Evaluation of the root zone water quality model for predicting water and NO3–N movement in an Iowa soil

Evaluation of computer models with field data is required before they can be effectively used for predicting agricultural management systems. A study was conducted to evaluate tillage effects on the movement of water and nitrate–nitrogen (NO₃–N) in the root zone under continuous corn (Zea mays L.) production. Four tillage treatments considered were: chisel plow (CP), moldboard plow (MP), no-tillage (NT), and ridge-tillage (RT). The root zone water quality model (RZWQM: V.3.25) was used to conduct these simulations. Three years (1990–1992) of field observed data on soil water contents and NO₃–N concentrations in the soil profile were used to evaluate the performance of the model. The RZWQM usually predicted higher soil water contents compared with the observed soil water contents. The model predicted higher NO₃–N concentrations in the soil profile for MP and NT treatments in comparison with CP and RT treatments, but the magnitude of simulated NO₃–N peak concentrations in the soil profile were substantially different from those of the observed peaks. The average NO₃–N concentrations for the entire soil profile predicted by the model were close to the observed concentrations except for ridge tillage (percent difference for CP=+5.1%, MP=+12.8%, NT=+18.4%, RT=−44.8%). Discrepancies between the simulated and observed water contents and NO₃–N concentrations in the soil profile indicated a need for the calibration of plant growth component of the model further for different soil and climatic conditions to improve the N-uptake predictions of the RZWQM.     

Effect of Soil Phosphorus Levels on Phosphorus Runoff Concentrations from Turfgrass

Phosphorus (P) loss from urban areas has been identified as a major contributor to declining surface water quality. The objective of this study was to determine the relationship between extractable soil P, depth of soil sampling, and dissolved reactive P (DP) concentration in runoff from turfgrass areas. At each site, runoff was generated on turfgrass and adjoining areas where turfgrass cover was removed. Across all six locations and the wide range of nutrient management schemes, variation of extractable soil P concentration and saturation ratios of 0–2cm samples accounted for 49–59% (r ² = 0.49–0.59, n = 92) of variation of DP concentration in runoff from bare soil and soil with turfgrass cover. Despite a high degree of soil P stratification, changing sampling depth generally did not improve the relationship between soil test P and runoff DP concentrations. Across the narrower range of soil P levels common to lawns in New York (0–50mg kg^?1 Morgan extractable soil P), none of the soil tests or P saturation levels (for 0–2cm depth) could accurately predict runoff P concentrations from soil with turfgrass cover (r ² = 0.02 to 0.23, n = 72). For bare soil plots, restricting the analysis to the same range (<50mg kg^?1 Morgan extractable P) did not alter the relationship between soil test P and runoff DP concentrations observed for the entire range (0–658mg kg^?1) of soil-test P concentrations. These results suggest soil testing will not be an effective tool to predict runoff from turfgrass areas across the range of soil P levels common to New York State.     

RZWQM2模型模拟牛场肥水施用夏玉米土壤硝态氮迁移特征

为研究华北平原种养结合中养殖肥水的合理施用,减少典型农田水肥施用后土壤氮淋溶对地下水的影响。该研究以河北省徐水区夏玉米为研究对象,应用RZWQM2模型验证牛场肥水施用玉米农田的可行性,对2014—2016年玉米种植前后数据进行模型参数率定与验证。验证结果表明,土壤体积含水率的均方根误差和平均相对误差值分别在0.000 6～0.070 7 cm~3/cm~3和0.21%～21.44%之间变化,土壤硝态氮均方根误差和平均相对误差值分别在0.000 8～2.617 3 mg/kg和0.03%～18.58%之间变化,其中牛场肥水施用土壤中硝态氮主要在0～120 cm土层发生变化,说明RZWQM2模型可以用来模拟华北平原牛场肥水施用对土壤水分、硝态氮含量及玉米产量的动态变化。利用率定和验证后的模型进行了夏玉米农田硝态氮淋溶的验证与预测,表明硝态氮淋溶浓度随肥水氮量的增加而增加。RZWQM2模型可以应用于牛场肥水施用农田的模拟,为预测和评估土壤适宜的肥水施用提供更合适的方法。     

Mobility and dissipation of ethofumesate and halofenozide in turfgrass and bare soil.

The effect of turfgrass cover on the leaching and dissipation of ethofumesate and halofenozide was studied. Sampling cylinders (20 cm diam. x 30 cm long) were placed vertically in plots of creeping bentgrass (Agrostis palustris Huds.), tall fescue (Festuca arundinaceae Schreb.), or bare soil. ethofumesate [(+/-)-2-ethoxy-2,3-dihydro-3,3-dimethylbenzofuran-5-yl methansulfonate] was applied at 840 g ai ha(-)(1) on September 21, 1997. Halofenozide (N-4-chlorobenzoyl-N'-benzoyl-N'-tert-butylhydrazine) was applied at 1680 g ai ha(-)(1) on August 30, 1998. Replicate sampling cylinders were removed 2 h after treatment and 4, 8, 16, 32, and 64 days after treatment. Sampling cylinders were sectioned by depths and soil extracts were assayed by HPLC with a pesticide detection limit of 0.01 mg kg(-)(1). Turfgrass was divided into verdure and thatch and analyzed separately. ethofumesate leaching in turfgrass was reduced by at least 95% compared to leaching in bare soil. The half-life of ethofumesate in bare soil was 51 days compared to 3 days in turfgrass. Halofenozide showed similar leaching with or without turfgrass. Fifty percent dissipation of halofenozide did not occur within 64 days, regardless of organic matter cover.     

RZWQM模拟小麦 玉米轮作系统氮素运移及损失特征

本文以位于华北平原的河北省农林科学院大河试验站冬小麦-夏玉米轮作系统为研究对象,应用RZWQM(Root Zone Water Quality Model)模型对华北地区2010年冬小麦-夏玉米的1个轮作周期内土壤剖面水分和剖面硝态氮累积、作物产量、硝态氮淋失以及氨挥发进行模型模拟。本文利用并通过RZWQM模型在不同梯度施肥情况下讨论了施肥量对小麦-玉米轮作体系中硝态氮淋溶和氨挥发特性,并尝试通过拟合出的回归曲线来确定施氮量和硝态氮淋失和氨挥发之间的关系。设置冬小麦-夏玉米轮作周期施纯氮量分别为575 kg-hm-2(N3)、400 kg-hm-2(N2)、215 kg-hm-2(N1)和0 kg-hm-2(N0)4个处理,应用轮作周期中玉米数据进行模型参数率定,应用小麦进行模型参数的验证。结果表明:模型的玉米率定以及小麦验证的过程中结果偏差均在可接受范围内,剖面水分率定均方误差(RMSE)最高为0.019 cm3-cm-3,平均相对误差(MRE)最高为15.98%;剖面硝态氮累积验证结果 RMSE平均值为4.580 mg-kg-1,MRE平均值为52.63%。在模型验证的小麦-玉米季土壤基础上,硝态氮淋溶和氮挥发都与施氮量呈一定线性相关关系。综上结论,本试验结果能较好地模拟华北地区土壤剖面水分、硝态氮积累,以及施氮量对土壤硝态氮淋失和氨挥发的影响,为预测和估算土壤适宜施氮量提供了便捷可靠的方法。但RZWQM模型验证参数过程还需要进一步的校正与完善。     

RZWQM simulated effects of crop rotation, tillage, and controlled drainage on crop yield and nitrate-N loss in drain flow

Accurate simulation of agricultural management effects on N loss in tile drainage is vitally important for understanding hypoxia in the Gulf of Mexico. An experimental study was initiated in 1978 at Nashua, Iowa of the USA to study long-term effects of tillage, crop rotation, and N management practices on subsurface drainage flow and associated N losses. The Root Zone Water Quality Model (RZWQM) was applied to evaluate various management effects in several previous studies. In this study, the simulation results were further analyzed for management effects (tillage, crop rotation, and controlled drainage) on crop production and N loss in drain flow. RZWQM simulated the observed increase in N concentration in drain flow with increasing tillage intensity from NT (no-till) to RT (ridge till) to CP (chisel plow) and to MP (moldboard plow). It also adequately simulated tillage effects on yearly drain flow and yearly N loss in drain flow. However, the model failed to simulate lower corn and soybean yields under NT than under MP, CP, and RT. On the other hand, RZWQM adequately simulated lower yearly drain flow and lower flow-weighted N concentration in drain flow under CS (corn-soybean) and SC (soybean-corn) than under CC (continuous corn). The model adequately simulated higher corn yield under CS and SC than under CC. Applying the newly suggested N management practice for the Midwest of controlled drainage, the model simulated a 30% reduction in drain flow and a 29% decrease in N losses in drain flow under controlled drainage (CD) compared to free drainage (FD). With most of the simulations in reasonably close agreement with observations, we concluded that RZWQM is a promising tool for quantifying the relative effects of tillage, crop rotation, and controlled drainage on N loss in drainage flow. Further improvements on simulated management effects on crop yield and N mineralization are needed, however.     

Predicting regional emissions and near-field air concentrations of soil fumigants using modest numerical algorithms: a case study using 1,3-dichloropropene

Soil fumigants, used to control nematodes and crop disease, can volatilize from the soil application zone and into the atmosphere to create the potential for human inhalation exposure. An objective for this work is to illustrate the ability of simple numerical models to correctly predict pesticide volatilization rates from agricultural fields and to expand emission predictions to nearby air concentrations for use in the exposure component of a risk assessment. This work focuses on a numerical system using two U.S. EPA models (PRZM3 and ISCST3) to predict regional volatilization and nearby air concentrations for the soil fumigant 1,3-dichloropropene. New approaches deal with links to regional databases, seamless coupling of emission and dispersion models, incorporation of Monte Carlo sampling techniques to account for parametric uncertainty, and model input sensitivity analysis. Predicted volatility flux profiles of 1,3-dichloropropene (1,3-D) from soil for tarped and untarped fields were compared against field data and used as source terms for ISCST3. PRZM3 can successfully estimate correct order of magnitude regional soil volatilization losses of 1,3-D when representative regional input parameters are used (soil, weather, chemical, and management practices). Estimated 1,3-D emission losses and resulting air concentrations were investigated for five geographically diverse regions. Air concentrations (15-day averages) are compared with the current U.S. EPA's criteria for human exposure and risk assessment to determine appropriate setback distances from treated fields. Sensitive input parameters for volatility losses were functions of the region being simulated.     

Evaluation of Mobility and Dissipation of Mefenoxam and Pendimethalin by Application of CSTR Model and Field Experiments Using Bare and Tobacco Tilled Soil Columns

The soil mobility and dissipation of two pesticides with different physicochemical properties, namely mefenoxam, a systemic fungicide, and pendimethalin a selective herbicide, were determined in bare and tobacco tilled soil columns, which were installed in field conditions for over 125 days. Soil samples were collected at specific time intervals for a 125-day period and the rate of pesticide dissipation and leaching through the soil column was studied. The dissipation half-lives of mefenoxam from the top soil layer in tilled and bare soil columns were estimated at 10.3 and 13.1 days, respectively, while the corresponding half-lives for pendimethalin were 26.7 and 27.5 days, respectively. The dissipation of mefenoxam and pendimethalin from the top soil in tobacco cultivation was faster in comparison with bare soil; however, 120 days after their application, both pesticide residues were detected in the soil. Maximum concentrations of mefenoxam and pendimethalin were observed on the 15^th and 33^rd day, respectively, in the soil layer of 5–10 cm depth and on the 30^th day and 63^rd day, respectively, in the soil layer of 10–15 cm depth. Higher concentrations were observed in bare soil columns. The leaching of both pesticides was simulated with the continuous stirred tank reactor (CSTR) in series model. The simulated peak concentration and peak time for both pesticides fitted reasonably well to the experimental values.     

Surface control of desert pavement pedologic process and landscape function,Cima Volcanic field,Mojave Desert,California

Desert pavement is a distinctive feature widespread across arid lands of the world. It plays a dynamic role in geomorphic, hydrologic, and ecologic processes. Where desert pavement predominates, infiltration is limited and rainfall is delivered as runoff to nearby bare ground areas where shrubs cluster. Desert pavement surfaces may appear monotonously flat and barren, but we have found, instead, that they are a complex association of landscape and hydrologic elements governed by their surface characteristics. Previously, we identified six unique surface mosaic types that accurately capture the subtle, but distinct, variations in surface clast arrangements for a desert pavement landscape formed on a single-aged basalt flow in the Mojave Desert. We now report that these surface mosaics predict the spatial distribution of fundamental desert vegetation and soil characteristics. Characteristics of soil morphology and texture, the leaching depth of soluble salts, percent plant cover, and shrub species diversity are remarkably consistent for each mosaic type across a 580,000-year-old basalt flow even when measured >1 km apart. Hydrologic character is distinctly different between desert pavement and bare ground regions and vegetation distributions reflect the spatially heterogeneous soil moisture. Where desert shrubs cluster on the three bare ground surface mosaics, leaching is deep, removing most soluble salts to below the 50-cm depth. Where shrubs are absent or few, on the three desert pavement mosaics, leaching depths are shallow, with soluble salt depth distributions as well as desert shrub percent cover precisely controlled by the percent clast cover of the surface.     

内蒙古杭锦旗北部盐碱田温湿盐动态与生产利用

为探析水-热-盐关系以及植被对盐碱田改良的意义,利用2008年8月2日-8月6日在内蒙古杭锦旗黄河灌区盐碱田进行的试验观测数据,主要通过方差分析与典型相关分析方法对3个样地(裸地、紫花苜蓿地和玉米地)土壤温度(0-30cm土层)、湿度(0-20cm土层)、盐度(0-100cm土层)的动态变化进行了分析。结果表明,3个样地的温(度)-湿(度)-盐(度)动态基本呈现裸地苜蓿地玉米地的格局;0-5cm地温与耕作层(0-20cm)的土壤水分具有显著相关关系,是0-30cm土层内地温驱动水盐动态的主要热力因子;植物能够减少土壤表层积盐,并可以降低碱化度;苜蓿地比玉米地具有更低的钠吸附比值。在盐碱地区选择耐盐碱牧草品种开展草田轮作,有益于盐碱土壤的改良与利用。     

秸秆和植被覆盖对江苏滨海盐土土壤盐分变化的影响

研究秸秆覆盖和植被(田菁)覆盖条件下滨海盐土土壤水盐的动态变化规律,为沿海滩涂盐碱地脱盐改良提供依据。本研究以含盐量6.98 g·kg~(-1)的滨海盐土为研究对象,设置秸秆覆盖和种植田菁2种覆盖处理,以裸地为对照,研究不同覆盖处理对滨海盐土土壤含水量和土壤盐分动态变化的影响。结果表明:秸秆覆盖下的土壤含水量(27.58%)显著高于田菁覆盖(26.70%)和裸地(26.61%),后两者差异未达显著水平。处理1年后0~20、20~40 cm土层的秸秆覆盖、田菁覆盖和裸地不同处理间土壤含盐量的差异均达显著或极显著水平;秸秆覆盖处理的脱盐率为田菁覆盖处理的2倍。回归分析表明裸地和田菁覆盖下土壤盐分含量与累积降雨量的关系可用二次多项式拟合,田菁覆盖下的淋洗方程(EC_a/EC_i与D_w/D_s间的关系)可用三次多项式拟合;而秸秆覆盖条件下土壤盐分含量与累积降雨量的关系、淋洗方程均表现为指数函数关系y=ae~(bx)(P0.01)。秸秆覆盖条件下滨海滩涂0~40 cm土层脱盐80%需要386.8 mm的累积降雨量。结果表明秸秆和植被覆盖技术在江苏滨海盐土可获得较好的脱盐效果,具有较好的应用前景。     

Simulated N management effects on corn yield and tile-drainage nitrate loss

Thoroughly tested simulation models are needed to help quantify the long-term effects of agriculture. We evaluated the Root Zone Water Quality Model (RZWQM) response to different N management strategies and then used the tested model with observed weather data from 1961-2003 to quantify long-term effects on corn (Zea mays L.) yield and flow weighted nitrate-N concentration in subsurface “tile” drainage water (Nconc). Fourteen years (1990-2003) of field data from 30, 0.4 ha plots in northeast Iowa were available for model testing. Annual crop yield, nitrate-N loss to subsurface “tile” drainage water (Nloss), Nconc, and subsurface “tile” drainage amount (drain) for various management scenarios were averaged over plots and years to create five chemical fertilizer and five swine manure treatments. Predicted corn yield and Nconc for the 10 treatments were significantly correlated with observed data (R² > 0.83). The Root Mean Square Errors (RMSE) were 15% and 18% of its observed average Nconc for chemical fertilizer and manure treatments, respectively. Corresponding RMSEs for corn yields were 8% and 10% of its observed average corn yields for chemical fertilizer and manure treatments. The long-term simulations indicate that average corn yield plateaus and Nloss accelerates as quadratic functions of increasing spring UAN-N rates from 100 to 200 kg N/ha. Winter wheat (Triticum aestivum L.) sowed after corn and soybean [Glycine max (L.) Merr.] harvest was predicted to reduce long-term Nloss by 5 to 6 kg N/ha, which appears consistent with published field studies and may be a treatment to ameliorate agricultural management with potential for elevated Nloss such as swine manure application to soybean. The results suggest that after calibration and thorough testing, RZWQM can be used to quantify the relative effects of corn production and Nconc under several alternative management practices.     

Soil microbial biomass and nitrogen dynamics in a turfgrass chronosequence: A short-term response to turfgrass clipping addition

A mechanistic understanding of soil microbial biomass and N dynamics following turfgrass clipping addition is central to understanding turfgrass ecology. New leaves represent a strong sink for soil and fertilizer N, and when mowed, a significant addition to soil organic N. Understanding the mineralization dynamics of clipping N should help in developing strategies to minimize N losses via leaching and denitrification. We characterized soil microbial biomass and N mineralization and immobilization turnover in response to clipping addition in a turfgrass chronosequence (i.e. 3, 8, 25, and 97 yr old) and the adjacent native pines. Our objectives were (1) to evaluate the impacts of indigenous soil and microbial attributes associated with turf age and land use on the early phase decomposition of turfgrass clippings and (2) to estimate mineralization dynamics of turfgrass clippings and subsequent effects on N mineralization of indigenous soils. We conducted a 28-d laboratory incubation to determine short-term dynamics of soil microbial biomass, C decomposition, N mineralization and nitrification after soil incorporation of turfgrass clippings. Gross rates of N mineralization and immobilization were estimated with ¹⁵N using a numerical model, FLAUZ. Turfgrass clippings decomposed rapidly; decomposition and mineralization equivalent to 20-30% of clipping C and N, respectively, occurred during the incubation. Turfgrass age had little effect on decomposition and net N mineralization. However, the response of potential nitrification to clipping addition was age dependent. In young turfgrass systems having low rates, potential nitrification increased significantly with clipping addition. In contrast, old turfgrass systems having high initial rates of potential nitrification were unaffected by clipping addition. Isotope ¹⁵N modeling showed that gross N mineralization following clipping addition was not affected by turf age but differed between turfgrass and the adjacent native pines. The flush of mineralized N following clipping addition was derived predominantly from the clippings rather than soil organic N. Our data indicate that the response of soil microbial biomass and N mineralization and immobilization to clipping addition was essentially independent of indigenous soil and microbial attributes. Further, increases in microbial biomass and activity following clipping addition did not stimulate the mineralization of indigenous soil organic N.     

Simulating leaf area of corn plants at contrasting water status

An exponential decay function was fitted with literature data to describe the decrease in corn leaf expansion rate as predawn leaf water potential decreases. The fitted function was then applied to modify an existing leaf area simulation module in a soil–plant–atmosphere continuum corn simulation model (MaizSim) in order to simulate leaf area of corn plants at different water status. Data were collected from field for two years as well as from sunlit growth chambers located at USDA-ARS facilities in Beltsville, MD with different irrigation frequencies. Comparison among simulations and measurements indicated that the modified leaf area module improved leaf area simulation for corn plant under different drought stress. For plants under more severe drought stress, the improvement in leaf area simulation was more significant. These results suggested that the modified leaf area model presented an approach to mechanistically link corn leaf area with corn plant water status, and was suitable for integration with existing corn models that simulate corn leaf area.     

冻融期灌水和覆盖对南疆棉田水热盐的影响

为了探索不同冬灌定额和地表覆盖模式对棉田水热盐的影响,该文设置了冬灌裸地(winter irrigation with bare land,WIB)、冬灌留秆(winter irrigation with high cotton stubble,WICS)、冬灌玉米秸秆覆盖(winter irrigation with corn straw mulching,WICM)、免冬灌裸地(no winter irrigation with bare land,NWIB)、免冬灌留秆(no winter irrigation with high cotton stubble,NWICS)和免冬灌玉米秸秆覆盖(no winter irrigation with corn straw mulching,NWICM)6个处理。经过2013-11-15-2014-04-04和2014-11-15-2015-04-04冬季大田试验,得到:灌水和地表覆盖可以平抑土壤温度的变幅,免冬灌或冬灌条件下,温度变异幅度均为裸地留秆玉米秸秆覆盖。玉米秸秆覆盖更有利于土壤水分保持,WICM土壤储水量比WIB和WICS分别多29.10%和10.36%,NWICM土壤储水量比NWIB和NWICS分别多14.97%和2.21%,经过两年冻融过程NWIB、NWICS和NWICM 0~100 cm土壤储水量平均减少了18.32、7.36和2.62 mm。(免)冬灌0~30 cm土壤含盐量均为裸地留秆玉米秸秆覆盖;0~100 cm土壤范围冬灌盐分淋洗率为玉米秸秆覆盖(34.86%)留秆(15.82%)裸地(7.26%);免冬灌0~100cm积盐率为裸地(10.11%)留秆(7.96%)玉米秸秆覆盖(3.01%)。研究结果可为南疆冬季休闲期棉田土壤水热盐调控提供科学依据。     

土壤水氮资源的利用与管理 Ⅱ-土壤水氮资源的利用、损失和周年利用效率模拟

本文以北京地区冬小麦夏玉米种植制度为背景,应用作物土壤联合模型,模拟了不同水氮管理措施和降雨年型下的周年相对产量、土壤水氮资源利用、损失和周年利用效率,分析了水氮管理措施对它们的影响,以期为合理进行水氮管理,提高周年的产量和土壤水氮资源利用效率服务。     

内蒙古通辽膜下滴灌玉米棵间蒸发量SIMDual_Kc模型模拟

为明确内蒙古东北部地区玉米膜下滴灌棵间蒸发的变化规律,探索玉米膜下滴灌节水增产机制,在田间试验的基础上,采用经过参数率定与验证的双作物系数SIMDual_Kc模型,模拟分析了土壤含水率、土壤棵间蒸发及作物系数的变化规律,结果表明:1)双作物系数SIMDual_Kc模型模拟内蒙古东北部地区滴灌玉米土壤含水率与实测值具有很好的一致性;2)利用双作物系数SIMDual_Kc模型估算出该地区覆膜玉米生育初期、中期和后期作物系数分别为0.15、1.05、0.4,无膜滴灌玉米初期、中期和后期作物系数分别为0.15、1与0.4;3)根据双作物系数模型SIMDual_Kc模拟了2014和2015年滴灌玉米棵间蒸发量占作物蒸散发的比例,覆膜滴灌较无膜滴灌少,说明覆膜能有效降低作物棵间蒸发量,具有降低作物耗水量的潜在优势。研究结果可以为内蒙古东北部地区玉米滴灌生产实践提供科学依据。     

Winter cover cropping influence on nitrogen mineralization,presidedress soil nitrate test,and corn yields

The mineralization and availability of cover crop N to the succeeding crop are critical components in the management of soil N to reduce N leaching. The effects of several leguminous and non-leguminous cover crops on soil N availability, N mineralization potential, and corn (Zea mays L.) yield were examined. The cover crops had variable effects on soil N availability and corn yield and N uptake. Because of the rapid mineralization of the cover crops following incorporation, the inorganic N levels in the soil sampled in mid-May 1992 (4 weeks after incorporation of cover crops), rather than the potentially mineralizable N, rate constants, initial potential mineralization rate, or cumulative N mineralized over 14 weeks, correlated well with N concentrations, C:N ratios, or the N added in the cover crops. However, the inclusion of potentially mineralizable N with inorganic N in a multiple regression improved the variability in the corn yield and the N uptake accounted for. Since extensive mineralization had occurred before the 21 May sampling, the potentially mineralizable N was affected more by the soil organic N and C than by the N concentrations of the cover crops. The presidedress NO₃ ^--N test levels were well predicted by the inorganic and potentially mineralizable N (R ²=0.89, P<0.01), although the test levels were better in predicting corn yield and N uptake. If the available soil N test needs to be made earlier than recommended by the presidedress NO₃ ^--N test, both inorganic and potentially mineralizable N are needed to better predict the corn yield and N uptake in the soils.     

Influence of soil physicochemical and biological properties on the degradation and adsorption of the nematicide fosthiazate

The degradation and adsorption of the organophosphorus nematicide fosthiazate were investigated in nine soils with various physicochemical and biological characteristics. Fosthiazate was more persistent in acidic soils (pH <6), with half-life (t1/2) values ranging from 53.3 to 57.7 days, compared to soils with higher pH (pH >7), with t1/2 ranging from 14.1 to 20.7 days. Application of antibacterial and antifungal antibiotics to soil samples resulted in a significant inhibition of fosthiazate degradation only in two of the three acidic soils. In contrast, soil autoclaving resulted in doubling the t1/2 of fosthiazate in all studied soils, suggesting that both microbial and abiotic processes contribute to fosthiazate degradation. Statistical analysis indicated a significant negative correlation (P < 0.01) between soil pH and t1/2. Fosthiazate was generally weakly adsorbed with Freundlich adsorption coefficient (Kf) values ranging from 1.23 to 2.74 mL/g. Fosthiazate concentration was strongly correlated with soil organic matter content with higher Kf values in soils with higher organic matter content (P < 0.01). The mean t1/2 and Kf values derived from the laboratory studies were used to parametrize the FOCUS groundwater (GW) models PRZM, PELMO, PEARL, and MACRO for nematicide application in potato and tomato crops. Predicted environmental concentrations produced by the models PEARL and MACRO suggested a potential risk for GW in several scenarios, unlike PELMO and PRZM, which predicted low risk for GW. These findings suggest that the environmental fate of fosthiazate is strongly influenced by soil characteristics and that this nematicide should be used with care in acidic, light soils with low organic matter content.     

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。