免耕稻田田面水磷素动态及其淋溶损失

以免耕和翻耕稻田为研究对象,通过大田试验与室内分析,研究了不同耕作方式下稻田田面水和渗漏水的淋溶损失及其对环境的影响。试验共设4个处理,分别是免耕+不施肥(NT0)、翻耕+不施肥(CT0)、免耕+复合肥(NTC)和翻耕+复合肥(CTC)。结果表明,施磷肥显著提高稻田田面水以及渗漏水各形态磷浓度。施磷肥2d后田面水总磷(TP)浓度、颗粒态磷(PP)浓度和溶解磷(DP)浓度即达到最大值,此后由于水中颗粒或表土对田面水磷素的固定,磷素的淋失,水稻生长吸收及前期的稻田排水和灌水稀释,1周后迅速降低并趋于稳定;渗漏水TP浓度和溶解磷(RP)浓度在施磷肥2d后达到最大值,渗漏水TP浓度在施肥后一个半月达到最低值,而渗漏水RP浓度在施肥4d后就降低到最低值。处理NTC田面水TP、DP与PP显著高于处理CTC,而处理NT0与处理CT0之间无差异;与翻耕相比,免耕不影响渗漏水TP与RP浓度及磷下渗淋失。对田面水磷素及渗漏水磷素变化动态分析表明,施磷肥后的1周左右是控制磷素流失的关键时期。     

风沙土条件下滴灌灌水定额与深层渗漏量关系研究

保水、保肥性极差的风沙土广泛分布于和田地区,为探明滴灌条件下其灌水定额与深层渗漏量的关系以及确定适宜灌水定额,为和田地区设施农业的科学灌溉提供理论依据.以和田风沙土条件下日光温室萝卜地为研究对象,设置了5个灌水水平,开展定周期、变定额的灌溉试验,同时利用深层渗漏仪监测地面60 cm深度以下的深层渗漏量,分析了深层渗漏量...     

Transitions in forest fragmentation: implications for restoration opportunities at regional scales

Where the potential natural vegetation is continuous forest (e.g., eastern US), a region can be divided into smaller units (e.g., counties, watersheds), and a graph of the proportion of forest in the largest patch versus the proportion in anthropogenic cover can be used as an index of forest fragmentation. If forests are not fragmented beyond that converted to anthropogenic cover, there would be only one patch in the unit and its proportional size would equal 1 minus the percentage of anthropogenic cover. For a set of 130 watersheds in the mid-Atlantic region, there was a transition in forest fragmentation between 15 and 20% anthropogenic cover. The potential for mitigating fragmentation by connecting two or more disjunct forest patches was low when percent anthropogenic cover was low, highest at moderate proportions of anthropogenic cover, and again low as the proportion of anthropogenic cover increased toward 100%. This fragmentation index could be used to prioritize locations for restoration by targeting watersheds where there would be the greatest increase in the size of the largest forest patch.     

Landscape patterns simulation with a modified random clusters method

A new modified random clusters method for the simulation of landscape the matic spatial patterns is presented. It produces more realistic and general results than landscape models that have been commonly used to date in the field of landscape ecology. Simulated patterns are said to be realistic, apart from their patchy and irregular appearance, because the values of the spatial indices as a function of habitat abundance measured in real landscape patterns (number of patches, edge length and patch cohesion index) can be replicated with the proposed landscape model. It allows a wide range of spatial patterns to be obtained, in which fragmentation and habitat abundance can be systematically and independently varied. Furthermore, a degree of control over the irregularity of the shapes of the simulated landscapes can be achieved, and it is also possible to simulate patterns with anisotropy. The proposed method is easy to implement and requires little computation time, which enhances the practical possibilities of this method in different areas of landscape ecology.     

Resource utilization scales and landscape pattern

The spatial patterning of resources constrains the movement of consumers on the landscape. Percolation theory predicts that an organism can move freely if its critical resource or habitat occupies 59.28% of the landscape. Sparse resources require an organism to operate on larger resource utilization scales. Multiple critical resources necessitate larger scales, while substitutable resources ease the scale requirements. Contagious spatial patterns require larger scales to permit movement between resource clusters. The study indicates a strong link between spatial pattern and ecological processes on a landscape.     

土壤水下渗解析解与数值解的比较研究

针对饱和—非饱和条件下土壤水的垂向下渗,分别用半经验计算公式和全物理基础的HYDRUS模型模拟了不同降雨情景下的土壤水渗漏量,对两种方法的计算结果进行了比较。结果表明,两种方法均能反映出土壤水渗漏率与降雨强度的相关性,降雨强度和降雨总量的增加引起土壤水渗漏总量的增加。在较小雨强条件下,公式计算土壤水渗漏总量稍大于HYDRUS模型计算,雨强较大时则相反。两种方法的计算结果在渗漏率峰值的出现时间和土层底部初始出流时间上存在差异。当土层厚度减小时,半经验解析式的计算精度有所提高,在使用该解析式时,建议对土壤层分层计算,可以提高计算精度。     

Simulated soil temperature and moisture at a clearcutting in central Sweden

Soil water and temperature measurements were made at a clearcutting in Jädraås, central Sweden, to give appropriate information for nutrient flow calculations and soil biological research. Compared to uncovered plots, slash‐covered plots were 1–2°C colder and had 3–6 volume percent higher water content in the 5 cm thick humus‐layer during the growing season following cutting. Relative to air, soil temperatures became warmer at both treatments during the second season and differences between uncovered and covered plots decreased. Tension dynamics in the mineral soil was most pronounced in uncovered plots, especially during the first dry growing season. The physically based model, SOIL, was used to analyse these observations and to estimate the effects of clearcutting. Simulated snow and frost depths, soil temperatures, water contents and tensions as well as ground water table were compared with measured data during a period of one to four years. Physical parameter values were estimated from independent measurements and by subjective optimization. Simulated soil water dynamics revealed the importance of hysteresis and vapour flows in sandy forest soils. The hydrological clearcutting effect as estimated from mature Scots pine evapotranspiration properties showed a 50% reduction of evapotranspiration, an increased soil water storage (0–1 m) of up to 120 mm and an increased percolation of 125 mm per year.     

Characterization of Aspen ASH,Sand and Log-Yard Waste Mixtures from an Aspen-Based Oriented Strand Board Mill for Use as an Intermediate Landfill Cover

Wood ash has a variety of uses including land application, geotechnical construction and daily and final covers for landfills. The objective of this study was to determine the relevant chemical and physical properties of selected mixtures of aspen burner-ash, log-yard waste scrapings (sandy soil plus wood waste) and a sandy soil as an intermediate landfill cover. The treatment mixtures, per weight basis, included: (1) 100% sand; (2) 80/20 log-yard waste/ash; (3) 50/50 sand/ash; (4) 40/30/30 sand/log-yard waste/ash; (5) 60/40 ash/log-yard waste; (6) 100% ash; (7) 100% log-yard waste. All treatments containing ash had a very high pH (12.8–13.3) and electrical conductivity (39–105 dS m^–1). The ash contained significant amounts of beneficial nutrients, but soil solution dominance by sodium carbonate suppressed concentrations of calcium and magnesium. Treatments containing ash showed lower bulk densities but relatively higher soil strength values (2.5–3.5 kg cm^–2) than that for the log-yard waste scrapings or the sandy soil, due to its self-cementing properties. Mixtures of soil material and ash had lower hydraulic conductivity rates (1.0 × 10^–4 cm s^–1) and lower infiltration rates compared to the sandy soil (5 × 10^–3 cm s^–1) or log-yard waste scrapings or pure ash. Water holding capacity increased with treatments containing ash. A soil–water balance model used to determine percolation rates through a 60 cm layer of treatment material showed that treatments containing a mixture of ash and soil material decreased the downward flow of water throughout the year.     

Impact of water percolation on nutrient leaching from an irrigated paddy field in Japan

Abstract. We examined the effect on soil nutrient status and sustainability of water percolation through an irrigated paddy field in Japan, to the depth of drainage (40 cm). The difference between amounts of nutrients leached by percolation and those supplied by irrigation indicated that 25–130 kg ha⁻¹ Ca, 8–24 kg ha⁻¹ Mg, from −1 to 9 kg ha⁻¹ K, and 8–17 kg ha⁻¹ Fe, respectively, were lost each year from the 0–40 cm soil layer during rice cultivation, when the supply from fertilization and rainfall and the loss in grain harvest were not accounted for. When the supply of K from rainfall and the loss in grain harvest were taken into account, a total K loss of about 10 kg ha⁻¹ was estimated. The electrical neutrality of inorganic ions in the percolating water was always maintained. From these results we estimate that the amounts of exchangeable Ca and Mg in the soil to a depth of 40 cm would decrease by 50% within 50–260 and 30–100 years, respectively, if similar management were continued without fertilization. The total amount of carbon dioxide (ΣCO₂) leached in percolating water during the period of rice cultivation was 120–325 kg C ha⁻¹, which corresponded to 0.47–0.94% of the soil organic carbon to 40 cm depth.