A riverscape perspective on habitat associations among riverine bird assemblages in the Lake Champlain Basin,USA

The riverscape perspective recognizes the heterogeneous habitat types within the stream corridor as a single, integrated ecological unit operating across spatial scales. Although there is ample evidence that the riverscape notion is appropriate in understanding the physical phenomena of stream corridors, significantly less attention has focused on its ecological ramifications. To this end, we surveyed riverscape habitat variables and bird community characteristics in the Champlain Valley of Vermont, USA. From the data collected, we used information theoretic methodology (AIC_c) to model relationships between bird community attributes and key habitat variables across the riverscape. Our models with the greatest support suggest that riverine bird communities respond to a suite of characteristics; representing a variety of riverscape habitats at the in-stream, floodplain, and riparian levels. Channel slope, drainage area, percent conifers, and in-stream habitat condition were among the most influential variables. We found that piscivores are potentially important indicators of riverscape condition, responding to a host of variables across the riverscape. Our results endorse a holistic approach to assessing and managing the mosaic of patches in the riverscape and suggest that a riverscape approach has significant conservation potential.     

Development of a spot plow providing complete inversion for effective weed control

Tillage for the "complete inversion" of soil, that is, overturning soil slices 180° was proposed, a "spot plow" was developed and tested to accomplish the task, and a simulation model was evaluated to demonstrate the efficacy of the plow on weed control. A 360 mm wide spot plow was designed to operate at a speed of 1.9 m s⁻¹ for the spot plowing with the least possible lateral displacement of the soil slice by utilizing the inertia of the soil slice and securely rotating it. In field experiments, complete spot inversion required an operating speed of at least 1.6 m s⁻¹; at lower speeds, a portion of the soil block was left half-inverted and further lowering led to considerable lateral displacement. The displacement in the forward and lateral directions was minimal, implying that spot plowing is suitable for potential application to and verification of the weed population dynamics model in the field. A simple linear matrix model of the population dynamics of annual weeds was proposed, whereby four layers of soil were set to describe tillage and other ecological events. The effect of tillage on weed control was evaluated by the equilibrium reproduction rate allowed to sustain a stable population of weeds. The simulation model showed that alternately changing the depth of spot plowing had a significant effect on controlling weeds of low-survival-rate seeds, even when some incomplete inversion of the soil slice was taken into account.     

人类活动对晋西北地区生态环境影响的初步研究

晋西北地处我国北方生态环境脆弱的农牧交错带,同时又是资源富集,资源与环境的矛盾十分突出。人类不合理的经济活动加剧了该区以土壤风蚀沙化和水土流失为主的环境退化问题。因此,加强环境保护刻不容缓。     

规模种植条件下玉米茬地平翻整地机组经济性评价

玉米后茬耕整地是玉米机械化生产过程中的重要环节之一,评价玉米茬地机械化耕整地机组的经济性能对指导农业及农业机械化生产具有重要意义。根据实际调研结果,确定了规模化生产条件下玉米茬地平翻整地工艺过程及完成各项作业的10种适用机组;选择年最大盈利值、投资回收期和内部收益率评价玉米茬地平翻整地各机组的经济性能,给出了各指标的计算模型。评价结果表明:东方红1304拖拉机灭茬机组、CASE210拖拉机耙地机组年收益最大;东方红1304拖拉机起垄机组、CASE210拖拉机平翻机组可获得较高的投资效率。     

稻油轮作区驱动圆盘犁对置组合式耕整机设计与试验

针对长江中下游稻油轮作区油菜种植时土壤黏重板结、秸秆量大、播种作业需同步开畦沟的农艺要求,考虑传统耕整作业耕层浅、功耗大的不足,依据驱动圆盘犁组与传统铧式犁相比,不易缠草堵塞、通过性好、牵引阻力小的特征,设计了用于油菜播种的驱动圆盘犁对置组合式耕整机。提出了主动式对置犁耕与被动式开畦沟、碎土、平整相结合的联合耕整作业方案,分析了对称布置的圆盘犁组的动力学和运动学特性,确定了其主要结构和工作参数。根据犁体曲面成形原理,设计了开畦沟前犁犁体曲面;依据组合式船型开沟器与土壤挤压互作机制的分析,确定了开畦沟区域宽度为350 mm时,开畦沟系统作业后可有效保证畦沟和种床厢面质量。耕深稳定性试验表明,整机作业实际耕深与限深深度基本一致,耕深稳定性系数均在90%以上。厢面质量试验表明,开畦沟系统在中间开畦沟区域能开出沟宽241.6~293.5 mm,沟深328.6~370.8 mm的梯形沟。经组合式船型开沟器挤压的土壤对犁沟的实际填埋率高于87.67%,碎土辊作业后厢面平整度为22.45~26.70 mm,碎土率为60.14%~68.37%。正交试验结果表明,整机较优工作参数为:限深深度为180 mm,机组前进速度为3.5 km/h,圆盘犁组转速为160 r/min,此时整机功耗为24.37 k W,相比传统旋耕方式的油菜播种种床整备机具的功耗降低了37.67%,秸秆埋覆率为92.78%,碎土率为66.74%,厢面平整度为24.18 mm,土壤对犁沟平均填埋率为92.3%,满足油菜播种的农艺要求。     

Application of the Soil and Water Assessment Tool (SWAT) to predict the impact of alternative management practices on water quality and quantity

Alternative land management practices such as conservation or no-tillage, contour farming, terraces, and buffer strips are increasingly used to reduce nonpoint source and water pollution resulting from agricultural activities. Models are useful tools to investigate effects of such management practice alternatives on the watershed level. However, there is a lack of knowledge about the sensitivity of such models to parameters used to represent these conservation practices. Knowledge about the sensitivity to these parameters would help models better simulate the effects of land management. Hence, this paper presents in the first step a sensitivity analysis for conservation management parameters (specifically tillage depth, mechanical soil mixing efficiency, biological soil mixing efficiency, curve number, Manning's roughness coefficient for overland flow, USLE support practice factor, and filter strip width) in the Soil and Water Assessment Tool (SWAT). With this analysis we aimed to improve model parameterisation and calibration efficiency. In contrast to less sensitive parameters such as tillage depth and mixing efficiency we parameterised sensitive parameters such as curve number values in detail.In the second step the analysis consisted of varying management practices (conventional tillage, conservation tillage, and no-tillage) for different crops (spring barley, winter barley, and sugar beet) and varying operation dates. Results showed that the model is very sensitive to applied crop rotations and in some cases even to small variations of management practices. But the different settings do not have the same sensitivity. Duration of vegetation period and soil cover over time was most sensitive followed by soil cover characteristics of applied crops.     

Effect of Tillage and Plant Residue Management Practices on Shrinkage of a Vertisol

A study was carried out to determine the effects of different tillage and plant residue management practices on different soil moisture and shrink-swell properties of a Vertisol (very fine, semctitic, thermic, chromic Haploxerert (with less than 1 % slope). The core samples were collected in July (after harvesting of lentil) and in November (after planting of wheat) 1993. The two tillage methods were moldboard (T1) and chisel (T2). The two plant residue incorporation dates were in August (R1) and in October (R2). Results indicated that T2 tends to give higher water holding capacity and available moisture than T1. Immediate incorporation of plant residue (R1) tends to increase the bulk density and to decrease soil specific volume and void ratio when compared to late incorporation treatment (R2). In general, the two tillage treatments tend to decrease moisture availability, shrinkage characteristics, soil specific volume, and void ratio. They also tend to increase the soil shrinkage (subsidence and cracks volume) and bulk density. Chisel plough is recommended in Vertisols, if it is to be used before the rainfall.     

Effect of Tillage System on Soil Strength and Bulk Density of Vertisols

Improving the soil environment for seedling emergence and plant growth is possible using a good tillage system. From March 1993 until June 1994, the effect of tillage system and plant residue incorporation practices on the bulk density and the soil strength of the surface layer of a vertisol (very fine, smectitic, thermic, chromic Haploxerert), on a less than 1 % slope, was investigated. The two tillage methods were moldboard (T1) and chisel (T2). The two plant residue incorporation dates were in August (R1) and in October (R2). Results indicated that R1 gave significantly higher bulk density than R2, while the different tillage treatments had no significant effect. Soil strength was significantly lower under T1 and R2 than under the other treatments.     

Weed control in conservation agriculture systems of Zimbabwe: Identifying economical best strategies

Weed management under conservation agriculture (CA), especially when manually controlled is one of the major setbacks for the widespread adoption of CA in southern Africa. This study was conducted at three on-station and three on-farm sites: CIMMYT-Harare, Domboshawa Training Centre and Henderson Research Station (on-station sites), Hereford farm, Madziva communal area and Shamva communal area (on-farm sites). The evaluation focused on the effect of initial herbicide application and succeeding manual weeding whenever weeds were 10 cm tall or 10 cm in length for grasses with stoloniferous–rhizomatous growth habit. Weeds counts, weeding time and grain yields were collected at all on-station sites. At the on-farm sites, weed counts were done before weeding and a number of farmers were timed during weeding. The results showed that herbicides use reduced the weed density and time taken on weeding at all sites. Combining herbicides e.g. atrazine, glyphosate and metalachlor had the lowest weed density and weeding time at all sites. However, the treatments had no effect on maize grain yields suggesting that appropriate and timely manual weeding reduced crop/weed competition. Herbicides treatments had higher input costs than manual weeding due to the additional cost of herbicide but the treatment with manual weeding only had more overall labour days compared to the mixture of three herbicides. In order to achieve economic benefits, smallholder farmers may use the time for value addition e.g. expand cropped land area, use time for value addition, or sell new products on the market. Herbicides use reduces the manual labour needed to control weeds and minimise total crop failure due to untimely weeding hence, herbicides are an important but not the only weed control option under CA systems in Zimbabwe.     

玉米根茬图像的分割方法

对保护性耕作留茬覆盖情况下田间玉米根茬图像进行了分割.选取采集图像的彩度信息作为对象,通过对几种常用的自动阈值选取算法的比较,选择了迭代法对田间图像进行分割.实验结果表明:该方法能够有效地将根茬目标与土壤背景分割开来,为下一步检测行茬直线并将其作为导航基准线进行视觉导航的研究提供了基础.