Chromium-resistant microorganisms isolated from evaporation ponds of a metal processing plant

Chromium occurs naturally at trace levels in most soils and water, but disposal of industrial waste and sewage sludge containing chromium compounds has created a number of contaminated sites, which could pose a major environmental threat. This study was conducted to enumerate and isolate chromium-resistant microorganisms from sediments of evaporation ponds of a metal processing plant and determine their tolerance to other metals, metalloids and antibiotics. Enumeration of the microbiota of Cr-contaminated sediments and a clean background sample was conducted by means of the dilution-plate count method using media spiked with Cr(VI) at concentrations ranging from 10 to 1000 mg L^?1. Twenty Cr(VI) tolerant bacterial isolates were selected and their resistance to other metals and metalloids, and to antibiotics was assessed using a plate diffusion technique. The number of colony-forming units (cfu) of the contaminated sediments declined with increasing concentrations from 10 to 100 mg L^?1 Cr(VI), and more severely from 100 to 1000 mg L^?1 Cr(VI). The background sample behaved similarly to 100 mg L^?1 Cr(VI), but the cfu declined more rapidly thereafter, and no cfu were observed at 1000 mg L^?1 Cr(VI). Metals and metalloids that inhibited growth (from the most to least inhibitory) were: Hg > Cd > Ag > Mo = As(III) at 50 μg mL^?1. All 20 isolates were resistant to Co, Cu, Fe, Ni, Se(IV), Se(VI), Zn, Sn, As(V), Te and Sb at 50 μg mL^?1 and Pb at 100 μg mL^?1. Eighty-five percent of the isolates had multiple antibiotic resistance. In general, the more metal-tolerant bacteria were among the more resistant to antibiotics. It appears that the Cr-contaminated sediments may have enriched for bacterial strains with increased Cr(VI) tolerance.     

Denitrification characteristics of pond sediments in a Chinese agricultural watershed

Ponds are widely distributed in rice-based agricultural watersheds, particularly in southern China, and may play an important role in nitrate (     ) removal. However, the denitrification rate of pond sediment, measured using the acetylene (C₂H₂) inhibition technique, indicated that the amount of nitrogen removed by denitrification accounted for <1% of the total nitrogen applied. The present study was undertaken to determine the effects of sediment depth and temperature on denitrification of pond sediment using the C₂H₂ inhibition technique. The highest denitrification potential was found in the upper 5 cm of sediment, but this only accounted for approximately 34% of the total denitrification of the upper 0–30 cm of sediment, suggesting that sediment denitrification potential would be underestimated if only the upper 5 cm of sediment was measured. The denitrification potential was low and showed a weak response over a temperature range of 6–18°C, whereas denitrification increased significantly from 18 to 30°C, indicating that denitrification may play an important role in the removal of     in warm seasons. A comparison of the     disappearance and C₂H₂ inhibition methods showed that they were significantly ( P  < 0.01) and positively correlated. However, the C₂H₂ inhibition method gave only approximately 25% of the values determined by the     disappearance method.     

兼顾排涝标准与水质净化要求的农业圩区最优水面率确定

针对农业圩区的排涝以及水环境问题,该研究以江苏里下河地区为研究对象,以满足里下河圩区设计排涝标准与水质净化要求为目标,构建农业圩区坑塘-排水沟道湿地系统最优水面率数学模型。模型以工程系统总费用现值最小为目标函数,以泵站涝水外排能力与圩内水面率、水面率上下限、水环境容量与圩内坑塘与排水沟道系统的关系（主要包括圩内坑塘沟道湿地系统对总氮、总磷以及铬的化学需氧量的去除率）等为约束条件,以圩内坑塘（湖泊）水面率、排水沟道水面率、外排涝水泵站设计排涝流量为决策变量,采用遗传算法对模型进行求解。对江苏里下河地区阜宁县渠南灌区的圩区河湖与排水工程系统进行实例优化分析可知：当采用明沟排水系统,圩内总水面率为11.35%（其中坑塘、排水沟道系统水面率分别为8.15%、3.20%）、设计排涝模数为0.86 m3/(s·km2)时,工程建设费用现值最小;此时,圩区可达到20年一遇设计排涝标准、且圩外周边水体为V类时,圩内水体可达到IV类水标准。该方法可为同类地区在国土整治、防洪排涝规划、河湖水体净化等提供参考。     

除氮生物反应器净化农田排水的研究及应用潜力分析

农田排水氮素输出是造成水环境污染的重要原因。近年来涌现的生物反应器除氮技术通过在排水末端增设固体碳源装置,将农田排水部分或全部导入后,使其中的硝态氮通过反硝化反应得到去除。该文回顾了国际上现有生物反应器净化农田排水的研究进展,并分析了农田生物反应器在中国南方湿润区应用的潜力。现有研究结果表明,除氮生物反应器可以有效净化排水水质,平均每年可降低23%～98%的氮素负荷;是一种占地面积少且水质净化效率高的农田控污措施。生物反应器的除氮效果与农田排水过程密切相关,并受到介质特性、入流、出流条件以及环境因子等的影响。中国南方平原作物生长及排水过程相对集中,气象等环境条件非常适于生物反应器的反硝化反应。如何因地制宜确定反应器安装位置与设计尺寸,筛选填料介质,并通过对排水过程的调控来优化生物反应器的除氮效果是需要进一步研究的问题。生物反应器系统后期管理与内部反应动态监测是保证系统正常运行的重要手段。利用生物反应器来净化农田排水具有良好的应用前景,该文可为推动生物反应器在中国的应用研究以及排水污染治理提供理论依据与技术支撑。     

Characterisation of agricultural drainage ditch sediments along the phosphorus transfer continuum in two contrasting headwater catchments

Purpose

This study investigated the phosphorus (P) source, mobilisation and transport potential of ditch bed sediments as well as surrounding field and bank soils in two agricultural headwater catchments with contrasting soil drainage capacities. This information is important for discerning the potential for ditches to attenuate or augment transfers of P from upstream sources and thus for developing appropriate management strategies for these features.

Materials and methods

Phosphorus sources were characterised using the Mehlich3-P, water-soluble P and total P tests. Phosphorus mobilisation potential was characterised using the Mehlich3-AL/P, Mehlich3-Ca/P and DESPRAL P tests. Phosphorus transport potential was characterised using data collected on the presence/absence of surface water in ditches during field surveys and downstream turbidity data.

Results and discussion

Ditch sediments had similar P source contents (Mehlich3-P, water-soluble P and total P) to the surrounding field soils and higher P contents than bank soils. However, calcium contents of sediments in the poorly drained catchment reflected the deep sub-soils rather than the surrounding field and bank soils. Mehlich3-Al/P and Mehlich3-Ca/P contents of ditch sediments in the well (non-calcareous) and poorly (calcareous) drained catchments respectively indicated potential for P retention (above thresholds of 11.7 and 74, respectively). However, sediments were less aggregated than field soils and may mobilise more particulate P (PP) during rain events. Nevertheless, the majority of surveyed ditches dried out from March to September 2011; thus, their potential to mobilise PP may be less important than their capacity to attenuate soluble and PP during this time.

Conclusions

In these and similar catchments, soluble P attenuation and particulate P mobilisation should be maximised and minimised, respectively, for example, by cleaning out the sediments before they become saturated with P and encouraging vegetation growth on ditch beds. This study also highlighted the influence of deep sub-soils on soluble P retention in ditches and thus the utility of characterising soils below depths normally included in soil classifications.

     

Historical distribution of DDT residues in pond sediments in an intensive agricultural watershed in the Yangtze-Huaihe region,China

Purpose

The extensive use of chemical pesticides on farmlands during the last several decades in China has led to a rapid deterioration of environmental water quality in recent years. The aims of this study were to: reconstruct the history of pesticide residues, determine the input load and residual load of dichlorodiphenyltrichloroethane (DDT) pesticides, and assess the risk of pesticide residues to aquatic ecosystem and human health.

Materials and methods

Caesium-137 was used to date sediment cores collected from ponds representing four land use types of an agricultural watershed with high-yield grain production and characterized by multipond systems in the Yangtze-Huaihe region of China. These ponds were selected to establish the historic pattern of DDT pesticide residues.

Results and discussion

(1) The mean total concentration of DDT residues including p,?p?′-dichlorodiphenyldichloroethylene (p,p′-DDE), p,?p?′-dichlorodiphenyldichloroethane ( p,p′-DDD), o,p′-DDT, and p,p′-DDT in sediment in the watershed was 82 μg kg^?1, ranging from under the detection limit to 457 μg kg^?1, which was mostly contributed by p,?p′-DDE (57 μg kg^?1 on average). Spatially, total concentrations of DDT residues in farmland pond sediment were the highest, reaching as high as 457 μg kg^?1. Temporally, an inflection point appeared in the 1970s, prior to which DDT contents increased with time, after which concentrations showed a decreasing trend. (2) In total, 323 kg DDT pesticide was applied to the Liuchahe Watershed since 1955. The total retention of four DDT residues in the multipond system was 14 kg (～4 % of the input), and most DDT pesticide was degraded to p,?p?′-DDE. (3) More than 80 % of sediment DDT residues exceeded their interim freshwater sediment quality guidelines, and the percentages of DDT,DDD, and DDE residues exceeding probable effect limit (PEL) values were 57, 29, and 70 %, respectively, which indicated a moderate to high ecological risk of DDT in this watershed.

Conclusions

Our results clearly reveal that the extensive use of pesticides has resulted in significant pesticide residual pollution in this watershed, which could severely deteriorate water quality and threaten aquatic ecosystem and human health in the watershed and, thus, remain a cause for concern.     

盐碱地排水沟蓄水后底泥与水体盐分交换试验

因长期累积效果,盐碱地排水沟内盐分含量不断升高,危及排水沟系统的生态功能,利用淡水定期进行稀释可延缓盐分累积过程。该文以陕西富平县卤泊滩盐碱地改良区为例,通过实验室土柱试验,研究了排水沟蓄集淡水、水体保持静态条件下,底泥与上覆水体的盐分交换规律,揭示了底泥盐分释放的内在机理。研究结果表明,在分子扩散作用下底泥-上覆水界面之上10cm的范围内存在一个高盐分渐变区(即扩散边界层),10cm以上的水体盐分基本一致;分子扩散是边界层内盐分运移的主要机制;扩散边界层对底泥盐分释放具有一定的阻滞作用,并且随着边界层厚度的增加,阻滞效应也显著增强;底泥盐分释放通量符合负的幂指数形式。     

Occurrence of 12-methyltridecanal in microorganisms and physiological samples isolated from beef

12-Methyltridecanal (MT) smelling tallowy, beef-like was formed from plasmalogens when beef was boiled. To clarify the origin of MT, its concentration was determined by a stable isotope dilution assay in bacteria and protozoa isolated from the rumen of bovine animals as well as in the plasma, erythrocytes, and other physiological samples. The highest amounts of MT were found in bacteria followed by protozoa. The MT content of the erythrocytes was small. The results support the hypothesis that microorganisms are the main source of MT of which a small amount is resorbed by the animal and transported to the muscular tissue where MT is incorporated into plasmalogens.     

稻田-沟塘系统水氮动态模拟与灌排调控模型构建

沟塘系统对农田排水具有较好的拦蓄能力,是降低中国南方稻区农业面源污染风险的有效措施,定量化评价稻田-沟塘系统水氮过程是合理制定水氮管理措施的关键。该研究以稻田-作物模型WHCNS_Rice为基础,通过添加沟塘水氮平衡和灌排调控过程,构建了稻田-沟塘系统水氮调控模型。并采用太湖流域2 a不同灌排和施肥处理的田间试验数据校准和验证模型,分析不同灌排和施肥处理下稻田-沟塘系统的调控策略。研究结果显示,模型能够模拟不同灌排和施肥处理下稻田土壤含水量、稻田田面水深、径流量、氮素径流损失量、氨挥发量、作物吸氮量和作物产量,模拟的相对均方根误差、一致性指数和模型模拟效率的范围分别为4.6%～29.7%、0.758～0.996和0.073～0.983,均在可接受的范围内。模拟结果显示,与传统处理相比,控制灌溉结合优化施肥,减少了稻田32.1%～36.2%的灌溉水用量和36.7%～67.3%的氮素径流损失,同时平均降低了55.1%沟塘硝态氮浓度,从而降低了沟塘地表氮素径流损失风险。Morris敏感度分析结果显示,稻田土壤水力学参数和沟塘渗漏速率对沟塘水深的模拟影响较大,而作物参数的敏感度相对较低。沟塘硝态氮浓度对稻田水力学参数、沟塘氮素消纳系数和氨挥发一阶动力学系数较敏感。同时,构建的模型能反映不同水氮管理措施和沟塘/稻田面积比下稻田-沟塘系统水分消耗、氮素去向和作物生长过程。该模型可为优化稻田-沟塘系统水氮管理方案、防控农业面源污染提供有力工具。     

Factors affecting reduction of selenate to elemental selenium in agricultural drainage water by Enterobacter taylorae

Microbial reduction of selenate [Se(VI)] to elemental selenium [Se(0)] is a useful technique for removing Se from agricultural drainage water. A series of batch experiments were conducted in the laboratory to determine the effects of yeast extract (50-1000 mg/L), salinity (EC, 5-75 dS/m), and NO(3)(-) (5-100 mg/L) on the removal of Se(VI) (2000 microg/L) from drainage water by Enterobacter taylorae. Results showed that relatively high amounts of yeast extract (500 mg/L) were needed for E. taylorae to effectively reduce Se(VI) to Se(0). During a 7-day experiment, approximately 95% of added Se(VI) was reduced to Se(0) in the low-salinity drainage water (5 dS/m) with NO(3)(-) values of 5-50 mg/L. In the high-salinity drainage water (50-75 dS/m), reduction of Se(VI) to Se(0) was limited. E. taylorae was also capable of reducing Se(VI) to Se(0) in the San Joaquin Valley drainage water, with a reduction of the added Se(VI) to Se(0) (73.8%) and Se(-II) (20%). This study suggests that E. taylorae may be used to treat Se(VI)-contaminated drainage water in the field.     

Surfactants and soil water evaporation and migration

1. Water evaporation from soil and sand columns is smaller when the surfactant is placed on the surface, and larger when it is located at the bottom. Water evaporation from soil and sand mixed with the surfactant is as high as without the surfactant. 2. The fact that water evaporation from soil and sand depends on the location of the surfactant in the column is accounted for by the dominant role of migration but not by the suppressive action of the surfactant film on water evaporation. 3. Water migration from sites with surfactant towards sites without surfactant is caused by two pressures: the capillary and the additional pressure arising from the spreading of the surfactant. 4. The importance of the additional pressure on water migration is shown by experiments which rule out the existence of a capillary pressure difference.     

盐碱地农田排水对查干湖承泄区的水质影响评价

为了评价盐碱地农田排水对承泄区的水质影响,该文选取吉林省前郭灌区的农田排水和查干湖承泄区为研究对象,通过2009－2010年水稻生长季每月定期的野外取样、实验分析水样的K+、Na+、Ca2+、Mg2+、SO42-、Cl-、CO32-、HCO3-、总氮、总磷和化学需氧量,研究了查干湖灌溉灌排系统至承泄区相关排水水质的时空变化,并对查干湖水质进行了评价。结果表明,查干湖承泄区对灌排系统的各水质指标有一定的累积效应。目前查干湖水体pH值平均在7.87;钠吸附比最大值（3.59 (mmolc/L)1/2）出现在5月份泡田洗盐期;总氮含量为1.22 mg/L,低于近12年平均值1.56 mg/L;6月份总磷含量最高,达0.28 mg/L。除化学需氧量超标外,其他水质参数未达到浓度限值,但在丰水期查干湖水体已属IV类水质。该研究可为查干湖承泄区的生态环境预警提供理论基础。     

灌排调控的稻田排水中氮素浓度变化规律

基于农田排水氮素浓度及湿地进出口断面总氮（TN）、氨态氮（NH4+-N）、硝态氮（NO3--N）浓度的监测,研究了灌溉排水措施以及沟塘湿地对农田排水中氮素浓度变化的影响。结果表明,控制灌溉的水稻全生育期稻田排水中TN、NH4+-N和NO3--N浓度分别较常规灌溉处理低12.08%、20.33%和13.51%;控制排水处理下稻田排水中TN、NH4+-N和NO3--N浓度分别较常规排水处理低2.21%、7.08%和20.92%;湿地出口水体中TN、NH4+-N和NO3--N浓度分别比入口降低了16.8%、14.4%和50.9%,湿地水体中TN、NH4+-N、NO3--N浓度随时间近似服从指数函数衰减趋势。控制灌溉、控制排水及沟渠塘湿地系统的调控措施对农田排水中氮素的净化效果比较显著。     

Arsenic contents and physicochemical properties of agricultural soils from the Red River Delta,Vietnam

Abstract

To evaluate arsenic (As) levels in agricultural soils of the Red River Delta in northern Vietnam, surface (0–5 cm) and subsurface (20–25 cm) soil samples were collected from 18 paddy and six upland fields on both sides of the river. As a reference, forest soils were also sampled at two sites of the upper river basin. The total As contents of approximately 80% of the surface paddy and upland soils exceeded the maximum allowable limit for Vietnamese agricultural soils (12 mg kg^?1). Arsenic contents higher than 35 mg kg^?1 were found in soils from the Hungyen and Hanam provinces, where high As levels in the groundwater have also been reported. Sequential fractionation of As in these soils indicated that the amounts of As in the phosphate-extractable and residual fractions were higher than those in the forest soils. Elevated total As contents were also detected in the surface soil of a paddy field near a fertilizer factory in Hanoi (site P10). The amount of HCl-extractable As in the surface soil at P10 corresponded to 84% of the total As, while the proportion never exceeded 40% at other locations. In the surface soil at P10, most of the As was part of the phosphate-extractable fraction. Significant correlations between the total As contents of the upland soils and their non-crystalline Fe oxide contents (r = 0.652, P ≤ 0.05) and between As levels of paddy soils and their crystalline Fe oxide contents (r = 0.544, P ≤ 0.01) were observed. Overall, the present study indicated that although serious As pollution was not found in the studied area, there were some point pollutions caused by industrial activities, in addition to some non-point pollutions resulting from high As concentrations in the groundwater. In addition, Fe oxides in the soils are important factors affecting the As contents of agricultural soils in the Red River Delta.     

Incidence of plasmid-linked antibiotic-heavy metal resistant enterics in water-sediment from agricultural and harbor sites

This study assesses the impact of antibiotics used in clinical and veterinary practices, on the incidence of antibiotic- heavy metal resistant enterics in fresh water and sediment from agricultural and harbor sample sites. A total of 848 bacterial strains of the familyEnterobacteriaceae was isolated from agricultural and lake harbor samples and identified to genus level. These were examined for antibiotic-heavy metal resistance. A select smaller number of these isolates were also examined for the presence of plasmids and ability to transfer antibiotic resistance via conjugation or transformation. More than 85 % of the 848 isolates from all four sites were resistant to Ph, Zn, and Co while 5.6% to 16% were resistant to Te and 2.4% to 5.7% to Hg. The ranking of metal resistance according to frequency was the same as the frequency of metal occurrence in sediment samples. Of the total isolates tested, 87% were resistant to six or more antibiotics and 74% were also simultaneously resistant to Co, Zn, and Ph. Testing the resistance of the water isolates to antibiotics used solely in animal husbandry-veterinary medicine indicated that 55.6% of the agricultural isolates possessed resistance to these antibiotics while only 31.9% of the isolates from harbor water showed resistance to the same antibiotics. Of 41 ampicillin resistant isolates examined, 16 (39%)were capable of transferring antibiotic-heavy resistance markers via conjugation. From this same group, plasmid DNA preparations were made. Of these latter preparations, 67% transformed recipientE. coli cells while 58% possessed discernible, often multiple plasmids when examined by gel electrophoresis.     

砂石条形覆盖下土壤水分蒸发动态研究

砂石覆盖已被证实有提高农作物产量的作用,为了研究条形砂石覆盖对土壤水分蒸发的影响,采用精度较高的重力传感器称重测量系统测定水分蒸发动态,进行了5种砂石覆盖度(0%、25%、50%、75%、100%)、2个灌水量(25 mm和35 mm)和2种土壤(砂土和土)的土壤水分蒸发试验。结果表明:砂石覆盖能够有效地抑制土壤蒸发,且抑制作用与砂石覆盖度密切相关。蒸发初期砂石覆盖度越大,日蒸发量越低,但后期日蒸发量趋于稳定(0.6 mm)。相同覆盖度下,土累积蒸发量(Ec)低于砂土。砂石覆盖度增加后累积蒸发量Ec随时间变化过程曲线逐渐降低;同时总蒸发量Et相应减小,蒸灌比也依次减少,蒸发量差ΔE增大,表现为覆盖度为100%的Et仅为裸土的65%左右;裸土的Et占灌水量I的50%左右,而覆盖度为100%的Et占灌水量I的35%左右。Ec与时间的关系符合Gardner理论关系,从而得出Ec与时间和覆盖度的两参量函数关系。     

A model of ammonia volatilization from applied urea. V. The effects of steady-state drainage and evaporation

Rachhpal-Singh & Nye's model of ammonia volatilization is expanded to account for the effects of steady-state water movement by drainage or evaporation when the soil does not dry out to any great extent. The model shows how upward movement of water during evaporation increases volatilization by carrying urea-derived NH₄⁺ and HCO₃^? ions upward, thereby increasing the concentration of ammonia gas at the surface. Conversely, water drainage reduces volatilization by carrying the dissolved solutes into the soil. The model is used to assess the effects on volatilization of evaporating conditions and of irrigation or rainfall.     

潜水埋深为零时塔里木盆地不同土质潜水蒸发与水面蒸发关系分析

根据渭干河灌区潜水蒸发试验站和阿克苏水平衡试验站的实际监测资料，分析了E₆₀₁型蒸发器与E₂₀蒸发皿观测的水面蒸发的关系、不同土质潜水埋深为零时潜水蒸发与水面蒸发的关系，提出了潜水蒸发能力系数的概念，并分析了其与土壤机械组成的关系。结果表明：塔里木盆地非冻结期E₆₀₁型蒸发器与E₂₀蒸发皿观测的水面蒸发的折算系数变化在0.65～0.78之间；除细砂土外，E₆₀₁蒸发器观测的水面蒸发强度不能代替潜水埋深为零时的潜水蒸发强度；不同质地土壤的粉粘粒(d<0.02 mm)含量百分数与潜水蒸发能力系数呈指数相关关系。     

潜水埋深为零时塔里木盆地不同土质潜水蒸发与水面蒸发关系分析

根据渭干河灌区潜水蒸发试验站和阿克苏水平衡试验站的实际监测资料,分析了E601型蒸发器与E20蒸发皿观测的水面蒸发的关系、不同土质潜水埋深为零时潜水蒸发与水面蒸发的关系,提出了潜水蒸发能力系数的概念,并分析了其与土壤机械组成的关系.结果表明塔里木盆地非冻结期E601型蒸发器与E20蒸发皿观测的水面蒸发的折算系数变化在0.65～0.78之间;除细砂土外,E601蒸发器观测的水面蒸发强度不能代替潜水埋深为零时的潜水蒸发强度;不同质地土壤的粉粘粒(d<0.02 mm)含量百分数与潜水蒸发能力系数呈指数相关关系.     

农业小流域毛沟布置方式对氮素径流流失的影响

A comparison experiment was performed, by designing one field ditch (D1 treatment), two field ditches (D2 treatment), three field ditches (D3 treatment), and no field ditch (CK treatment), in an upland of a small agricultural watershed in Nanjing-Zhenjiang hilly regions to observe the farmland surface runoff and N loss characteristics under the different layouts of field ditch. As the layout density of field ditch increased, the drainage effect was improved, the timing of the runoff peak was advanced, and also the peak flow was augmented. At the same time, both the concentration and accumulated transfer flux of total nitrogen (TN) were improved, and thereinto the accumulated transfer fluxes of TN under D3, D2 and D1 treatments were increased by 1.46, 1.34 and 1.16 times, respectively, than that under CK treatment. However, the accumulated transfer fluxes of nitrate-nitrogen (NO3-N) and ammonium-nitrogen (NH+4 -N) under D3, D2 and D1 treatments were reduced by 33.9%, 21.4% and 8.6%, and 35.8%, 24.7% and 12.2%, respectively, compared with those under CK treatment. Under CK treatment, the NO3-N and NH+4-N concentrations were more sensitive to rainfall intensity than the TN concentration. There were significant linear relationships between the transfer fluxes of TN, NO3 -N and NH+4 -N and the runoff flux, with the correlation coefficients of 0.942, 0.899 and 0.912, respectively. In addition, this correlation was also influenced by the layout density of field ditch. Therefore, the environmental effect should be taken into account when designing and constructing field ditches. Especially in the regions of severe fertilizer loss, the approaches of properly increasing the drainage area and decreasing the layout density of field ditch could be adopted under the precondition of avoiding crops from waterlogging.