人工模拟降雨供水水质对坡面产流产沙的影响

利用黄土高原2种典型的土壤类型(黄土和塿土),在2个降雨强度(45.5,95.5mm/h)和2个坡度(8.7%,25.9%)条件下进行了人工模拟降雨试验,研究了3种水质(去离子水、自来水、盐水)对坡面产流、产沙过程的影响。结果表明,2种土壤类型的产流过程差异显著,黄土条件下去离子水最先产流,但产流速率小于自来水与盐水;而塿土条件下去离子水的产流速率始终最大,自来水与盐水由于离子数量相当,产流速率差异较小。水质主要通过地表结皮的形成与发育影响径流,以总降水量45.5mm为例,径流深随供水电导率的增大而减少,与去离子水相比,黄土条件下自来水和盐水的径流分别减少了5.7 mm和1.5mm,而塿土条件下分别减少了7.2mm和9.8mm。受产流过程的影响,不同供水水质条件下产沙过程不一,产沙速率与产流速率变化同步。2种土质条件下产沙量均是去离子水最大,与去离子水相比,自来水和盐水分别减少了45.9%,35.8%(黄土)和65.6%,68.3%(塿土),结果显示模拟降雨水质会显著影响坡面产流产沙过程,为保证试验数据的准确性和可对比性,建议在进行人工降雨相关试验时均采用去离子水。     

Is mechanical soil aeration a strategy to alleviate soil compaction and decrease phosphorus and suspended sediment losses from irrigated and rain‐fed cattle‐grazed pastures?

Agriculture is a major source of phosphorus (P) and suspended sediment (SS) losses to aquatic ecosystems promoting eutrophication. Mechanical soil loosening equipments such as topsoil looseners or aerators have been reported to improve the physical quality and infiltration of soils susceptible to livestock damage resulting from treading. We hypothesized that soil aeration would significantly decrease the volume of surface runoff and consequent losses of P and SS compared with non‐aerated soil (control) in cattle‐grazed pasture on a poorly structured silt‐loam soil. Hydrologically isolated plots (2 m long × 1 m wide × 0.15 m deep) were installed in aerated and control plots to collect surface runoff following irrigation or rainfall and analysed for P and SS losses for 1 year. Soil physical properties [% macroporosity, bulk density, saturated hydraulic conductivity (K_sat) and unsaturated hydraulic conductivity (K_unsat at ?1kPa)] were measured in the aerated and control treatments and taken before each irrigation event (n = 12). Six months after mechanical aeration was employed, but before cattle grazing commenced, no significant differences in soil physical quality were found between aerated and control treatments, with the exception of a minor increase in K_unsat for the control plots. This lack of treatment difference continued after grazing and was largely attributed to the re‐settling of the poorly structured and dispersive soil. Flow‐weighted mean concentrations and annual loads of dissolved reactive P (DRP) on the mechanically aerated soil (2.24 kg DRP/ha) were approximately double those from the control treatment (1.20 kg DRP/ha). However, no significant differences were observed between treatments for surface runoff volumes and losses of total P and total SS, which may reflect the similar soil physical conditions exhibited between treatments throughout most of the trial. As observed elsewhere, time (days) since grazing or fertilizer application was found to influence P and/or SS losses. We conclude that aeration did not decrease P and SS losses. Any changes in soil physical properties such as macroporosity were short‐lived and therefore unlikely to influence surface runoff and subsequent P and SS losses for this soil type.     

Phosphorus losses from arable land in England

Abstract. Concentrations and annual loadings of molyhdate reactive P (MRP) and total (including particulate) P (TP) are reported from field drainage, catchment and erosion experiments in England. Annual losses through field drains and in catchment runoff were 0.037-0.74 kg MRP/ha and 0.37-2.64 kg TP/ha, but those in surface runoff from experimental plots measuring erosion were generally much greater (often > 3 kg MRP/ha and up to 32 kg TP/ha in a wet year). Amounts of TP in drainflow and catchment runoff depended upon factors influencing soil dispersibility, such as particle size distribution and calcium carbonate content. The results to date suggest that P losses in surface runoff and erosion from arable fields to water are best limited by: (a) maximizing crop cover, using minimal cultivation practices and where possible planting crop rows across rather than up and down the slope, (b) avoiding cultivation practices that result in dispersion of soil particles, and (c) avoiding application of P fertilizer to wet soils when rainfall is likely soon after application. Consideration should he given to maintaining field drains below peak efficiency to reduce subsurface P losses.     

江西省雨水、灌溉水及渗漏水中的硫对土壤硫的影响

Ten rainfall and irrigation water-collecting posts were set up in different ecotype districts of Jiangxi Province,China,to quarterly measure S content in rainfall and irrgation water.A rasinwater chemical composition-collecting device was used to collect the sulphur in rainfall,and the amount of sulphur adsorbed on the resin column in the device was determined.The soil percolating water was gathered using 6 lysimeters built up according to the profile sequence of the red soil derived from red sandstone and the red soil derived from Quaternary red clay,separately.On the lysimeters peanuts,soybean and radish were grown in rotation.Two treatments were designed:without S addition and with S additin at a rate of 14kg S ha^-1,The SO4^2- contents in rainfall,irrigation water and soil percolating water were determined by the turbidimetry.The results in 1997 showed that the average annual S content in rainwater ws 28.13kg S ha^-1.the average S content in irrigation water was 1.7mg S L^-1,and the average content of SO4^2- in soil percolation water was 2.30kg Sha^-1 year^-1 and 4.70 kg Sha^-1 year^-1 in treatments without and with sulphur application,respectively,In Jiangxi Province,apart from the losses by runoff and leaching,the sulphur in rainfall avaliable to crops is 7.3kg S ha^-1 year^-1 and additional S application is required.When rice is grown.however,irrigation water can suply 6.9kg S ha^-1,which,along with the sulphur in rainfall,cal almost meet the S requirement of one cropping of rice.     

Factors Influencing Runoff P Losses from Farmlandsof the Dianchi Lake Watershed in Yunnan, China

Effects of factors such as slope, surface soil texture, fertilization and crop cover with different rainfall intensitieson phosphorus (P) losses in farmland runoff of the Dianchi Lake Watershed in Yunnan Province of China were studiedthrough a rainfall simulation test using a red soil, one of the most widely distributed soils of the study area. Resultsshowed that the runoff concentrations of total phosphorus (TP) and P losses differed with the slope, being highest whenthe slope was 18~. At two different rainfall intensities, the runoff TP and P losses had a similar decreasing trend asthe surface soil texture became coarser, therefore applying the grit would decrease P in runoff from soils of farmland onslopes with heavier textures. With wheat as a crop cover the runoff TP concentrations and P losses were significantlylower than those of the bare soil. This showed that plant cover would greatly decrease P in runoff from the farmland ofthe study area. The TP concentration in runoff from the soil two days after fertilization doubled when compared withthat from the non-fertilized soil, indicating that fertilization could mean a dramatic rise in P runoff if irrigation or heavyrainfall occurred immediately after application and that no fertilization before a rain and no irrigation immediately afterfertilization would reduce runoff P loss from the farmland of the study area.     

屋顶花园雨水利用系统设计与实践

该文意在探讨利用屋面雨水对屋顶花园进行灌溉的可行性。以北大荒集团某酒店屋顶花园为例,从植物需水量、雨水可收集量、蓄水池容量及雨水收集系统等方面进行屋面雨水回收利用设计,利用彭曼-蒙特斯公式计算屋顶花园植物需水量,结果表明:5-10月屋顶花园植物需水总量为3521.78m3,各月份间差异较大,10月份量最小仅为361.8m3,6月份量最大为729.6m3;同期可收集屋面雨水总量为2179.3m3,并据雨水径流总量与初期弃流量产生的径流量设计蓄水池容量为131m3;将收集雨水全部用于屋顶花园绿地灌溉,能节省61.88%灌溉用水;据此,采用工程技术为屋顶花园设计雨水收集系统及自动灌溉系统,对屋顶花园雨水收集量与灌溉量的水量平衡分析结果表明:利用该自动灌溉系统可节约灌溉用水67.20%,雨水利用率可达54.55%,该设计对北方干旱地区屋顶花园雨水回用技术设计具一定的实用价值和应用前景。     

中国云南滇池流域农田径流磷污染负荷影响因素研究

Effects of factors such as slope, surface soil texture, fertilization and crop cover with different rainfall intensities on phosphorus (P) losses in farmland runoff of the Dianchi Lake Watershed in Yunnan Province of China were studied through a rainfall simulation test using a red soil, one of the most widely distributed soils of the study area. Results showed that the runoff concentrations of total phosphorus (TP) and P losses differed with the slope, being highest when the slope was 18°. At two different rainfall intensities, the runoff TP and P losses had a similar decreasing trend as the surface soil texture became coarser, therefore applying the grit would decrease P in runoff from soils of farmland on slopes with heavier textures. With wheat as a crop cover the runoff TP concentrations and P losses were significantly lower than those of the bare soil. This showed that plant cover would greatly decrease P in runoff from the farmland of the study area. The TP concentration in runoff from the soil two days after fertilization doubled when compared with that from the non-fertilized soil, indicating that fertilization could mean a dramatic rise in P runoff if irrigation or heavy rainfall occurred immediately after application and that no fertilization before a rain and no irrigation immediately after fertilization would reduce runoff P loss from the farmland of the study area.     

城市雨水对生菜产量品质与重金属含量的影响

作为都市农业灌溉用水,城市雨水对农产品食品安全和营养品质的影响深受关注。论文收集自然雨水(T1)、屋顶雨水(T2)和路面雨水(T3),静置沉淀后配置营养液进行水培生菜种植,测量生物产量、生理指标(叶绿素含量、净光合速率、根系活力)、营养指标(可溶性糖、可溶性蛋白、维生素C、硝酸盐)和元素含量(Ca、Fe、Mg、Zn、As、Cd、Pb),结果表明:城市雨水重金属含量低于国家标准,可以作为农业灌溉用水;雨水栽培生菜比自来水栽培生菜长势弱、产量低,路面雨水栽培生菜产量最低,单株干质量仅为3.57 g;雨水降低了生菜叶绿素含量和净光合速率,提高了生菜根系活力,屋顶雨水生菜和路面雨水生菜根系活力分别为3.17和4.08 mg/(g·h),雨水栽培生菜的根冠比大于自来水生菜;雨水栽培生菜蛋白质、糖类和Vc含量不比自来水栽培生菜低,自然雨水生菜蛋白质质量分数4.97 mg/g,路面雨水生菜可溶性糖含量1.00%,路面雨水生菜Vc含量1.52 mg/g,分别为各项指标的最高值;供试生菜硝酸盐含量分别为5.62、5.48、6.04和7.04 mg/g,都超过了国家标准3.00 mg/g,这与试验采用1倍剂量营养液和采用硝酸调节p H值有关;雨水生菜有益元素Ca、Mg含量高于自来水生菜,Fe含量低于自来水生菜,雨水生菜总体品质略好于自来水生菜;自来水、自然雨水、屋顶雨水和路面雨水栽培生菜含As量分别为5.83、4.10、4.53和4.60μg/kg,含Cd量分别为0.76、0.78、2.59和1.37μg/kg,含Pb量分别为102.37、118.63、151.53和123.37μg/kg,远小于国家限量值,满足食品安全要求。总之,利用城市雨水作为都市农业灌溉用水,作物长势弱,产量低,但营养品质略好,食品安全,将城市雨水作为都市农业灌溉用水是可行的。     

Water management in various crop production systems related to soil tillage

Soil tillage, of different types and intensity and performed at different antecedent soil moisture conditions, is an important tool for agricultural water management. Tillage systems have important applications for increasing irrigation efficiency, enhancing the effectiveness of drainage systems, improving water quality, decreasing runoff losses and minimizing soil erosion, increasing runoff losses for water harvesting and supplemental irrigation, and decreasing percolation losses and creating aquatic environments for rice cultivation. The versatility and diversity of applications of tillage systems depend on the choice of tillage techniques. No-tillage methods with residue mulches are useful to conserve soil water. Chisel tillage and subsoiling methods along with ridge-tillage techniques are useful in increasing irrigation efficiency. No-tillage systems are useful in decreasing sediment density and transport of sediment laden pollutants in runoff, and puddling and wet tillage techniques or soil compaction are used in rice cultivation. Finally soil compaction and techniques to increase water repellence are useful for water harvesting for subsequent use in supplemental irrigation.     

Preferential water flows in meadow-chernozemic soil of the Saratov Transvolga region

The development of preferential gravity water flows in a leached meadow-chernozemic soil on stratified ancient alluvial deposits in the Saratov Transvolga region was studied using simple cell lysimeters in infiltration experiments. The measured lysimeter runoff within a horizontal section of a soil body comparable in size to the cross section of a cell lysimeter varied from completely absent to a rather intense. Depending on changes in the lysimeter runoff rate during the infiltration stages, the pore space continua with uniform, stable functioning and those with varying functioning (increasing or decreasing runoff) can be distinguished in a soil body. Labeling experiments showed that a decrease in the rate of lysimeter runoff to the cell was accompanied by an increase in the dilution of irrigation water with pore solutions.     

基于水量平衡的红壤丘岗坡地利用结构拟合

以集雨区水量平衡为基础,从分析坡地水文过程入手,以坡地不同生态系统雨水分配、降雨过程地表径流产量、径流过程的土壤及养分流失量为参数,以生产灌溉对集雨的要求、坡地不同生态系统对雨水侵蚀的承载力、坡地雨水运移过程对环境和区域洪涝灾害的影响为约束条件,拟合出红壤丘岗坡地农林复合生态系统构建适宜的土地利用结构:人工林占30%,人工草地占15%,果药茶园占30%,耕地占20%,自然保护区占5%。该用地比例(结构)既满足于地貌单元(集雨区)生态系统利用坡地集雨维持系统水循环平衡的要求,也满足于坡地农林复合生态系统的可持续性保护的要求。     

Parameterization of the Effect of Bench Terraces on Runoff and Sediment Yield by Swat Modeling in a Small Semi‐arid Watershed in Northern Tunisia

In Tunisia, soil and water conservation interventions are among the most practicable strategies to prevent and mitigate rainwater losses through surface runoff and consequential erosion of fertile soils. In this study, a small and terraced agricultural catchment (Sbaihia) was used as an experimental site to analyze and parameterize the effects of bench terraces on water and sediment yield using the Soil and Water Assessment Tool. Model calibration and validation was performed, taking advantage from high‐quality daily runoff data from 1994 to 2000 and a high‐resolution bathymetric survey of the hill lake at the watershed outlet. Soil and Water Assessment Tool indicated that the local terraces, established on approximately 50% of the watershed area, reduced surface runoff by around 19% and sediment yield by around 22%, decelerating the siltation of the hill lake. Targeted model calibration delivered concise parameter set describing bench terrace impacts on runoff (Soil Conservation Service curve number method) and sediment yield (Modified Universal Soil Loss Equation) crucial for outscaling of soil and water conservation impacts and suitable watershed management. Copyright © 2016 John Wiley & Sons, Ltd.     

脱硫石膏对土壤磷流失的阻控效应及机制试验

研究脱硫石膏(flue-gas desulfurization gypsum,FGDG)对土壤磷流失的阻控效果,既有利于开拓FGDG资源化利用新途径,又有助于丰富农业面源磷流失控制工程技术。借助土柱淋溶试验和人工边坡降雨侵蚀模拟试验,针对上海某火电厂的FGDG,系统研究不同质量配比(0、1%、2.5%和5%)的FGDG对农田土壤的固磷效果及机理。结果表明:1)FGDG的Ca2+将溶解态P转化成难溶态P,并将土壤无机磷中的Ca2-P、Al-P转化成Ca8-P和Ca10-P,有效控制溶解态磷(total dissolved phosphorus,TDP)直接流失,与对照组相比,施加FGDG对淋洗土柱TDP流失的阻控率达到92.8%~94.8%,而添加FGDG的各处理间无显著差异(P0.05);2)添加FGDG后,土壤的渗透性能和抗侵蚀能力极显著提高(P0.05),1%~5%的FGDG可使土柱渗透性能提升近10倍,添加FGDG的各处理组间无显著差异(P0.05),1%FGDG对坡面径流量的最大削减率为37.5%,对土壤侵蚀(泥沙流失)的最大削减率为59.5%,有利于控制泥沙结合态磷的流失;3)各FGDG处理对土柱中总磷(total phosphorus,TP)流失的阻控率为23.6%~79.5%,且随着配比增加而上升,与对照组相比,1%FGDG对人工边坡土壤TP流失的阻控率为61.5%。土壤流失的TDP量占流失TP的比例只有0.6%~6.1%,反映出改善土壤渗透性能、削减地表径流冲刷是FGDG控制P流失的主要机制,而Ca与P之间的沉淀反应属于从属机制。     

Management options to decrease phosphorus and sediment losses from irrigated cropland grazed by cattle and sheep

In southern New Zealand, grazing of forage crops is common practice to satisfy feed requirements of animals in winter when pasture growth is limited. This practice has been shown to cause soil physical damage and increased loss of surface water contaminants sediment and phosphorus (P) to water bodies. Strategies to mitigate the loss of sediment and P were trialled on a Pallic soil type (Aeric Fragiaquept) in the North Otago Rolling Downlands of New Zealand. All sites were irrigated and measurements were made of losses in overland and sub‐surface flow from intensive cattle or sheep grazed, winter forage crops, and sheep grazed pasture. Two mitigations (restricted grazing of crop to three hours and the application of aluminium sulphate) were assessed for their potential to decrease contaminant loss from cropland. Volumes of surface runoff and loss of total P, filterable reactive P and sediment showed significant differences (P < 0.05) between the control treatments (i.e. no mitigation) with cattle crop (88 mm surface runoff) > sheep crop (67 mm) > sheep pasture (33 mm). The contribution of irrigation water to overland flow water, as a result of saturation‐excess conditions, varied between treatments with more loss under cattle crop (20% of total) compared with sheep crop (15%) and sheep pasture (11%). These differences are probably an effect of soil physical condition and highlight the importance of accurate irrigation scheduling to keep soil moisture below field capacity. Restricted winter grazing and alum application after grazing significantly (P < 0.05) decreased P losses in surface runoff under cattle (from 1.4 to 0.9 kg P/ha) and sheep (from 1.0 to 0.7 kg/P/ha) grazed crop plots by about 30%. In cattle grazed plots, restricted grazing also decreased suspended sediments (SS) by 60%. The use of restricted grazing is suggested as a means of decreasing P and SS loss from grazed winter forage crops. The use of alum shows some promise for decreasing P losses, but requires further work to determine its long‐term effectiveness and use in other soils and management regimes.     

灌溉水质与灌溉沟坡度对华北土壤径流和侵蚀的影响

Irrigation-induced soil erosion seriously affects the sustainability of irrigated agriculture. The effects of irrigation water quality and furrow gradient on runoff and soil loss were studied under simulated furrow irrigation in laboratory using a soil collected from an experimental station of China Agricultural University, North China. The experimental treatments were different combinations of irrigation water salt concentrations of 5, 10, 20, and 30 mmol_c L^-1, sodium adsorption ratios (SAR) of 0.5, 5.0, and 10.0 (mmol_c L^-1)^0.5, and furrow gradients of 1%, 3%, and 5%, with distilled water for irrigation at 3 furrow gradients as controls. The experimental data indicated that total runoff amount, sediment concentration in runoff, and total soil loss amount generally decreased with increasing salt concentration in irrigation water but increased with its sodicity and furrow gradient. The effects of water quality and furrow gradient on soil loss were greater than those on runoff, and the increase of furrow gradient decreased the influence of water quality on soil loss. When the salt concentration increased from 5 to 30 mmol_c L^-1 at SAR of 10.0 (mmol_c L^-1)^0.5, total runoff amount, sediment concentration, and total soil loss amount decreased by 3.89%, 52.1%, and 53.92%, and 10.57%, 38.86%, and 42.03% at the furrow gradients of 1% and 5%, respectively. However, they respectively increased by 3.37%, 45.34%, and 55.36%, and 3.86%, 10.77%, and 13.91% when SAR increased from 0.5 to 10.0 (mmol_c L^-1)^0.5 at the salt concentration of 5 mmol_c L^-1. Irrigation water quality and furrow gradient should be comprehensively considered in the planning and management of furrow irrigation practices to decrease soil loss and improve water utilization efficiency.     

再生水灌溉水平对土壤盐分累积与细菌群落组成的影响

为探明再生水不同灌水水平下土壤盐分、氮素、磷素与细菌群落组成动态变化效应,采用室内土柱灌水试验,研究再生水、自来水不同灌水水平对土壤盐分、氮素、磷素及细菌群落组成结构的影响。结果表明:1)再生水灌溉相比自来水显著提高了0~60 cm土层盐分含量、磷素及0~30 cm土层氮素含量也有所提高,降低了土壤细菌群落多样性和OTU数量;充分灌溉相比非充分灌溉提高了深层土壤盐分含量,降低了深层土壤细菌群落多样性和种类数。2)不同处理土壤细菌类群以放线菌门(24.5%~40.6%)和变形菌门(22.4%~30.3%)为主。非充分灌溉下,再生水灌溉相比自来水提高了土壤放线菌门、绿弯菌门、厚壁菌门及酸杆菌门比例,降低了变形菌门比例;充分灌溉下,再生水灌溉相比自来水大幅度提高了土壤放线菌门和硝化螺旋菌门比例,降低了土壤变形菌门、绿弯菌门、酸杆菌门及厚壁菌门比例。无论是在充分灌溉还是非充分灌溉下,再生水灌溉均对土壤放线菌门表现为促进作用,对变形菌门表现为抑制作用。再生水充分灌溉相比非充分灌溉对土壤放线菌门和变形菌门具有促进作用,对土壤绿弯菌门、酸杆菌门和厚壁菌门具有抑制作用;再生水灌水水平越高,越有利于土壤中优势菌群的生长。3)各处理土壤细菌代谢通路丰度占比最大的为膜转运、碳水化合物代谢及氨基酸代谢,再生水辅以较高灌水水平能够显著促进表层土壤微生物膜转运、碳水化合物代谢及氨基酸代谢过程。因此,再生水较高灌水水平可促进土壤物质能量循环,且对土壤细菌代谢繁殖过程也可起到积极的调节作用。研究可为再生水灌溉下的土壤生态环境效应研究提供依据。     

Relationship between Soil Phosphorus Availability and Phosphorus Loss Potential in Runoff and Drainage

Abstract

Elevated soil phosphorus (P) content is common in the central coastal valleys of California, the result of decades of the intensive vegetable production. Undesirably high P concentration in surface water in this region stimulated interest in evaluating techniques to rank the potential for soil P loss to the environment. Phosphorus availability of 25 representative soils from fields in vegetable rotations were evaluated by the following techniques: bicarbonate‐extractable P (P_bc)–calcium chloride, extractable P (P_cc), P extractable by iron‐impregnated paper (P_Fe), P extractable by anion exchange resin (P_ae), and the degree of P saturation (P_sat). A column study was conducted in which these soils were evaluated for soluble P concentration in runoff and leachate from two simulated irrigation events. There were strong correlations among all measures of soil P availability (r=0.66–0.90). Runoff soluble P was most strongly correlated with P_cc, P_ae, and P_bc (r=0.98, 0.93, and 0.91, or 0.98, 0.90, and 0.85 in the first and second irrigation, respectively). The relationship of runoff soluble P to P_bc, P_ae, and P_cc was characterized by a change point; runoff soluble P from soils <50 mg kg^?1 P_bc was minimal, whereas at higher P_bc runoff P reached levels of environmental concern. Leachate soluble P was also correlated with P_cc, P_ae, and P_bc (r=0.84–0.99). Across soils, leachate soluble P averaged 1.4 mg L^?1, compared to 0.11 mg L^?1 for runoff P. We conclude that P_cc, P_ae, and P_bc are useful tests to rank the potential for P loss in irrigation runoff or drainage. Given the relative complexity of the P_ae technique, P_bc and P_cc appear to be the most practical soil tests for this purpose.     

Evaluation of leaching and runoff losses of selenium from seleniferous soils through simulated rainfall

Experiments were conducted to study drainage and runoff losses of selenium (Se) from two seleniferous soils (from Simbly containing total Se 850 μg [kg soil]^–1 and from Barwa containing 1310 μg [kg soil]^–1) under simulated rainfall (250–260 mm in three rainstorms) conditions. Rainfall intensities ranged from 56 to 120 mm h^–1 with uniformity coefficients ranging from 70.6% to 84.2%. Selenium lost through drainage (sum of drainage from initially saturated soil for 24 h and through dry and wet runs) was 0.15% and 0.11% of total Se content in the two soils. In soils having similar pH and organic‐C content, losses of Se through drainage as well as runoff were defined by total Se, water‐soluble Se, CaCO₃ content, and texture of the soils. The amount of runoff water was almost two times in the soil with fine texture and less infiltration rate than in the other and that same trend was observed with respect to loss of sediment. The soil with higher CaCO₃ content and water‐soluble Se lost more Se with moving water both through leaching and runoff, whereas the other soil with fine texture lost greater amount of Se with the sediment. Total Se lost through drainage as well as runoff was 0.29% of the native Se present in both the soils suggesting that significant amount of Se could be lost from seleniferous soils during irrigation and rainfall events.     

Is Cadmium Loss in Surface Runoff Significant for Soil and Surface Water Quality: A Study of Flood-Irrigated Pastures?

Cadmium (Cd), a naturally occurring element, is a potentially biotoxic metal in terrestrial and aquatic ecosystems. Whether it is biotoxic or not will depend upon the concentration in the soil, its bioavailability and its potential transfer through the ecosystem. However, little data are available for losses to waterways, especially via surface runoff. A study was conducted on two long-term trials under pasture to determine how the concentration of Cd in the soil was affected by different irrigation and fertiliser regimes and in turn how this affected the potential for transfer in surface runoff and outwash of flood irrigation. Concentrations of total Cd in the soil varied from 0.06 to 0.58 mg kg^?1 and reflected different rates of P fertiliser applied (from 0 to 376 kg superphosphate ha^?1?year^?1), but was also less (20–25% compared to dryland) in treatments receiving more frequent irrigation when the same rate of P was applied. This indicated that there was potential for transfer. An experiment using simulated rainfall to generate surface runoff indicated that the major form of Cd lost was dissolved (on average 65% <0.45 μm) and could be predicted by water extraction of the soil. Loads of Cd in outwash were significant (0.17 to 0.92 g ha^?1?year^?1) and at least as great as the measured leaching losses in other studies. Loads confirmed the loss of Cd from each trial was largely dissolved, and related to soil water-extractable Cd and the frequency of irrigation. While Cd concentrations in sediment from ditches receiving outwash were enriched, indicating potential transfer to waterways, the effect will likely be small due to dilution and sorption by sediment and thereby localised to areas closer to the farm. However, to minimise any potential impact, management should be directed to minimising the occurrence of outwash (e.g. by better irrigation timing) or Cd transfer by using less Cd-rich P fertiliser or minimising P fertiliser use in areas susceptible to surface runoff.     

Measuring Water-Extractable Phosphorus in Manures to Predict Phosphorus Concentrations in Runoff

Water-extractable phosphorus (WEP) in manures can influence the risk of phosphorus (P) losses in runoff when manures are land applied. We evaluated several manure handling and extraction variables to develop an extraction procedure for WEP that will minimize pre-analysis manure-sample-handling effects on WEP measurements. We also related manure WEP determinations to runoff dissolved reactive phosphorus (DRP) concentrations found in previously conducted field simulated rainfall experiments using the same manures to evaluate WEP as a predictor of P runoff losses. Dairy and poultry manure WEP concentrations increased with manure-to-water extraction ratio and shaking time. Relative to fresh manures, drying and grinding dairy manures before analysis usually decreased WEP concentrations, while WEP in poultry manures was often increased. Pre-analysis handling effects on WEP were minimized at the 1:1000 extraction ratio with a 1-h shaking time. Relationships between manure WEP and runoff DRP concentrations were strongly influenced by season of year and WEP extraction procedure. The best prediction of DRP concentration in spring runoff experiments was with manure WEP concentration at the 1:1000 extraction ratio. With fall runoff studies, DRP concentrations were best predicted with WEP application rate rather than concentration. These seasonal differences can be explained by the greater percentage of rainfall that ran off in the fall compared to the spring. For all studies, runoff DRP concentrations were strongly related (r² = 0.82) to the ratio of runoff to rainfall volumes, confirming that models need to take runoff hydrology into account as well as manure WEP in P-loss risk assessments.