SR型野外人工模拟降雨装置

SR型人工降雨装置是一种多喷头、多单元组合式的间歇降雨装置.选用目前国内外较理想的喷头,在喷头处辅以可改变喷头降水方式的机械传动装置,以间歇方式降雨来满足其降雨强度,雨滴直径大小及其分布与自然降雨相似.每个单元的有效降雨面积为2m×5m;如果4个单元组合成,其长度可增加4倍,有效降雨面积即2m×20m.装置采用轻型铝合金材料制成,结构简单,易于安装拆卸,适用于野外工作.     

Development and testing of a model for predicting tillage effects on nitrate leaching from cracked clay soils

Both water movement and nitrate leaching in structured soils are strongly influenced by the nature of the macro-porosity. That macro-porosity can however also be manipulated by choice of tillage operations. In order to investigate the potential impacts of tillage on rates of nitrate leaching from structured soils, a model specific to these soils, CRACK-NP was developed. The model, its application and validation for an experimental site on a heavy clay soil (Verti-Eutric Gleysoil) at Brimstone Farm, Oxfordshire, UK, is described. The model considers the soil as a series of aggregates whose size is also the spacing of the macro-porosity. Water and solutes move in the macro-pores, but within the peds they move only by diffusion, internal infiltration and root uptake (evaporation). The model reflects the influence of diffusion limitation in the release of solutes to by-passing water. The model was then used to investigate the influence of variable ped spacings which were created by variations in tillage practices. The results both from the model and from the field data demonstrated that finer soil structures, which have larger surface contact areas and shorter diffusion path lengths, present greater opportunities for interaction between peds and the water moving around them, and so release more nitrates through the drainage waters.     

The effect of crop residue incorporation date on soil inorganic nitrogen, nitrate leaching and nitrogen mineralization

 Delaying cultivation and incorporation of arable crop residues may delay the release of NO₃ ^– and hence reduce leaching. The objective of this study was to investigate the effect of timing of cultivation on the mineralization and leaching of NO₃ ^– from an arable crop residue. Overwinter N leaching and periodic measurements of soil inorganic N were combined to estimate net N mineralized after ploughing a crop residue into a free-draining loamy sand soil in central England on six dates from June 1994 to January 1995. The crop residue was whole green barley with approximately 2% N. N leaching in the two following winters was increased by the addition of crop residues. Early residue application also tended to increase N leached in the first winter, largely as a consequence of relatively large losses early in the drainage period. Thus, early incorporation of crop residues presents a greater leaching risk. The amount of N leached in the second (drier) winter was similar for all dates of incorporation. At the end of the first winter, inorganic N derived from the crop residue was greatest for earlier additions: June (40% N applied) > September (30% N applied) > August (20% N applied) > October (19% N applied) > November (11% N applied) > January (3% N applied). However, at the end of the experiment, there was no evidence that the residues which had mineralized least by the end of the first winter had, to any significant degree, caught up, and this was confirmed by the parameters of the equation for first-order decomposition in thermal time. These results indicate that the effect of temperature, particularly in the early stages of residue mineralization, is complex and interacts with other soil processes in terms of the fate of the N mineralized. Received: 19 July 1999     

田块尺度上土壤/地下水中硝态氮动态变化特征及模拟

以青岛市大沽河下游地区冬小麦–夏玉米轮作农田为对象,通过田间试验和室内分析,研究了不同深度土壤和地下水中NO3–-N在一个轮作周期内的动态变化特征,探讨了不同氮肥施用量和灌溉量对土壤-地下水系统中NO3–-N时空分布的影响,并基于土壤水动力学和溶质运移理论对土壤中NO3–-N运移过程进行了数值模拟。模拟结果表明:小麦季施氮(N)量达到380 kg/hm2,玉米季施氮量达到290 kg/hm2时,季末剖面深度130~160 cm土壤NO3–-N含量超过10 mg/kg;由地下水NO3–-N月累计量估算模型得出,NO3–-N在6月和8月向浅部地下水的淋失量最大,分别为7.20、7.67 mg/L。     

波涌灌间歇入渗饱和-非饱和土壤水分运动数值模拟及试验

考虑到地下水浅埋对上层包气带水分分布造成一定影响,该研究结合波涌灌技术,对地下水浅埋下间歇入渗的土壤水分分布特征和运动规律进行了分析,建立了基于饱和-非饱和土壤条件下一维间歇入渗水分运动模型,根据试验实测资料采用Hydrus-1D软件反推土壤水分运动参数,并对入渗过程进行了模拟。在此基础上,确定了饱和导水率的估算模型。结果表明:所建参数估算模型较好地反映了饱和导水率与间歇周期数、循环率以及周期时间之间的相关关系,所建水分运动模型模拟值与实测值比较,累计入渗量、土壤含水率以及湿润体运移距离总体相关系数高于0.96,均方差在0.5以内,吻合度较高,能够较好地描述了地下水影响条件下波涌灌间歇入渗饱和-非饱和土壤水分运动特征。该研究为波涌灌技术进一步发展奠定了科学基础。     

The effectiveness of cover crops during eight years of a UK sandland rotation

Abstract. Growing cover crops during the winter before spring-planted crops is often suggested as an effective method to decrease nitrate leaching. A four-course crop rotation (potatoes-cereal-sugarbeet-cereal) was followed through two rotations on a sandy soil in the English Midlands. Three management systems were imposed on the rotation to test their effects on nitrate loss. The effects of cover crops on nitrate leaching and crop yields were compared with the more conventional practice of over-winter bare fallow before potatoes and sugarbeet.
Cover crop N uptake was variable between years, averaging 25 kg ha⁻¹, which is typical of their performance on sandy soils in the UK. The cover crops usually decreased nitrate leaching but their effectiveness depended on good establishment before the start of drainage. Over 7 years, cover crops decreased the average N concentration in the drainage from 24 to 11 mg l⁻¹. Potato yield and tuber N offtake increased after cover crops. Ware tuber yield increased by an average of c . 8%; this was unlikely to be due to additional N mineralization from the cover crop because the potatoes received 220–250 kg fertilizer N ha⁻¹, and non-N effects are therefore implicated. Sugar yield was not increased following a cover crop.
After 8 years of nitrate-retentive practices, there were no measurable differences in soil organic matter. However, plots that had received only half of the N fertilizer each year contained, on average, 0.14% less organic matter at the end of the experiment.     

Proton release by N2‐fixing plant roots: A possible contribution to phytoremediation of calcareous sodic soils

With a world‐wide occurrence on about 560 million hectares, sodic soils are characterized by the occurrence of excess sodium (Na⁺) to levels that can adversely affect crop growth and yield. Amelioration of such soils needs a source of calcium (Ca²⁺) to replace excess Na⁺ from the cation exchange sites. In addition, adequate levels of Ca²⁺ in ameliorated soils play a vital role in improving the structural and functional integrity of plant cell walls and membranes. As a low‐cost and environmentally feasible strategy, phytoremediation of sodic soils — a plant‐based amelioration — has gained increasing interest among scientists and farmers in recent years. Enhanced CO₂ partial pressure (P_CO2) in the root zone is considered as the principal mechanism contributing to phytoremediation of sodic soils. Aqueous CO₂ produces protons (H⁺) and bicarbonate (HCO₃^‐). In a subsequent reaction, H⁺ reacts with native soil calcite (CaCO₃) to provide Ca²⁺ for Na⁺ Ca²⁺ exchange at the cation exchange sites. Another source of H⁺ may occur in such soils if cropped with N₂‐fixing plant species because plants capable of fixing N₂ release H⁺ in the root zone. In a lysimeter experiment on a calcareous sodic soil (pH_s = 7.4, electrical conductivity of soil saturated paste extract (EC_e) = 3.1 dS m^‐1, sodium adsorption ratio (SAR) = 28.4, exchangeable sodium percentage (ESP) = 27.6, CaCO₃ = 50 g kg^‐1), we investigated the phytoremediation ability of alfalfa (Medicago sativa L.). There were two cropped treatments: Alfalfa relying on N₂ fixation and alfalfa receiving NH₄NO₃ as mineral N source, respectively. Other treatments were non‐cropped, including a control (without an amendment or crop), and soil application of gypsum or sulfuric acid. After two months of cropping, all lysimeters were leached by maintaining a water content at 130% waterholding capacity of the soil after every 24±1 h. The treatment efficiency for Na⁺ removal in drainage water was in the order: sulfuric acid > gypsum = N₂‐fixing alfalfa > NH4NO3‐fed alfalfa > control. Both the alfalfa treatments produced statistically similar root and shoot biomass. We attribute better Na+ removal by the N₂‐fixing alfalfa treatment to an additional source of H⁺ in the rhizosphere, which helped to dissolve additional CaCO₃ and soil sodicity amelioration.     

漫灌淋洗暗管排水协同改良滨海盐土水盐时空变化特征

为揭示暗管排水下漫灌淋洗土壤水盐运移规律,改进灌排工程技术,提高灌排改良效果,该文应用Vedernikov入渗方程和Van der Molen淋洗脱盐方程,对滨海盐土灌排改良过程土壤水分入渗、淋洗水量分配、盐分时空变化特征等进行了模拟研究。结果表明,间距分别为3、6、9 m的暗管排水控制区域(0~1.5、0~3、0~4.5 m)田面漫灌稳定入渗强度分别在3.14~4.26、1.19~3.68和0.58~3.55 cm/d之间,排水暗管间距越大的田面土壤入渗强度空间变化也越大。暗管排水下田面漫灌入渗强度的空间变化导致淋洗水量空间分配不均,距暗管越近的区域分配的淋洗水量越多,也导致了土壤淋洗脱盐空间差异明显。漫灌淋洗20 d,间距9 m的暗管排水控制区域(0~4.5 m)仅靠近暗管0~0.6 m宽的区段0~60 cm土层土壤含盐量下降到3.00 g/kg以下,该区段(达到改良目标)仅占暗管排水控制区域面积的13.3%;漫灌淋洗40 d,仅靠近暗管0~1.6 m宽的区段0~60 cm土层土壤含盐量下降到3.00 g/kg以下,该区段(达到改良目标)仅占暗管排水控制区域面积的35.5%;为了使暗管排水控制区域0~60 cm土层土壤含盐量都下降到3.00 g/kg以下,需要漫灌淋洗100 d。完全一致地漫灌淋洗整个区域将导致暗管附近区域土壤过度淋洗,浪费水资源;而距暗管较远区域土壤淋洗不充分,降低淋洗效率。     

Measurement of Fertilizer Leaching from the Root Zone Using an Automated Infiltration Soil Water Sampler in an Unsaturated Sandy Field

In sandy fields with vegetable cultivation, fertilizer leaching may occur and it should be well-controlled. The development of a direct soil water sampler is necessary to examine solute transport and fertilizer leaching in the vadose zone, since soil water reflects timely monitoring of data more accurately than groundwater. We developed a Suction-Controlled Flux Sampler to collect infiltration soil water in a sandy soil. In the present study, we monitored fertilizer leaching in an unsaturated sandy field during the rainy season, while evaluating the sampling performance of SCFS for the sampling of infiltration water. SCFS directly collected the infiltration water effectively over a period of several months in the sandy field and recorded the Water-Collecting Efficiency from 92 to 115% under various infiltration conditions during a period of 50 d. WCE was affected by the rainfall intensity as well as by previous rainfall, which enhanced WCE. The results obtained from the use of SCFS and several sensors demonstrated that the amount of leached water remained low as long as irrigation was applied according to the cultivation manual. However, an unexpected heavy rainfall event led to fertilizer leaching. The fertilizer leaching trend was effectively monitored by several sensors inserted into the soils, while detailed analysis of the components was performed after collection by using SCFS. Direct access to infiltration water enabled to examine the infiltration process and detailed variations in the amounts of discharged anions. The sensor-equipped monitoring system together with SCFS is suitable for precise management of fertilizer and irrigation application.     

亚热带花岗岩地区土壤矿物风化过程中盐基离子的释放特征

矿物风化过程中盐基离子释放遵从一定的化学计量关系,这种化学计量关系一般只能通过模拟实验来获取。本研究采用pH 7.0的EDTA-乙酸铵溶液将土壤中的交换性盐基离子完全洗脱出来,然后用Batch方法模拟不同pH溶液淋溶洗脱盐基和未洗脱盐基土壤,旨在消除土壤中交换性盐基离子的影响后更为准确地判断土壤矿物风化的盐基离子释放特征。结果表明:未洗脱盐基土壤的淋出液pH由3.73±0.14逐渐上升到4.23±0.06,主要原因是淋溶液中有高浓度的NH_4~+;洗脱盐基土壤矿物风化后淋出液pH从7.39±0.02逐渐下降到5.39±0.17,主要是由于土壤中可风化矿物减少。土壤交换性盐基离子会改变盐基离子释放特征、释放总量:未洗脱盐基土壤经酸雨淋溶后,各盐基离子释放均呈现急速下降后逐渐平缓的趋势,洗脱盐基土壤矿物风化后,K~+及盐基离子释放总量呈波动上升趋势,且盐基离子释放总量比未洗脱盐基土壤低。土壤交换性盐基离子的存在还会改变淋出液中的盐基离子化学计量关系:未洗脱盐基土壤的K~+︰Ca~(2+)︰Mg~(2+)︰Na+化学计量关系为11︰13︰4︰1(当量比),而洗脱盐基土壤为7︰2︰2︰1。K~+是盐基离子中风化释放量最多的,大部分K~+来自于土壤中云母的风化。因此,只有利用洗脱盐基土壤的盐基离子释放量才能准确计算矿物风化速率并获得准确的化学计量关系。土壤矿物风化作用随着淋溶液酸度增大而增强,但模拟一年降雨量的情况下,p H 3.5、4.5和5.5三种不同p H溶液对矿物风化后盐基离子的释放在实验期间没有显著性影响,较长时间后的差异性有待观察。本研究表明,可以通过预洗脱盐基土壤然后模拟酸雨淋溶的方法,观察矿物风化特征,特别是盐基离子释放的化学计量特征。