内蒙古河套灌区秋浇对不同类型农田土壤盐分淋失的影响

秋浇是河套灌区传统的秋后淋盐、春季保墒的一种特殊灌溉制度 ,秋浇对不同类型农田盐分损失影响的试验结果表明 ,秋浇前白菜地土壤含水率最高 ,向日葵地最低 ,秋浇后 5种农田土壤含水率均较高 ,且彼此间无显著性差异。秋浇后不同土壤剖面盐分的损失量按照表层 (0～ 40cm)、中层 (40～ 80cm)、深层 (80～ 1 2 0cm)依次递减(向日葵地除外 )。不同农田的盐分淋失量按照白菜地、向日葵地、玉米地、小麦 -玉米地、小麦地依次递减。非生长季灌溉下 ,农田土壤 0～ 1 0 0cm土层中盐分的淋失量与土壤储水量的增加量 (灌溉前土壤含水率 <2 50 g·kg- 1 ,r =0 .990 2 )密切相关 ,但与灌溉前土壤盐分初始含量无显著性关系     

A Forest Nutrient Cycling and Biomass Model (ForNBM) based on year-round,monthly weather conditions: Part II: Calibration,verification, and application

The ForNBM was applied to the Nashwaak Experimental Watershed Project in central New Brunswick, Canada. The data represented a mixed hardwood site and included information about nutrient leaching, foliage and wood biomass, leaf fall, and ancillary information required for model initialization. Ancillary information included forest cover type, stand density, forest floor depth, soil rooting depth, soil texture, soil substrate type, initial amounts of biomass and N, S, Ca, Mg, and K content in foliage, wood, and roots, and mineral soil nutrient contents in soil solution, on ion-exchange sites, and in the soil.The authors were able to calibrate the model with existing data. The model simulated observed monthly leaching reasonably well. The r²-values of model simulations compared with field observations of monthly leaching of NO₃⁻_N, NH₄⁺_N, Ca, Mg, and K were 0.78, 0.7, 0.78, 0.84, and 0.75, respectively. Modeled multi-year cumulative leaching of NO₃⁻_N, NH₄⁺_N, Ca, Mg, and K compared with actual values gave r²-values close to one for all cases considered.The results also showed that soil nutrient leaching had increased approximately five-fold for NO₃⁻_N, 80% for NH₄⁺_N, 71% for K, 20% for Ca, and 14% for Mg during the 3 years following a stem-only harvest operation applied watershed-wide. However, the model simulation showed that increased nutrient leaching during the 11 years following the stem-only harvest was small compared with the amounts removed in the biomass during the harvest. Increased nutrient leaching following harvesting did not appear to impact site productivity over the long term.     

Variation of salts and available nutrients in salt-affected soil during leaching process under the influence of organic ameliorators

ABSTRACT

This study investigated the potential influence of three organic ameliorators (peat, biochar and leonardite) on salts and nutrients in salt-affected soils during intermittent leaching. Results showed that nearly 90% of salt was removed from columns in the leaching process and sodium adsorption ratio (SAR) of the soil after leaching was reduced by 67.3% (control, CK), 62.9% (peat), 70.1% (biochar) and 55.0% (leonardite). Total N loss declined by 26.2% (peat), 11.7% (biochar) and 55.5% (leonardite) compared with CK in the process of leaching. The maintaining N (NH₄⁺ and NO₃^?) of soil after leaching was 8.25, 7.31, 11.31 and 14.48?mg/kg for CK, peat, biochar and leonardite treatments. Final P loss was 0.47, 0.31, 0.54, 0.27?mg/column in leaching for CK, peat, biochar and leonardite treatments. Soluble P of soil after leaching was measured as 6.95 (CK), 5.62 (peat), 8.52 (biochar) and 3.33 (leonardite) mg/kg. Leaching could remove the salt effectively but with nutrient loss in the process. The findings of this study suggest that organic ameliorators (biochar, peat or leonardite) play an important role in retaining nutrients during leaching as well as supplying nutrients after leaching to offer practical assistance for the amendment of salt-affected soil in the Yellow River Delta.     

Optimum Nitrogen Use and Reduced Nitrogen Loss for Production of Rice and Wheat in the Yangtse Delta Region

A long-term field and lysimeter experiment under different amount of fertilizer-N application was conducted to explore the optimal N application rates for a high productive rice–wheat system and less N leaching loss in the Yangtse Delta region. In this region excessive applications of N fertilizer for the rice–wheat production has resulted in reduced N recovery rates and environment pollution. Initial results of the field experiments showed that the optimal N application rate increased with the yield. On the two major paddy soils (Hydromorphic paddy soil and Gleyed paddy soil) of the region, the optimal N application rate was 225–270 kg N hm^–2 for rice and 180–225 kg N hm^–2 for wheat, separately. This has resulted in the highest number of effective ears and Spikelets per unit area, and hence high yield. Nitrogen leaching in the form of NO ₃ ^– -N occurs mainly in the wheat-growing season and in the ponding and seedling periods of the paddy field. Its concentration in the leachate increased with the N application rate in the lysimeter experiment. When the application rate reached 225 kg N hm^–2, the concentration rose to 5.4–21.3 mgN l^–1 in the leachate during the wheat-growing season. About 60% of the leachate samples determined contained NO ₃ ^– -N beyond the criterion (NO ₃ ^– -N 10 mg l^–1) for N pollution. In the field experiment, when the N application rate was in the range of 270–315 kg hm^–2, the NO ₃ ^– -N concentration in the leachate during the wheat-growing season ranged from 1.9 to 11.0 mg l^–1. About 20% of the leachate samples reached close to, and 10% exceeded, the criterion for N pollution. Long-term accumulation of NO ₃ ^– -N from leaching will no doubt constitute a potential risk of N contamination of the groundwater in the Yangtse Delta Region.     

Mechanisms of moisture stress in a mid-latitude temperate forest: Implications for feedforward and feedback controls from an irrigation experiment

While it is well established that stomata close during moisture stress, strong correlations among environmental (e.g., vapor pressure deficit, soil moisture, air temperature, radiation) and internal (e.g., leaf water potential, sap flow, root-shoot signaling) variables obscure the identification of causal mechanisms from field experiments. Models of stomatal control fitted to field data therefore suffer from ambiguous parameter identification, with multiple acceptable (i.e., nearly optimal) model structures emphasizing different moisture status indicators and different processes. In an effort to minimize these correlations and improve parameter and process identification, we conducted an irrigation experiment on red maples (Acer rubrum L.) at Harvard Forest (summers of 2005 and 2006). Control and irrigated trees experienced similar radiative and boundary layer forcings, but different soil moisture status, and thus presumably different diurnal cycles of internal leaf water potential. Measured soil moisture and atmospheric forcing were used to drive a transient tree hydraulic model that incorporated a Jarvis-type leaf conductance in a Penman–Monteith framework with a Cowan-type (resistance and capacitance) tree hydraulic representation. The leaf conductance model included dependence on both leaf matric potential, Ψ_L (so-called feedback control) and on vapor pressure deficit, D (so-called feedforward control). Model parameters were estimated by minimizing the error between predicted and measured sap flow. The whole-tree irrigation treatment had the effect of elevating measured transpiration during summer dry-downs, demonstrating the limiting effect that subsurface resistance may have on transpiration during these times of moisture stress. From the best fitted model, we infer that during dry downs, moisture stress manifests itself in an increase of soil resistance with a resulting decrease in Ψ_L, leading to both feedforward and feedback controls in the control trees, but only feedforward control for the irrigated set. Increases in the sum-of-squares error when individual model components were disabled allow us to reject the following three null hypotheses: (1) the f(D) stress is statistically insignificant (p = 0.01); (2) the f(Ψ_L) stress is statistically insignificant (p = 0.07); and (3) plant storage capacitance is independent of moisture status (p = 0.07).     

Laboratory weathering studies of coal refuse

Coal refuse samples from Staunton, Illinois, were continuously leached in soxhlet extractors at 97, 65, 55 and 45°C for up to 192 hr. An identical refuse sample was leached once a week for 11 weeks using a humidity cell at approximately 25°C. Leachate collected from the soxhlet and humidity cell apparatus was analysed for pH, EC, SO₄, Fe, Mn, Al and total acidity.The data indicate that concentrations of SO₄, Fe and Mn increased rapidly as the leaching temperature in the soxhlets increased. Soxhlet extractors removed virtually all soluble Fe and Mn species within 64 hr of leaching. A comparison of the leachate characteristics of the low-temperature soxhlet and humidity cell showed that the soxhlet removed 50% more total Fe and SO₄ for the complete leaching cycle. Pyrite oxidation in the soxhlet extractors was observed near the end of the extraction sequence, but pyrite oxidation in the humidity cell was masked by the release of soluble iron sulphates. Thus, the origin of leachate acidity in the humidity cell could not be distinguished between the soluble mineral phase and the acidity resulting from the oxidation of pyritie minerals.The results of this experiment suggests that the use of the soxhlet extractor for leaching coal refuse may produce a faster and more accurate representation of water quality impacts than would the use of the humidity cell. Long-term leaching studies must be completed to further clarify the role of both these leaching methods for predicting water quality impacts.Contribution of the Land Reclamation Program at Argonne National Laboratory, Argonne, Illinois 60439.     

碱性矿化水淋洗对土壤盐碱化及小麦生长的影响

为探讨不同矿化度的水对土壤盐渍化的影响及相应的淋洗分数,采用土柱模拟方法,以小麦为指示作物,设计1.0 g/L,1.5 g/L两种矿化度,按3750 m3/hm2灌溉量,分一水、二水两种灌次,秋后进行人工淡水淋洗。结果表明,在半干旱气候条件下,开发碱性矿化水灌溉矿化度不宜超过1.5 g/L,否则有引起碱化的危险。干旱期用碱性矿化水灌溉抗旱时,在同等灌水量的情况下,一水灌溉比二水灌溉积盐轻。各种人工淋洗处理比CK洗盐效果好,其中以等量淋洗综合效益最好。     

Modelling of leachates from dolomitic mine tailings

The REDEQL.EPAK computer model was used to study speciation of Pb, Cd, Zn, and Ca in leachates from dolomitic Pb mine tailings. By allowing or disallowing precipitation of solids and equilibration of the modelled leachate with atmospheric C0₂, comparison of fresh and aged leachates was made. The effects of treatment of the tailings with phosphate containing fertilizer were studied through addition of P0₄ ^3– to the modelled solution. Equilibrium constants pertaining to metal ion-humic acid complexation were added to the thermodynamic data base of the model in order to study the effects of decaying plant material on tailings leachate.Initial leachate of the tailings is found to be supersaturated with Cd and Zn. Non-complexed (free) Cd²⁺ and Zn²⁺ is predicted to comprise most of the soluble form of these metals in the leachate; Pb is predicted to be present largely as PbCO₃ ion pair. Equilibration of the leachate with the atmosphere is predicted to lead to extensive precipitation of CdCO₃ and ZnSiO₃. Precipitation of Pb₅(PO₄)₃Cl is predicted at high PO₄ ^3– concentration and at low pH. Complexation by the humic acid is predicted to compete effectively with other ligands in the leachate for the metal ions. The results are compared with experimental findings.     

Field Studies on 32P Movement and P Leaching from Flooded Paddy Soils in the Region of Taihu Lake, China

Field experiments were done in two sites, Yixing and Changshu, Jiangsu province, China, to study P movement and leaching in flooded paddy soils. P movement in soil was investigated by using the KH₂ ³²PO₄ tracker method, and the amount of P leached from the soil layer in different depths was estimated by measuring P concentrations in the soil solution and saturated hydraulic conductivities in field. Determination was done about one month after P application. There was 46% and 42% of total ³²P retained in the 0–5cm layer of soil in the Yixing site and in the Changshu site respectively. The ³²P retained in the 25–30 cm layer was only about 1–2% of the total ³²P added. Furthermore, 8.01% of ³²P in the soil of Yixing site and 16.8% of ³²P in the soil of Changshu site was lost from the layer 0–30cm soil. The seasonal amounts of P leached from the top soil layer and from bottom layer are about 4.5–5.8% and 1.6–2.1% of the total P application, respectively. Changes of total P concentrations in soil solutions during rice growth showed that the fertilizer P applied before flooding of the paddy fields suffered a flash leaching loss and a slow leaching loss. We concluded that the fertilizer P could quickly move in the flooded paddy rice field and parts of it can enter into surface water and ground water. Unless the P application is well managed the risk of P loss and consequently environmental pollution exist.     

垃圾填埋场渗滤液灌溉地土壤和植物中重金属积累

分加在广州市李坑垃圾填埋场有渗滤液回灌的地表和未经渗滤液回灌的地表随机采集土样,深度达１ｍ,同时分别采集长于灌溉地和非灌溉地上的三个优势植物种（牛筋草,孔雀稗和狗牙根）为代表,调查渗滤液灌溉后封和植物的重金属（Ｃｕ,Ｚｎ,Ｐｂ,Ｃｄ）积累效应。结果表明,渗滤液灌溉地的不同深度土壤和地表植物体内都有不同程度重金属积累。经ｔ－检验,Ｃｕ,Ｐｂ和Ｃｄ在所调查的各土层内的积累效应α＝０．０５时都达到显著水     

Assessing the effect of long-term crop cultivation on distribution of Cd in the root zone

Trace elements such as cadmium (Cd) may be inadvertently added to cropland soils through application of fertilizers, irrigation water, and other amendments. These toxic trace elements pose a potentially threat to soil quality and, through the food chain transfer, to human health. A generalized soil trace element mass balance model that accounts for the interactive processes governing the reactions of trace elements in soils, and consequently removed with crop harvest and leaching out of the soil profile with irrigation water was developed in this research. The model conceptually approximates the mechanisms and kinetics of a real field cropland system. The model was used to evaluate the long-term cultivation on distribution of Cd in California croplands. Under typical California cropping practices, Cd added into the soils accumulated primarily in the plow layer while the Cd content below the plow layer was barely affected. After 100 years of continuous cultivation, the soil Cd content of the plow layer increases from the background level 0.22 mg kg⁻¹ to 0.40 mg kg⁻¹. The accumulation of Cd in the plow layer is in proportion to the external inputs and is affected by the soil and plant characteristics, and management practices. The model can be used to evaluate the environmental fates of other toxic element in soils with case specific parameters.     

Leaching characteristics of heavy metals during cement stabilization of fly ash from municipal solid waste incinerators

The leaching characteristics of heavy metals in products of cement stabilization of fly ash from a municipal solid waste incinerator were investigated in this paper. The stabilization of heavy metals such as Cd, Pb, Cu, and Zn in fly ash from such incinerators was examined through the national standard method in China based on the following factors: additive quantity of cement and Na₂S, curing time, and pH of leaching liquor. The results showed that as more additives were used, less heavy metals were leached except for Pb, which is sensitive to pH of the leachate, and the worse effect was observed for Cd. The mass ratio of cement to fly ash = 10% is the most appropriate parameter according to the national standard method. When the hydration of cement was basically finished, stabilization of heavy metals did not vary after curing for 1 d. The mixtures of cement and fly ash had excellent adaptability to environmental pH. The pH of leachate was maintained at 7 when pH of leaching liquor varied from 3 to 11.     

Hydraulic properties of typical salt-affected soils in Jiangsu Province, China

Every year about 1,500 ha of land is reclaimed from the sea along the coastline of Jiangsu Province, China. It is important to characterize the hydraulic properties of this reclaimed land to be able to predict and manage salt and water movement for amelioration of these saline soils. In this paper, we report hydraulic properties of these salt-affected soils. The pressure-plate method, constant head method, the crust method and Klute's method were used in this study. The saturated hydraulic conductivities of the soils ranged from 128.66 to 141.26 cm/day and decreased with increasing soil depth. The unsaturated hydraulic conductivities followed an exponential function of pressure head. The soil water retention curves were similar for three soil layers in the soil. The saturated water content, field capacity and wilting point decreased with increasing soil depth. Plant available water contents of the three layers in the soil profile were 0.21, 0.20 and 0.19 cm³/cm³, respectively. The unsaturated soil water diffusivity of the studied soils ranged from 0.07 to 10.46 cm²/min, and was related to the water content via an exponential relationship.     

Estimating soil salinity in different landscapes of the Yellow River Delta through Landsat OLI/TIRS and ETM+ Data

Soil salinization has increasingly become a serious issue in coastal zone due to global climate changes and human disturbances. Assessment of soil salinity, especially at the landscape scale, is critical to coastal management and restoration. Two data from OLI/TIRS and ETM+ sensors of Landsat satellite were used to compare their ability to invert the spatial pattern of soil salinity in both farmland and salt marsh landscapes in the Yellow River Delta, China, respectively. The results showed that the in situ electrical conductivity (EC _a ) of soil, representing soil salinity, were closely related with spectral parameters and salinity indices calculated by the remote sensing data. The results of multiple regression models have showed that nearly all the spectral parameters and salinity indices calculated by OLI/TRIS data were more sensitive to soil salinity than those by ETM+ data. Therefore, the models based on OLI/TIRS data are superior to those on ETM+ data in estimating the spatial pattern of soil salinity in farmland and salt marsh landscapes. Our results were very helpful to evaluate the levels of soil salinization in the Yellow River Delta.     

Modeling compensated root water and nutrient uptake

Plant root water and nutrient uptake is one of the most important processes in subsurface unsaturated flow and transport modeling, as root uptake controls actual plant evapotranspiration, water recharge and nutrient leaching to the groundwater, and exerts a major influence on predictions of global climate models. In general, unsaturated models describe root uptake relatively simple. For example, root water uptake is mostly uncompensated and nutrient uptake is simulated assuming that all uptake is passive, through the water uptake pathway only. We present a new compensated root water and nutrient uptake model, implemented in HYDRUS. The so-called root adaptability factor represents a threshold value above which reduced root water or nutrient uptake in water- or nutrient-stressed parts of the root zone is fully compensated for by increased uptake in other soil regions that are less stressed. Using a critical value of the water stress index, water uptake compensation is proportional to the water stress response function. Total root nutrient uptake is determined from the total of active and passive nutrient uptake. The partitioning between passive and active uptake is controlled by the a priori defined concentration value c_max. Passive nutrient uptake is simulated by multiplying root water uptake with the dissolved nutrient concentration, for soil solution concentration values below c_max. Passive nutrient uptake is thus zero when c_max is equal to zero. As the active nutrient uptake is obtained from the difference between plant nutrient demand and passive nutrient uptake (using Michaelis–Menten kinetics), the presented model thus implies that reduced passive nutrient uptake is compensated for by active nutrient uptake. In addition, the proposed root uptake model includes compensation for active nutrient uptake, in a similar way as used for root water uptake. The proposed root water and nutrient uptake model is demonstrated by several hypothetical examples, for plants supplied by water due to capillary rise from groundwater and surface drip irrigation.     

Adsorption of pesticides by salorthids and camborthids of Punjab,Pakistan

This study was conducted to examine adsorption of pesticides bifenthrin, carbosulfan, λ-cyhalothrin, cypermethrin, endosulfan, parathion methyl, monocrotophos and 4-nitrophenol by sandy clay loam (S.C.L) and sandy loam (S.L) soils (with varying organic content). There was no significant difference between the observed soil water partitioning coefficient values (K _d) derived from linear and nonlinear Freundlich isotherms. Adsorption of pesticides on S.C.L soils was higher than those on S.L soils. K _d values showed significant correlations (r ²?=?0.8???0.99 and 0.65???0.97) with soil organic carbon content (OC) and weak correlations (r ²?=?0.2???0.29 and 0.1???0.18) with clay contents of S.C.L and S.L soil at p?≤?0.05, respectively for all pesticides (except monocrotophos). Observed K _oc values (soil-water partitioning constants based on the organic C fraction of the soil) were in accordance with the literature values of Wauchope and Tomlin with a maximum deviation of less than 0.5 log units. Ten Quantitative Property-Property Relationships (QPPR) among water solubility, n-octanol water coefficient (K _ow) and K _oc were proposed for studied pesticides except monocrotophos. The models were considered acceptable when predicted-observed difference for log?K _ow and log?K _oc were ≤?0.3 and ≤?0.5?log units, respectively, during the validation procedure. This work indicates that the log?K _oc derived from the log K_ow, from some of existing relationships, may be a fair predictor where observed values (i.e., K _d and K _oc) are not available. Furthermore, predicted leaching potential by groundwater ubiquity scores (GUS) equation was solved by using observed K _oc values and literature reported half lives of pesticides. GUS ranked the mobility of nonvolatile compounds i.e., bifenthrin, λ-cyhalothrin, cypermethrin and endosulfan extremely low; methyl parathion very low; 4-nitrophenol low; carbofuran and monocrotophos very high in S.C.L and S.L soils, respectively. Results discussed in this paper provide background to prioritize pesticides or chemical groups that should be evaluated under field conditions with regard to their leaching potential to groundwater in arid climates.     

A Comparison of the Short-Term Dynamics of Soil “Damage” Due to Enhanced Nitrogen Deposition As Ammonium Sulphate Or Nitric Acid

An experiment has been conducted to contrast the effects of enhanced oxidised and reduced nitrogen deposition upon key chemical parameters in a Calluna moorland podzol. A 40 cm deep podzol profile, derived from granite, was reconstructed in one hundred 4.2 cm diameter cores. for 20 weeks, the cores were subjected twice weekly to simulated rainfall containing either twice ambient nitrogen deposition in Aberdeen, or further enhanced nitrogen (further 2- and 6-fold increases) as nitric acid or ammonium sulphate. to quantify the dynamics of soil change in each horizon, randomly selected cores were destructively analysed every two weeks and the soils analysed. Increased nitrogen inputs, regardless of form, substantially and immediately reduced surface soil pH_water via the mobile anion or salt effect. for the higher nitrogen treatments, the pH reduction was seen throughout the profile. Longer term soil acidification was also seen in the pH_{calcium chloride} results over the 20 weeks. at a given nitrogen deposition rate, the effects of ammonium sulphate and nitric acid on soil pH_{calcium chloride} were similar. the ammonium sulphate treatments were especially effective at reducing base saturation throughout much of the profile, the direct base cation leaching being associated with substantial ammonium accumulation. the results suggest that the direct base cation leaching caused by ammonium deposition needs to be considered when assessing atmospheric pollution “damage” to heathland soils.     

Effect of biochar addition on short-term N<Subscript>2</Subscript>O and CO<Subscript>2</Subscript> emissions during repeated drying and wetting of an anthropogenic alluvial soil

Agricultural soils are an important source of greenhouse gases (GHG). Biochar application to such soils has the potential of mitigating global anthropogenic GHG emissions. Under irrigation, the topsoils in arid regions experience repeated drying and wetting during the crop growing season. Biochar incorporation into these soils would change the soil microbial environment and hence affect GHG emissions. Little information, however, is available regarding the effect of biochar addition on carbon dioxide (CO₂) and nitrous oxide (N₂O) emissions from agricultural soils undergoing repeated drying and wetting. Here, we report the results of a 49-day aerobic incubation experiment, incorporating biochar into an anthropogenic alluvial soil in an arid region of Xinjiang Province, China, and measuring CO₂ and N₂O emissions. Under both drying–wetting and constantly moist conditions, biochar amendment significantly increased cumulative CO₂ emission. At the same time, there was a significant reduction (up to ~20 %) in cumulative N₂O emission, indicating that the addition of biochar to irrigated agricultural soils may effectively slow down global warming in arid regions of China.     

涕灭威农药污染地下水的影响因子分析

农药在土壤中的淋溶受许多因子的影响与制约。本文根据农药在土壤中的环境行为，建立了农药土壤残留动态与淋溶归宿的计算机模型，并用此模型计算了模拟各种不同环境条件下涕灭威农药在土层中的淋溶情况。结果表明：农药的使用量、土层中农药的降解半衰期、施药地区土壤的质地、降水或灌溉水量及其距施药后的时间对涕灭威在土层中的淋溶有较大的影响，而土壤有机碳含量则影响不大；地下水埋深对农药地下水污染的影响颇大。地下水埋深不足１ｍ的地区，极易受农药的污染。