的大值区与强对流发生时段对应较好,K指数、沙氏指数及对流不稳定能量CAPE已达到岳阳出现强对流和短时暴雨指标;在强对流预报中,不仅要考虑大尺度环流及特征物理量,也要考虑地形对降水及强对流天气的影响。     

青海海南州地理与气象对强对流天气的影响

通过"711"数字化雷达观测,对128个对流单体、复合体资料进行了分析研究。得出青海海南州地区发生强对流天气系统的发源地及影响海南地区强对流天气发生和发展的天气形势,对灾害性对流天气临近预报有较好的指导意义。     

Field calibration of an impedance soil water probe for the shallow seedbed across field topography

Impedance soil water probes enable frequent and non‐destructive determination of soil water status in situations where gravimetric soil sampling is too demanding of time and sampling space. The ThetaProbe is an impedance soil water probe requiring calibration for local soil conditions, because measurement accuracy can be affected by properties of the soil. Often, only a single calibration is performed for an experimental site. An experiment investigating the seedbed to 75‐mm depth across a field topography with variable soil properties was examined to determine which soil properties affected the calibration of the ThetaProbe, and if soil‐specific calibration was required to derive suitable estimates of the water status in the experiment. Experimental factors examined included hillslope aspect, hillslope position, crop residue and soil depth. Soil properties, other than volumetric water content, significantly affecting the probe measurements were bulk density, electrical conductivity and temperature. The probe underestimated soil water at very low water contents, and overestimated soil water at contents greater than 11 m³ m^?3, compared with gravimetric measurements. A single calibration, not corrected for hillslope position at a water content of 20 m³ m^?3, overestimated water content by 0.02 m³ m^?3 in the summit hillslope position and underestimated water content by 0.04 m³ m^?3 in the toeslope position. A single calibration, not corrected for soil depth at a water content of 20 m³ m^?3, overestimated water content by 0.02 m³ m^?3 in the 0‐ to 25‐mm soil layer and underestimated water content by 0.03 m³ m^?3 in the 50‐ to 75‐mm layer. The complexity of microsites in a shallow seedbed requires soil‐specific calibration in field experiments containing heterogeneous soil properties.     

Physical influences of landscape on a large-extent ecological disturbance: the northeastern North American ice storm of 1998

The 1998 ice storm was a large-extent ecological disturbance that severely affected the eastern Adirondack forests of northern New York. Ice damage produced widespread breakage of limbs and trunks in susceptible trees. Although ice storms are common within northeastern North American forests, the magnitude and extent of the 1998 storm far exceeded damage caused by typical ice storms in the recent past. While plot and stand-scale ecological impacts of ice storms have received attention insofar as tree species vulnerability, stand age susceptibility, and microhabitat alterations, larger-extent damage patterns have not been previously evaluated. The normalized difference vegetation index (NDVI) was employed to assess forest vigor and canopy density in atmospherically corrected Landsat Thematic Mapper (TM) satellite imagery of the Adirondacks. Digital change analysis of the baseline forest condition (1990 NDVI data), and the condition encountered in a post-storm image (1998 NDVI data) was conducted. Forest damage was separated from natural variations in canopy reflectance by employing a generalized linear model that incorporated in situ measurements. A robust empirical variogram analysis revealed that locations of tree damage were significantly correlated for distances up to 300 meters. Intensely-damaged forest exhibited greater spatial dependence, but over a smaller distance. Canopy damage was not greater proximate to stream and forest boundaries, and did not follow our hypothesis of decreasing damage with distance from the boundary. Overall, we show that local topography (elevation and aspect), forest composition (deciduous or coniferous), and the meteorological characteristics of the disturbance event acted together to determine the spatial extent of ice storm damage.This revised version was published online in May 2005 with corrections to the Cover Date.     

Algorithms for sensor-based redistribution of nitrogen fertilizer in winter wheat

Several methods were developed for the redistribution of nitrogen (N) fertilizer within fields with winter wheat (Triticum aestivum L.) based on plant and soil sensors, and topographical information. The methods were based on data from nine field experiments in nine different fields for a 3-year period. Each field was divided into 80 or more subplots fertilized with 60, 120, 180 or 240 kg N ha⁻¹. The relationships between plot yield, N application rate, sensor measurements and the interaction between N application and sensor measurements were investigated. Based on the established relations, several sensor-based methods for within-field redistribution of N were developed. It was shown that plant sensors predicted yield at harvest better than soil sensors and topographical indices. The methods based on plant sensors showed that N fertilizer should be moved from areas with low and high sensor measurements to areas with medium values. The theoretical increase in yield and N uptake, and the reduced variation in grain protein content resulting from the application of the above methods were estimated. However, the estimated increases in crop yield, N-uptake and reduced variation in grain protein content were small.     

Soil carbon mapping using on-the-go near infrared spectroscopy, topography and aerial photographs

Efficient tools for accurate soil carbon (SC) mapping are imperative for large scale assessment of total SC stocks and their changes in time as well as for site-specific tailoring of agricultural management practices. On-the-go near infrared (NIR) reflectance spectroscopy has been used recently in aid to the conventional, laborious and expensive soil analyses, since NIR measurements are taken in-situ quickly and non-destructively. However, NIR spectrum data need to be effectively calibrated with conventionally measured SC. Our objectives are to compare calibration approaches, including pre-processing transformations (Savitzky-Golay derivatives, standard normal variate and mean centering) and multivariate statistical methods (principal component regression, partial least squares, partial least squares leaving one-outlier-out) for using NIR spectra data as SC predictor, to evaluate NIR reliability in predicting SC under low carbon contents typical for Midwest Alfisols; and finally to compare predictions of SC by using three sources of auxiliary information (NIR spectral data, visible-NIR reflectance obtained from aerial photographs and topographical features). No improvements in calibration accuracy were observed when using pre-processing transformations. Partial least squares (RMSE = 1.90) tended to perform better than principal component regression (RMSE = 1.96); especially when spectral-NIR outliers are dropped (RMSE = 1.68). Our results suggested that visible-NIR data from aerial photographs used along with topographical attributes outperformed on-the-go spectral NIR data. Topographical data improved prediction in the models with aerial photograph visible-NIR data; however no improvement was noticed when used with spectral-NIR data. Though, NIR spectral data is frequently used as a proxy for SC prediction, we notice that this auxiliary information is not well suited under all scenarios. Particularly, when SC levels are low and the range of SC data is narrow, as in this study, NIR was only moderately successful in predicting SC.     

Landscape-scale estimates of dinitrogen fixation by Pisum sativum by nitrogen-15 natural abundance and enriched isotope dilution

Topography and slope position influence the soil and environmental factors that affect N₂ fixation by legumes. The present study was conducted to (1) estimate N₂ fixation by field peas in a gently rolling farm field using the natural ¹⁵N abundance and the ¹⁵N-enriched isotope dilution techniques and (2) identify soil and environmental factors that influence N₂ fixation at the landscape scale. Whereas soil available water capacity, available NH _inf4 ^sup+ , total crop yield, and percent N derived from N₂ fixation (% Ndfa) estimated using enriched N were significantly affected by landform patterns, soil NO _inf3 ^sup- levels, seed yield, and the % Ndfa estimated using natural abundance did not follow landform patterns. The % Ndfa using natural abundance was correlated with NH _inf4 ^sup+ but not with available soil water, pH, electrical conductivity, NO _inf3 ^sup- , or particle size. Estimates of the % Ndfa using enriched ¹⁵N ranged from 0 to 92.8%. The highest median value (68.6%) for % Ndfa using enriched N occurred on the divergent footslopes, with the lowest value (28.1%) on the convergent shoulders. Estimates of % Ndfa using natural abundance ranged from 13.2% to 96.9%. Smaller fluctuations during the growing season in the ¹⁵N of the available N pool may have resulted in less variability for % Ndfa using natural abundance compared to enriched ¹⁵N. Despite similar mean values for % Ndfa using natural abundance (44.5) and enriched ¹⁵N (49.6), no significant correlation between the two estimates was found. These results suggest that although topography may exert gross controls on N₂ fixation, large variations in N₂ fixation at the microsite level may preclude correlations between individual estimates and limit detection of landscape scale patterns of N₂ fixation.Contribution No. R754 of the Saskatchewan Center of Soil Research     

Topographic and compositional influences on disturbance patterns in a northern Maine old-growth landscape

Disturbance patterns are strongly coupled with forest composition and structure, and patterns change through time in response to shifts in climate, anthropogenic impacts and other factors. Knowledge of the natural disturbance patterns for establishing baseline conditions for a forest type or ecosystem facilitates change detection for other elements of the biophysical system important to management and conservation. Dendrochronological reconstructions from old-growth forest remnants throughout northeastern North America document average decadal rates of disturbance of 5%–<10% over the last 150–300 years. Relatively frequent, low severity disturbance characterized by small gaps representing canopy openings made by 1–3 trees prevail in these forests dominated by varying mixtures of late-successional tree species. Few studies, though, have explicitly characterized differences related to composition or topographic setting in old-growth landscapes. We addressed this by comparing the temporal and spatial disturbance patterns reconstructed from tree rings at two spatial resolutions (0.5 ha and 200 m²). Sites were selected to assess the influence of topography (slope) and cover type in stands where red spruce (Picea rubens Sarg) and balsam fir (Abies balsamea L. Mill) were key components. Low rates of disturbance (average <10% per decade) and small gap sizes (≤30 m²) prevailed in all stands during the decades from 1850–1980. Episodic pulses of disturbance, of nearly moderate intensity in some stands, opened ca. 20–30% of the canopy area and were associated with wind events and/or insect outbreaks that differentially affected stands. We found no significant difference in the average temporal rates of disturbance related to cover type or topography in 0.5-ha plots. However, the influence of these factors was evident in comparisons of gap areas estimated for 200-m² plot sections. At this resolution, the largest canopy openings (≥100 m²) occurred most frequently in slope sites, enabling pulses of canopy accession for Betula alleghaniensis (Britton). Whereas the smallest canopy openings (≤30 m²) dominated softwood stands, favoring red spruce, balsam fir and other shade-tolerant species throughout the forest. The variable effects of common disturbance agents, regardless of topographic position and/or cover types, points to the important role of biological legacies determining stand structure and composition on subsequent disturbance events and long-term patterns.     

生物炭对山坡地烟叶产量和氮肥利用效率的影响效果评价

山坡地土壤有机质含量低和保水保肥能力差是导致烤烟产量普遍低于山间平地的重要原因之一。生物炭可以改善土壤物理化学性质,提升土壤保水保肥能力,本试验研究其对烤烟产量和氮肥利用效率的影响。通过二因素两种地形（山坡地、山间平地）和6个生物炭施用量处理（0、4.5、9.0、13.5、18.0、22.5t/hm ²）的大田试验,评价生物炭对烟叶产量和产值、烟株农艺性状、氮肥利用效率和氮素表观损失量的影响。结果表明,山坡地烤烟产量和产值显著低于山间平地。同一生物炭施用量条件下,山坡地烟叶产量和产值相对增幅显著高于山间平地。当生物炭施用量介于0~13.5t/hm ²时,山坡地烟叶产量和产值均随生物炭施用量增加而显著增加;而进一步提高生物炭施用量,烟叶产量和产值增加不显著。山间平地烟株氮素吸收量、氮肥农学利用率和氮肥回收利用率均显著高于山坡地烟株。与不施生物炭的对照相比,山坡地烟株氮肥农学利用率和氮肥回收利用率相对增幅均显著高于山间平地烟株。随着生物炭施用量增加,氮素表观损失量显著降低。相对于山间平地而言,山坡地植烟区应用生物炭的增产增收和提高氮肥利用效率的效果更加显著,其适宜生物炭施用量为13.5t/hm ²。