Study on structure and function of an earthen bund irrigation system in Northeast Thailand

In Northeast Thailand, which overlaps with an erosional plain that is not suitable for irrigation because of poor water resources and terrains that prevent efficient water distribution, farmers have long supplied water to surrounding paddy fields by blocking rivers completely with earthen bunds. Although such a traditional irrigation system fits well with the characteristics of Northeast Thailand, those who are concerned with modern irrigation development projects in Northeast Thailand seem to have been paying little attention to it. The present study was performed to facilitate development of more appropriate irrigation systems in Northeast Thailand by providing information regarding traditional irrigation methods. We investigated the traditional irrigation methods with earthen bunds at three study sites, and our results indicated that styles of irrigation vary with riverbed slope. The traditional irrigation system that is used in most of Northeast Thailand is different from ordinal weir irrigation, in that paddy fields are not irrigated by gravity flow but by backwater of earthen bunds. Our results suggest that the development of more successful irrigation systems would be possible through improvement of the design ideas of traditional irrigation methods.

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。     

祁连山中段草地土壤有机碳分布特征及其影响因素

本文通过调查祁连山中段草地3个海拔段共9条样带,研究了土壤有机碳随海拔、坡向、坡位的分布特征及环境影响因素。结果表明,祁连山中段草地0~60 cm土壤有机碳密度变化范围为9.98~38.96 kg·m^-2,均值为22.31 kg·m^-2。不同海拔间,3 350 m土壤有机碳密度最大,分别是2 900 m和2 450 m处的2.07和3.41倍;在山坡区域,西坡土壤有机碳密度高于南坡和西南坡;沟谷显著高于坡顶和山坡的上、中、下坡位。回归分析表明,土壤有机碳密度与土壤含水量的关系最密切,回归方程的复相关系数（R²）达0.85。一般线性模型表明,地形对0~60 cm土壤有机碳密度空间变异的解释率高达90.68%,其中海拔和坡位分别贡献了71.82%和15.78%。因此,在构建该区草地土壤有机碳储量估算模型时,应重点考虑海拔和坡位因子的指示性。     

地形和土壤属性对大豆产量的影响

正确理解作物产量的变异性特征及其影响因素是对农田地块进行科学管理的基础。地块的地形特征是导致作物产量变异形成的主要因素。本文选择代表不同地形特征的洼地农田和岗地农田为研究对象,分析地形对土壤属性和大豆产量的影响以及它们之间的相互关系。研究结果显示,洼地农田与岗地农田的土壤属性和大豆产量均存在显著性差异(P<0.05)。洼地农田的土壤养分含量较高,但土壤结构较差,其平均重量直径(MWD)和几何平均直径(GMD)显著小于岗地农田,质量分形维数(Dm)显著大于岗地农田;在两类农田地块中,大豆产量的差别较大,洼地农田的大豆产量仅为岗地农田的62%。相关性分析表明,大豆产量与土壤结构稳定性和地块高程呈极显著正相关(P<0.01);土壤有机碳和土壤养分对大豆产量没有显著影响。     

浅谈应用地理信息系统绘制地形林相图

文章以地理信息系统软件ArcGIS、森林资源监测与管理GIS系统软件、EzMap为平台,介绍绘制地形林相图的方法和技巧。     

不同地形对年橘留树保鲜果实品质的影响

为了探讨地形对龙门年橘留树保鲜过程中果实品质的影响,进行了连续3 a的观测,结果表明地形对年橘留树保鲜果实外观内质均有影响,坡地年橘果实的维生素C含量、可溶性固形物含量、还原糖、蔗糖和总糖含量均高于平地果园,其峰值在2月中旬左右和平地果园同时或稍晚出现,此后含量都出现下降,不同物质的下降速度不同,但不同地形对同种物质下...     

Prehispanic changes in wetland topography and their implications to past and future wetland agriculture at Laguna Mandinga,Veracruz, Mexico

We report core stratigraphy and chronology that explains the diachronic history of the surface in a prehispanic wetland agricultural complex of planting platforms and canals at Mandinga, central Veracruz, Mexico. Using recognizable stratigraphic horizons, elevations of prehistoric surfaces were measured for the wetland prior to the construction of platforms and canals, immediately following construction, at the time of abandonment, and of the present-day surface. Significant topographic and hydrological changes are evident. We discuss our results in the light of prehispanic water management and cultivation and postulate water storage within the wetland, a patchy management of water and cultivation, and variable productivity. The paper ends with a discussion of the lessons that can be learned when contemplating contemporary cultivation of wetlands. In addition to the environmental concerns, we emphasize the need to consider the physical, socio-economic, and political contexts in which contemporary wetland agriculture would have to operate.     

Role of landscape and hydrologic attributes in developing and interpreting yield clusters

Management of agricultural fields based on yield patterns may help farmers adopt environmentally friendly farming practices. Our objective was to investigate landscape and hydrologic attributes that affect spatial clusters of corn (Zea mays L.)-soybean (Glycine max L.) yields. The study was conducted at Iowa State University's northeastern research center near Nashua, Iowa, from 1993 to 1998. The yield data, normalized for annual climatic variability, were used in cluster and discriminant analysis, and the landscape and hydrologic data were overlain using ArcGIS software. Three clusters of low, medium and high categories were formed using 10 iterations with zero convergence options and satisfying the R², pseudo F-statistic and cubic clustering criteria. The spatial clusters, however, varied greatly over space and time domain for the study period. The map overlay analysis using ArcGIS showed that high yield clusters were affected by soil and lower elevation levels in the below average precipitation year of 1994. The annual normalized subsurface drainage volume, nitrate leaching losses, soil type and topographic attributes of slope, aspect, and curvature were used in stepwise discriminant analysis to identify the variables significantly related to the clusters. Soil and topographic attributes of curvature and aspect contributed significantly in cluster formations for four of the six years at P ≤ 0.15. The results suggest that cluster and discriminant analysis can be useful for identification of soil and topographic attributes affecting corn and soybean yield patterns, which can help in delineation of management zones for site specific management practices.     

Pre-EuroAmerican settlement forests in Redwood National Park,California, USA: a reconstruction using line summaries in historic land surveys

Extensive logging in the twentieth century destroyed much of the coniferous forests in the lower Redwood Creek basin of Redwood National Park. Restoration of cutover lands requires the identification of historical, pre-logging reference conditions. Field notes from the original Public Land Surveys were used to reconstruct the pre-EuroAmerican settlement forests. Most reconstructive studies based on historic surveys rely on bearing tree evidence over large areas to determine vegetation patterns over several hundreds to thousands of square kilometers. Due to the small size of the study area (approximately 200 km²), bearing tree evidence could not accurately reconstruct the vegetation at this scale. Instead, lists of the overstory and understory vegetation for each surveyed mile (line summaries) were employed. Analysis of line summaries evidence identified the historical importance, geographical range, and environmental influences on woody species and vegetation communities. Topography, especially elevation, and soil texture were significantly correlated with plot-scale ordination scores derived from non-metric multidimensional scaling. The influence of topography and distance to ocean coast on the historical distribution of dominant woody species concurs with findings from present-day field studies of local and regional old-growth forest. A comparison with present-day vegetation maps revealed that coast redwood (Sequoia sempervirens), Douglas fir (Pseudotsuga menziesii), Sitka spruce (Picea sitchensis), and red alder (Alnus rubra) experienced the most substantive changes in the vegetation as a result of twentieth century land use activities.     

<Emphasis Type="Italic">β</Emphasis>-Diversity and vegetation structure as influenced by slope aspect and altitude in a seasonally dry tropical landscape

Topography strongly affects the distribution of insolation in the terrain. Patterns of incoming solar radiation affect energy and water balances within a landscape, resulting in changes in vegetation attributes. Unlike other regions, in seasonally dry tropical forest areas the potential contribution of topography-related environmental heterogeneity to β-diversity is unclear. In Mt. Cerro Verde (Oaxaca), S. Mexico, we: (1) modelled potential energy income for N- and S-facing slopes based on a digital elevation model, (2) examined the response of vegetation structure to slope aspect and altitude and (3) related variations in plant diversity to topography-related heterogeneity. Vegetation survey and modelling of potential energy income (SOLEI-32 model) were based on 30 plots equally distributed among three altitudinal belts defined for each slope of the mountain; combining the three altitudinal belts and the two slopes produced six environmental groups, represented by five vegetation plots each. Potential energy income was about 20% larger on the S than on the N slope (9,735 versus 8,138 MJ/m²), but it did not vary with altitude. In addition, the temporal behaviour of potential energy income throughout the year differed greatly between slopes. Vegetation structure did not show significant changes linked to the environmental gradients analysed, but altitude and aspect did affect β-diversity. We argue that the classic model of slope aspect effect on vegetation needs reconsideration for tropical landscapes. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorised users.