基于ECH_2O的覆膜对土壤水热状况影响的试验研究

为研究覆膜对土壤水热运移的细微影响,利用土壤水热盐自动监测系统(ECH2O)对西北干旱区的玉米地进行了高分辨率的定点连续监测。发现覆膜对改善土壤表层水热状况有显著效果,覆膜处理下表层土壤含水量低于不覆膜处理,地温高于不覆膜处理对应值。在10cm深度,覆膜处理的土壤含水量较不覆膜处理低;而在20cm及40cm深度,覆膜处理的土壤含水量较不覆膜处理高。覆膜对不同深度地温均有提升作用,但在玉米不同生育阶段其影响程度不同:覆膜对地温的影响在生育末期最为显著;在10cm深度,覆膜处理的地温高于不覆膜处理,在40cm和60cm深度,差异较小。     

不同水土保持模式下坡耕地的土壤水分特征

针对松嫩平原北部丘陵漫岗区坡耕地存在的干旱与水土流失并存的问题,选取了垄向区田、鼠道、鼠道+暗管、鼠道+垄向区田、鼠道+暗管+垄向区田、常规耕作等6种水土保持技术模式,研究了土壤水分变化特征。结果表明,从整体上看,不同水土保持技术模式0～100cm土层土壤储水量与时段降雨量变化趋势一致,土壤储水量大小的技术模式依次为,鼠道+暗管+垄向区田>鼠道+垄向区田>垄向区田>鼠道+暗管>鼠道>常规耕作。各水土保持技术模式的总蒸散量大小依次为:鼠道+暗管+垄向区田>鼠道+垄向区田>鼠道+暗管>鼠道>垄向区田>常规耕作。研究结果为松嫩平原北部丘陵漫岗区坡耕地水土保持技术模式的合理选择提供依据。     

设施条件下膜孔灌土壤水氮运移分布特性研究

在室内进行了模拟设施条件下膜孔灌灌施硝酸钾肥液试验,分析测定了灌后不同时间的土壤含水量和硝态氮质量分数。研究表明,土壤含水率和硝态氮质量分数随着灌后时间延长逐渐减小,土壤水分和硝态氮在灌后1d内存在明显减少现象,灌后5d土壤硝态氮反硝化作用加强;土壤含水率和硝态氮存在耦合现象,二者分布趋势基本相同,以膜孔中心为最大,远离膜孔中心逐渐减小。     

Soil erosion under different harvesting managements in steep forestlands from northern Spain

In spite of the high risk of erosion, highly mechanized operations, in which humus layer removal and down-slope ploughing are practised, are often employed to prepare steep forestlands for planting. The purpose of this study was to evaluate the effect on soil loss of three post-harvesting management systems usually used in a mountainous region of northern Spain. The techniques evaluated were (a) conventional stem-only harvesting, (b) whole-tree harvesting and humus layer removal and (c) whole-tree harvesting and humus layer removal followed by down-slope deep ploughing. Soil erosion was measured in a total of 39 recently clear-felled Pinus radiata plantations over the period between the stand harvesting and establishment of understorey vegetation. They were located on slopes with gradients of between 40 and 50 per cent. For all treatments the associated runoff–rainfall ratios were high, indicating inherent low permeability of the soil. Intense site preparation resulted in considerable decreases in soil organic matter and increases in bulk density, which decreased the hydraulic conductivity and subsequently produced higher runoff. These deteriorations of soil properties delayed the establishment of pioneer vegetation thus extending the period of high erosion. In the ploughed soils, the higher soil erodibility and the removal of slash and vegetation cover resulted in a four-fold increase of soil losses when compared with no mechanical site preparation. The results indicate that, in order to maintain the soil productivity, and for conservation purposes, harvesting management should minimize the soil disturbances and maintain the slash and vegetation cover. Copyright © 1999 John Wiley & Sons, Ltd.     

重庆酸性紫色土马铃薯的高产优质与养分平衡

Over a period of two years,field experiments were conducted on four silty loam soils grown with foliar vegetable crops inculding Chinese cabbage(Brassica pekingensis Rupr.,cv.Lu-Bai 3),autumn greens (B.chinensis L.,cv.Piao-Geng-Bai),winter greens(B.var.rosularis Tsen et Lee,cv,You-Dong-Er),and summer greens(B.chinensis L.,cv.Zao-Shu5),respectively,Each eperimpent included one CK treatment without K,N and Pfertilizers applied,and four treatments with from low to high doses,0-300 kg hm^-2 for Chinese cabbage,0-150 kg hm^-2 for autumm and winter greens and 0-180 kg hm^-2 for summer greens,of K fertilizers in the form of sulfate of potash(SOP)applied together with N and P fertlizers,One treatment of K fertilizer in the form of muriate of potash(MOP) applied at high levels(150 or 180 g hm^-2)together with N and P fertilizers was included in the experiments of autumn,winter and summer greens ,respectively,in order to compare the effcts of SOP and MOP ,The market yields of the tested crops incresaed significantly with the increasing rate of K application.The crops supplied with K fertilizers yielded more stably as the CV% of their yields decreased with the rate of K application.K fertilization increased not only K contents but also the amounts of N ,P and K absorbed in shoots of autumn,winter and summer greens,which were atatistically significantly correalted to their yields.In can aslo be found that potassium improved the quality of the foliar vegetable crops as their dry mater contents were generally increased and Vc contents obviously increased and nitrate contents markedly decreased ,As compared to MOP,SOP was more effective on the yields and quality of autumn,winter and summer greens at the high levels of fertilization.     

Influence of chloride and sulphate ions on soil enzymes

Ammonium chloride (AC) and ammonium sulphate (AS) are commonly used nitrogen fertilizers. But the effect of chloride and sulphate ions from these fertilizers on soil enzyme activity has received scant attention. Hence, we conducted a pot culture study to assess the influence of chloride (as AC) and sulphate (as AS) on the activities of urease, amidase, phosphatase and dehydrogenase in soil using rice as the test crop. Chloride and sulphate levels were fixed at 132, 264 and 396 kg ha⁻¹ respectively. Controls were also performed. The enzymes were assayed at three stages of the crop growth viz., active tillering, panicle initiation and harvest.
The enzyme activities decreased with increasing chloride and sulphate levels; however, the degree of inhibition varied among the enzymes assayed and the nature and amounts of salts added. The inhibition may be due to the specific effects of chloride and sulphate ions on microbial growth and subsequent enzyme synthesis, osmotic desiccation leading to microbial cell lysis, and a salting-out effect modifying the ionic conformation of the active site of the enzyme protein.     

Strip-till as a means of decreasing spatial variability of winter barley within a field scale

The tillage system, which joins soil tillage, fertilisation, and seed sowing in one pass of a machine, is rarely used in cereal cultivation. This research aimed to study whether strip-till and conventional tillage (post-harvest ripping and mixing of stubble, ploughing, pre-sowing fertilisation, and seedbed preparation) differ in plant density, yield components, and grain yield of winter barley cultivated on Cambisol in a region with low rainfall, the annual average is about 500?mm. To reach this aim, a two-year, large-plot experiment was conducted in a production field. The soil within the field was spatially variable in texture, moisture, and chemical and biological properties, CV 2.3% do 29.6%. Strip-till had lower within-field spatial variability of winter barley grain yield than conventional tillage. The standard deviation was 0.36?t?ha^?1, 0.67?t?ha^?1 in the first year and 0.12?t?ha^?1, 0.30?t?ha^?1 in the second year, respectively. During the period of limited rainfall, strip-till had greater uniformity of plants after emergence; after the winter with low air temperature and a low amount of snow, it had greater plant density. Thus, strip-till can reduce variability of plants and their yield within a field, especially in adverse environmental conditions.     

Evaluation of the spatial pattern of surface soil water content of a karst hillslope in Southwest China using a state-space approach

This study aims to evaluate the effects of soil physicochemical properties and environmental factors on the spatial patterns of surface soil water content (SWC) based on the state-space approach and linear regression analysis. For this purpose, based on a grid sampling scheme (10 m × 10 m) applied to a 90 m × 120 m plot located on a karst hillslope of Southwest China, the SWC at 0–16 cm depth was measured 3 times across 130 sampling points, and soil texture, bulk density (BD), saturated hydraulic conductivity (K_s), organic carbon (SOC), and rock fragment content as well as site elevation (SE) were also measured at these locations. Results showed that the distribution pattern of SWC could be more successfully predicted by the first-order state-space models (R² = 67.5–99.9% and RMSE = 0.01–0.14) than the classic linear regression models (R² = 10.8–79.3% and RMSE = 0.11–0.24). The input combination containing silt content (Silt), K_s, and SOC produced the best state-space model, explaining 99.9% of the variation in SWC. And Silt was identified as the first-order controlling factor that explained 98.7% of the variation. In contrast, the best linear regression model using all of the variables only explained 79.3% of variation.     

Reduction of soil heavy metal bioavailability by nanoparticles and cellulosic wastes improved the biomass of tree seedlings

The purpose of this study was to use zero‐valent iron nanoparticles (nZVI) and cellulosic wastes to reduce bioavailability of lead (Pb) and cadmium (Cd), and to establish Persian maple seedlings (Acer velutinum Bioss.) in contaminated soil. One‐year‐old seedlings were planted in pots filled with unpolluted soil. Lead [Pb(NO₃)₂] and Cd [Cd(NO₃)₂] were added with concentrations of 0 (Control), 100 (Pb100), 200 (Pb200), and 300 (Pb300) mg kg⁻¹ and 10 (Cd10), 20 (Cd20), and 30 (Cd30) mg kg⁻¹. Cellulosic wastes were mixed with soil at the same time of planting [four levels: 0, 10 (W1), 20 (W2), 30 (W3) g 100 g⁻¹ soil]. The nZVI was prepared by reducing Fe³⁺ to Fe⁰ and injected to pots [four levels: 0, 1 (N1), 2 (N2), and 3 (N3) mg kg⁻¹]. Height, diameter, biomass, tolerance index of seedlings, bioavailability of heavy metals in soil, and removal efficiency of amendments were measured. The highest values of seedling characteristics were observed in N3. The highest removal efficiency of Pb (Pb100: 81.95%, Pb200: 75.5%, Pb300: 69.9%) and Cd (Cd10: 92%, Cd20: 73.7%, Cd30: 68.5%) was also observed in N3. The use of nZVI and cellulosic waste could be a proper approach for seedling establishment in forests contaminated with heavy metals.