Shallow Water Table Depth Research Articles

Delineation and characterization of salt-affected soils in Varanasi district of Uttar Pradesh

Salt affected soils are primarily widespread over Uttar Pradesh especially in irrigated areas of the vast middle Indo-Gangetic alluvial plain of shallow water table depth and hot and dry moisture regions. Soil salinity and alkalinity are two of the main constraints present in these irrigated agricultural lands and the problem of salinity and alkalinity increases every year as a result of secondary salinisation and as a result of which the fertile productive land is gradually becoming unproductive. Varanasi district of Uttar Pradesh have been identified to the intensive area study site for this research work. Study area is a part of the vast alluvial expanse popularly known as Indo Gangetic plains. The study area lies in hot semi arid eco region 4.3, between geo-coordinates 25o 18’’ N and 83o 03’’ E covering 1, 535 sq km area a part of the vast Indo-Gangetic alluvial plain having sandy soil, which also coincides with low rainfall. The result indicated that the soil reaction is moderately to strongly alkaline. The organic carbon was reported to vary from 0.11 to 0.88%. Under saturation extract analysis, sodium ion was observed as dominant cation, followed by Calcium, Magnesium and Potassium and alkali soil having high pH are deficient in both soluble and exchangeable calcium.

NO3-N and Metolachlor Concentrations in the Soil Water as Affected by Water Table Depth

Experiments were conducted in lysimeters to study the effect of shallow water table (WT) depths on the transport of two commonly used agricultural chemicals, nitrate-N and metolachlor, to shallow groundwater. Groundwater samples were collected from 0.20-, 0.40-, and 0.60-m depths using suction tubes during the growing season. The results showed significant reductions in both nitrate-N and metolachlor concentrations in the groundwater by maintaining shallow WT depths. Lowest concentrations of nitrate-N and metolachlor in the groundwater were observed when WT were maintained at 0.15-m depth. Generally, nitrate-N concentrations were increased with the soil depth while metolachlor concentrations decreased with the sampling depth during the growing season. Analysis of drainage outflow data at the end of WT treatment period also provided the evidence of the effectiveness of shallow WTs in reducing chemicals losses to shallow groundwater systems. The results of this study indicated that nitrate-N and metolachlor concentrations in the drainage outflow were 54 and 45%, respectively, lower for the 0.15-m WT treatment than the 0.60-m WT treatment. Regression analysis showed a strong negative linear relationship between metolachlor concentration and days after planting (DAP). Soybean yield was significantly reduced with the rise in WT depth. Average soybean yield obtained for the 0.15-m WT depth was 42% lower than the 0.60-m WT depth. It can be concluded from the overall results of this study that shallow WTs can be used effectively to reduce the nitrate-N and metolachlor losses to the shallow groundwater.

Reply to “comment on a model for soil surface evaporation based on Campbell’s retention curve by Zarei et al.” by M. Sadeghi

Sadeghi (2015) has been commented on an analytical solution we derived for evaporation from bare soils with a descending shallow groundwater table (Zarei et al., 2010). The evaporation rate in this solution was described as a function of shallow water table depth drawdown using the parameters of Campbell’s soil water retention model. Sadeghi (2015) took issue with a simplifying assumption in the derivation about the pressure head distribution above the water table that allowed us to obtain the approximate solution. This response aims to demonstrate that the derivation of Zarei et al. (2010) works reasonably well in the presence of a shallow water table by providing a more detailed discussion and additional experimental evidence.

A diagnosis of sub-surface water table dynamics in low hydraulic conductivity soils in the sugar cane fields of Pongola, South Africa

Water and land are the two natural resources restraining crop production in South Africa. With the increasing demand for food, emphasis has shifted from the sole reliance on rain fed crop production, to irrigation. The deterioration in irrigation water quality from surface water sources is, however, posing a big challenge to the sustainability of irrigated crop production. This is because more water is required for leaching, resulting in shallow water tables in agricultural lands. The installation of well designed subsurface drainage systems alone is not enough; the provision of timely maintenance is also necessary. In this study, the extent and severity of problems as a consequence of shallow water tables and their possible causes were investigated at three sugarcane fields in Pongola, South Africa, having low hydraulic conductivity soils. Also investigated were soil salinity levels and the temporal variation in the salinity of the irrigation water. A water table map of a 32 ha sugarcane field was generated, using observed water table depth (WTD) data from 36 piezometers monitored from September 2011 to February 2012. Out of the total 32 ha under cultivation, 12% was found to be affected by shallow WTDs of less than the 1.0 m design WTD. The inability of natural drainage to cope with subsurface drainage needs and the poor maintenance of subsurface drainage systems contributed to the shallow water tables in the area. Furthermore, the currently adopted drainage design criteria also proved unsatisfactory with mean observed water table depth and drainage discharge (DD) of 20% and 50%, respectively, less than their respective design levels. The salinity of the irrigation water was, on average, 32% higher than threshold tolerance level of sugarcane. The root zone soil salinity levels at the three study sites were greater than the 1.7 dS m−1 threshold for sugar cane. The subsurface drainage design criteria adopted at the site needs to be revisited by ensuring that the slope of the land is taken into consideration in the drainage design in addition to adhering to a recommended maintenance schedule.

Simulation of groundwater evaporation and groundwater depth using SWAT in the irrigation district with shallow water table

In irrigation districts with shallow water table, groundwater evaporation (ETgw) and groundwater depth are important variables for the study of water balance. These variables are influenced by natural factors and human activity. In this study, a new method of simulating ETgw was used for SWAT, and the computing and output modules of groundwater depth were established. In addition, based on simulations, we analyzed the influences of irrigation schedules and soil types on ETgw and groundwater depth in the Irrigation Districts along the Lower Reach of Yellow River Basin. The applicabilities of the three methods (Hargreaves, Priestley-Taylor and Penman-Monteith) simulating potential evapotranspiration in SWAT 2000 were evaluated by the measured groundwater evaporation, and Hargreaves was applied in the simulation for irrigation district due to its smallest simulation error. The results presented that the mean groundwater depth decreased with the increase of irrigation amount. However, the changes of soil water storage in root zone and groundwater depth might have more complex effects on the variation of the mean groundwater evaporation. Loamy sand had the smallest annual mean groundwater depth and mean annual ETgw in the study area, while silt loam corresponded to the largest groundwater depth and groundwater evaporation. This study provides a new method for making simulations and analyses of the hydrological cycle in irrigation districts which has a shallow water table.

A simple, regionally parameterized model for predicting nonpoint source areas in the northeastern US

Abstract Study Region Ten watersheds in New York, New Jersey, and Pennsylvania, USA. Study Focus A three parameter model based on variable source areas (VSAs) that does not require calibration within the region, was developed and tested. The model maintains a lumped daily water budget, but distributes runoff spatially using a soil topographic index (STI). We used ten gauged watersheds across the region to establish the model parameters, and compared model predicted VSAs against shallow water table depth and surface soil moisture field measurements in three sites. New Hydrological Insights for the Region The model was able to correctly predict VSAs at all three monitoring sites, indicating that saturation-excess runoff is important in these watersheds. The pattern of error in the model suggests that lateral subsurface flow paths could be exerting an influence on overland runoff generation in a way that is not captured by a static STI. The model has potential to be used as part of a strategy to limit nonpoint source pollution from saturation-excess runoff dominated areas in the region, and has been incorporated into an online decision support tool in central NY (www.hsadss.bee.cornell.edu).

Modelling effects of seasonal variation in water table depth on net ecosystem CO<sub>2</sub> exchange of a tropical peatland

Abstract. Seasonal variation in water table depth (WTD) determines the balance between aggradation and degradation of tropical peatlands. Longer dry seasons together with human interventions (e.g. drainage) can cause WTD drawdowns making tropical peatland C storage highly vulnerable. Better predictive capacity for effects of WTD on net CO2 exchange is thus essential to guide conservation of tropical peat deposits. Mathematical modelling of basic eco-hydrological processes under site-specific conditions can provide such predictive capacity. We hereby deploy a process-based mathematical model ecosys to study effects of seasonal variation in WTD on net ecosystem productivity (NEP) of a drainage affected tropical peat swamp forest at Palangkaraya, Indonesia. Simulated NEP suggested that the peatland was a C source (NEP ~ −2 g C m−2 d−1, where a negative sign represents a C source and a positive sign a C sink) during rainy seasons with shallow WTD, C neutral or a small sink (NEP ~ +1 g C m−2 d−1) during early dry seasons with intermediate WTD and a substantial C source (NEP ~ −4 g C m−2 d−1) during late dry seasons with deep WTD from 2002 to 2005. These values were corroborated by regressions (P < 0.0001) of hourly modelled vs. eddy covariance (EC) net ecosystem CO2 fluxes which yielded R2 > 0.8, intercepts approaching 0 and slopes approaching 1. We also simulated a gradual increase in annual NEP from 2002 (−609 g C m−2) to 2005 (−373 g C m−2) with decreasing WTD which was attributed to declines in duration and intensity of dry seasons following the El Niño event of 2002. This increase in modelled NEP was corroborated by EC-gap filled annual NEP estimates. Our modelling hypotheses suggested that (1) poor aeration in wet soils during shallow WTD caused slow nutrient (predominantly phosphorus) mineralization and consequent slow plant nutrient uptake that suppressed gross primary productivity (GPP) and hence NEP (2) better soil aeration during intermediate WTD enhanced nutrient mineralization and hence plant nutrient uptake, GPP and NEP and (3) deep WTD suppressed NEP through a combination of reduced GPP due to plant water stress and increased ecosystem respiration (Re) from enhanced deeper peat aeration. These WTD effects on NEP were modelled from basic eco-hydrological processes including microbial and root oxidation-reduction reactions driven by soil and root O2 transport and uptake which in turn drove soil and plant carbon, nitrogen and phosphorus transformations within a soil-plant-atmosphere water transfer scheme driven by water potential gradients. Including these processes in ecosystem models should therefore provide an improved predictive capacity for WTD management programs intended to reduce tropical peat degradation.

Predicting Shallow Water Table Depth at Regional Scale: Optimizing Monitoring Network in Space and Time

Shallow water table levels can be predicted using several approaches, either based on climatic records, on field evidences based on soil morphology, or on the outputs of physically based models. In this study, data from a monitoring network in a relevant agricultural area of Northern Italy (ca. 12,000 Km2) were used to develop a data driven model for predicting water table depth in space and time from meteorological data and long-term water table characteristics and to optimize sampling density in space and time. Evolutionary Polynomial Regressions (EPR) were used to calibrate a predictive tool based on climatic data and on the records from 48 selected sites (N = 5,611). The model was validated against the water table depths observed in 15 independent sites (N = 1,739), resulting in a mean absolute error of 30.8 cm (R2 = 0.61). The model was applied to the whole study area, using the geostatistical estimates of the average water table depth as input, to provide spatio-temporal maps of the water table depth. The impact of the degradation of data input in the temporal and spatial domain was then assessed following two approaches. In the first case, three different EPR models were calibrated based on 25 %, 50 % and 75 % of the available data, and the error indexes compared. In the second case, an increasing number of monitoring sites were removed from the initial data set, and the associated increased kriging standard deviation was assessed. Reducing the average sampling frequency from 1.5 per month to 1 every 40 days did not impact significantly on the prediction capability of the proposed model. Reducing the sampling frequency to 1 every 4 months resulted in a loss of accuracy <3 %, while removing more than half locations from the network, resulted in a global loss of information <15 %.

Qualitative Land Suitability Evaluation for the Growth of Rice and Off-seasons Crops as Rice Based Cropping System on Paddy Fields of Central Guilan, Iran

Land suitability evaluation analysis is a necessecary to achieve optimum management and utilization of the available land resources for sustainable agricultural crops production. One of the most serious and urgent constraint in lowland paddy fields of Iran is to improve agricultural land management and cropping patterns either to increase the agricultural production with proper land use resources or to get more income from out of season plant as a second crops.Therefore, the objective of this study was to find the most suitable off-season crops after rice. Qualitative Land Suitability (QLS) classification of fifteen first and second agricultural crops in the paddy fields of the Guilan plain in Iranunder RBCS that covers an area of 40567 ha was carried out. By using the semi-detailed method of soil classification, 24 soil unites at 11 soil series in five different physiographic units were indentified (river alluvial plains (5 series), low lands (2 series), river banks (2 series) and coastal plains and sand dunes (2 series)). Land and climate characteristics of each crop with its requirements were also determined and rated based upon Parametric and simple limitation method proposed by Sys et al. [1]. The obtained indexes indicated that land suitability classes varied from S2 (moderately suitable) to N (Not suitable). The highest land suitability class for crops are: S2 for Rice, Spinach, Beans, Radish, Garlic, Shall cress, Clover, Lettuce, Rape seed, Bean (vulgaris and faba cultivars) and S3 for Wheat, Carrot, Barley, Triticale, and Rice (Ratoon). The most important limiting factors are: climate (low temperature and high rainfall at vegetative and reproductive growth stages), drainage (shallow water table depth), soil (texture) and fertility (low organic carbon content, pH) (alone or in combination) respectively, those influence adversely on the land suitability classes, especially climatic and drainage limitation, because of growing season in autumn and winter Verification of the factors and their relative significance is very important for decision on land suitability.Keywords: Land Suitability, Paddy Fields, Rice, Second Crops.

Effect of Water Table Depth on Growth and Yield of Soybean Yudou 16

AbstractIn 2005–2006, a multilysimeter study was conducted to determine the effect of various water table depths (WTDs) (0.2, 0.4, 0.6, 0.8, 1.0, 2.0, 3.0, 4.0, and 5.0 m) on the growth of soybean variety Yudou 16 in the transitional zone of northern semitropical and warm temperate climatic conditions of the Huaibei Plain, Anhui Province, China. In the experiment, precipitation was accounted for and WTD was controlled. The yield of Yudou 16 soybeans was greatest with a WTD of 2 m; yield decreased when the WTD was deeper or shallower than 2 m. From 0.2 through 2.0 m soybean yield increased rapidly with increasing WTD because shallow WTDs produced an oversupply of water in the root zone. From 2 through 5 m yield decreased slowly with increasing WTD under the experimental conditions. This was apparently because deeper WTDs could not compensate (through phreatic evaporation) for rainless periods of moisture stress during the growing season. When the constant WTD changes from 0.8 to 4.0 m, the yield is equal t...

Foundation Assessment in Different Parts of Iraq Using STAAD Pro V8i

Foundation is considered as one of the main parts of any structure. The type of foundation used is highly dependent on the type and properties of soil. The design of foundations requires many factors that should be defined. There are number of differences in the geological and soil conditions in Iraq. As a consequence, these differences are reflected on the type of foundation to be used. Despite these differences, same materials and style of buildings are used all over Iraq. The main problems of Iraqi soil are high gypsum content, salinity and shallow water table depth. These factors that influence the foundations are the soil properties and the amount of loads that transmitted by the superstructure. The situation has been analysed through a case study which illustrated the link between soil and foundation types in three different parts of Iraq (Mosul, Baghdad and Basra). One building was analysed using STAAD (structural analysis and design). Pro software in these regions. It is evident that Iraqi designers and engineers require local code to define all the loads, materials and design of the foundation to be used. The use of local materials might be very effective from both engineering and economic perspectives.

Assessment of evaporation and salt accumulation in bare soil: Constant shallow water table depth with saline ground water

Salinization of soil is a major problem in arid and semi-arid regions with saline shallow water table. This is influenced by climate, soil type, crop, irrigation water quality and management practice, depth of water table and salinity of the water table. The objective of this study was the assessment of evaporation and salinization of bare soil profile with various water table depths including 300, 500 and 800 mm by saline groundwater (3 g NaCl/L + 3.5 g CaCl2/L). In this research we were monitoring amount of evaporation from bare soil, and observing profiles of soil water and salinity over periods of up to 80 days. The experiments started on April, 10th, 2010. Results showed that, salts mainly accumulated in the soil surface and volume of evaporation from bare soil in lower water table depth (D = 300 mm) is greater than other lysimeters (D = 500 and 800 mm), and salt accumulation in this lysimeter was higher than others. After 80 days, amount of salinity (ECe) in soil surface was 83.84, 65.76 and 24.05 dS/m, for D = 300, 500 and 800 mm, respectively. Key words: Evaporation, salinity, water table.

Predicting shallow water table depth at regional scale from rainfall and soil data

Summary Shallow water table levels can be predicted using several approaches, based either on climatic records, on field evidences based on soil morphology, or on the outputs of physically based soil–water balance models. In this study, data from a water table monitoring network were used to develop an empirical method for predicting water table depth in space and time from a soil map, cumulative rainfall data and long term water table characteristics, in order to optimize irrigation management at regional scale. Records of 160 piezometer sites available from 1997 to 2008 were analyzed to detect the overall temporal trend in water table depth in a relevant agricultural area of Northern Italy (extent of about 12,000 Km 2 ). A clear trend in water table lowering is observed over the 12 years of available observations, with an average rate of 4.5 cm per year. Precipitation data for the years 2004–2008 and the records from 25 selected sites ( N = 2299) for the same period were used to calibrate a predictive tool based on the assumption of a sinusoidal behavior of the water table depth with a bimodal yearly cycle. The proposed model uses as inputs the cumulative rainfall in the previous 365 days to that of prediction and the geostatistical estimates of the long-term (2005–2008) yearly average water table depth and oscillation. The model, calibrated for the whole data set and for subsets of sites grouped in terms of functional soil properties, was validated against the WT depths observed in 7 independent sites during 2005–2008 ( N = 654). Validation results showed a mean absolute error of 37.1 cm for the general model and 33.1 cm for the model calibrated on the soil groups’ subsets. The accuracy of prediction was higher in years with precipitation amounts closer to the observed average. The general model was eventually extended to the whole study area, providing spatio-temporal maps of the water table depth. The results were further validated against the water table depths observed in all the piezometers at three dates in 2009: error statistics computed for the whole set of available readings at the three selected dates ( N = 322), resulted in a mean absolute error of 37.7 cm. Although based on a limited amount of inputs, the accuracy of the proposed models was comparable to the results reported in the literature for more complex models.

Shallow Water Table Depth Algorithm in SWAT: Recent Developments

Knowledge of the shallow water table depth (wtd) is crucial in many studies, including determination of optimum irrigation and drainage management systems for agricultural production, farm machine trafficability, and water quality due to agricultural chemical transport and soil salinity. Therefore, it is essential for hydrologic models to accurately simulate wtd. A shallow wtd algorithm, herein called the modified DRAINMOD approach, that relates drainage volume (vol) to wtd, was recently incorporated into the Soil and Water Assessment Tool (SWAT) model. In the modified DRAINMOD approach, wtd is computed as a function of vol and a water table factor (wt_fctr), which converts vol into wtd. The constant wt_fctr is currently a calibration parameter. However, at the watershed scale where there are many fields (hydrologic response units, HRUs), it is difficult if not impossible to determine an optimum wt_fctr value for each HRU through the calibration process. The objectives of this study were to: (1) revise the modified DRAINMOD wtd algorithm in SWAT so that wt_fctr is automatically computed by the model as a function of soil physical properties in order to eliminate determination of wt_fctr through the calibration process, and (2) evaluate the revised modified DRAINMOD wtd algorithm within SWAT using measured wtd data for three observation wells located in forest fields within the Muscatatuck River basin in southeast Indiana. On average, the calibrated wt_fctr yielded daily NSE values of 0.64 and 0.41, PBIAS values of -13% and -4%, and RMSE values of 0.41 m and 0.59 m during the calibration and validation periods, respectively, for the three observation wells. The automatically computed variable wt_fctr yielded daily NSE values of 0.66 and 0.58, PBIAS values of 4% and 10%, and RMSE values of 0.40 m and 0.50 m during the calibration and validation periods, respectively, for the same observation wells. Based on these model performance results, there were no significant differences between the wtd simulated using the manually calibrated constant and the automatically computed variable wt_fctr values. The automatically computed variable wt_fctr will enable the revised modified DRAINMOD shallow wtd algorithm to be used at the watershed scale.

Soil and Water Assessment Tool (SWAT) Hydrologic/Water Quality Model: Extended Capability and Wider Adoption

This article introduces a special collection of 16 research articles on new developments and applications of the Soil and Water Assessment Tool (SWAT) to address various environmental issues at a range of geographic and temporal scales. Highlights include addition of a subdaily erosion and sediment transport algorithm, a biozone module, and a new algorithm for shallow water table depth. Model applications include climate change impact assessments, model adaptation to regional environmental conditions, watershed-scale soil erosion assessments, and linkages to other models. A summary of reported model performance indicates that 85% of daily flow calibration statistics reported in this collection were satisfactory or better, with very good performance in four of the 20 calibration results and in three of the 19 validation results. Details of reported model parameters for calibration of flow and water quality constituents are provided for other SWAT modelers. This collection builds upon a previous ASABE 2010 SWAT Special Collection, demonstrating continued developments to enhance SWAT's capabilities and highlighting SWAT's continued expansion in international applications, especially in Asia.

Influence of toposequence position on stem growth, branching habit and root yield of cassava in inland valley ecology

Cassava is grown in both upland and inland valley ecologies (IVS).Water table depths in IVS significantly influence the productivity of cassava. A trial was conducted to evaluate the effects of toposequence position in inland valley ecology on stem growth, branching habit and root yield of cassava using a 4 x 4 Latin Square design. There were significant differences among cultivars, toposequence positions, sites and years for stem growth parameters and root yield. High yielding cultivars (TMS 91/02324 and TMS 91/02327) were short and late branching, had one branching level and big stems, while low yielding ones (TMS 4(2)1425 and landrace) were early branching and had up to three branching levels. Cultivars with low branching habit produced higher number of stems than the profuse branching ones. Stem number correlated positively with yield at shallow water table site, indicating its importance as yield determinant in less branching cultivars at shallow water table depth. The number of branching levels and height to second and third branching levels correlated negatively with yield at shallow water table, suggesting that yield reduction due to high number of branches was more severe at shallow than deep water table. Drought stress stimulated forking in less branching cultivars, but reduced branching in high branching ones. Shallow water table and drought stress reduced stem number, stem size, height to forking and plant height, but the reduction was lower for high than low yielding cultivars. Therefore, stem growth parameters were generally higher in the valley fringe with deeper table than in the other positions with shallow water table. Keywords: Root yield, water table, Stem growth, Branching habit, Cassava, Inland valley

Forestry applications of ground-penetrating radar

Ground-penetrating radar (GPR) is a geophysical and close-range remote sensing technique based on the use of radar pulses to obtain cross-section images of underground features. This method is characterized by the transmission of an electromagnetic short length pulse (1-2 ns), presenting a centre frequency ranging from 10 MHz to 2.5 GHz. The principles of GPR operation are based on the ability of low frequency radar waves to penetrate into a non-conductive medium, usually subsoil, but also walls, concrete or wood. Those waves are detected after suffering a reflection in electromagnetic discontinuities of the propagation medium. Therefore, this is a suitable method to study changes in those physical properties, and also to characterize different mediums and the reflective targets providing information about their physical properties. The aim of this work is to describe and demonstrate different applications of GPR in forestry, showing the obtained results together with their interpretation. Firstly, in this paper, it is illustrated how GPR is able to map shallow bedrock, subsoil stratigraphy and also to estimate shallow watertable depth. Secondly, different tree trunks as well as dry timber are analyzed, evaluating the different radar data obtained in each particular case, and observing differences in their electromagnetic properties related to the GPR response. Finally, several measurements were taken in order to analyze the use of GPR to detect tree root systems using polarimetric techniques, being possible to detect medium and big size roots, together with groups of small roots.

Fine-root growth, fine root mortality, and leaf morphological change of Populus alba in response to fluctuating water tables

Water table fluctuation in arid land regions may alter tree fine-root growth and mortality, thereby affecting leaf growth. To reveal the effects of water table fluctuation on fine-root growth and mortality and their relation to leaf growth, we exposed P. alba L. cuttings to various fluctuating water table depths. 1-year-old rooted cuttings were grown individually in pots containing sandy soil in a greenhouse in three water table depth treatments for 45 days: constant depth at 45 cm from the soil surface, fluctuating depths between 45 and 30 cm, and fluctuating depths between 45 and 15 cm. Fine-root biomass and mortality, biomass partitioning among plant parts, and whole-tree growth responses were determined in cuttings harvested every 15 days. Fluctuation of water tables increased the mortality of fine roots at the layers near the soil surface. Fine-root mortality increased during the shallower water table depth period. At the whole-root system level, although fine-root mortality increased when the water table was shallower, fine-root biomass was similar among the treatments, suggesting that P. alba cuttings would sustains its standing fine-root biomass under fluctuating water table depth conditions. Our structural equation modeling showed the fine-root proportion affects leaf morphological changes, suggesting that there would be a parallel relationship of morphological changes between roots and leaves with fluctuating water tables.

Responses of saltcedar (Tamarix chinensis) to water table depth and soil salinity in the Yellow River Delta, China

Significant studies about Tamarix chinensis as an introduced invasive plant species have been implemented in North America. However, the response of native T. chinensis to its environment is not well known in China. T. chinensis is a useful species in preventing sea water intrusion in coastal areas of northern China. It is necessary to fully understand the relationships between environmental conditions and ecological characteristics of this species to better preserve its habitats. The Yellow River Delta Natural Reserve, one of the major distribution regions of T. chinensis, was then selected as a case study area to investigate the response of this species to water table depth and soil salinity (Na+, Cl−, Mg2+). It was found that sites with shallow water table depths (less than 1.5 m) and low soil salinity (less than 30 psu), provided the best habitat conditions for T. chinensis. The results also showed that plant height, stem diameter, and crown width were all positively correlated to plant age, while they had negative correlations with water table depth. Negative correlations between plant height and soil salinity, plant stem diameter and soil salinity were also concluded. However, no obvious relationship between the crown breadth of T. chinensis and soil salinity was observed. Four types of T. chinensis habitats were obtained based on the ecological characteristics of T. chinensis individuals associated with soil salinity and water table depth, i.e., (1) Low water table with high soil salinity; (2) Deep water table with high soil salinity; (3) Deep water table with low soil salinity; (4) Inundation with low salinity. These results provide a sound basis for wetland management in the Yellow River Delta.

Accumulation and distribution of dry matter in relation to root yield of cassava under a fluctuating water table in inland valley ecology

Cassava an important staple food is grown both in upland and inland valley in the tropics. A trial to assess dry matter production and partitioning in relation to root yield was conducted in 3 positions along inland valley toposequence using 4 x 4 Latin square design. Dry matter partitioning differed among cultivars, toposequence positions, sites and years due to differences in water table depth and weather conditions. High dry matter partitioning to leaves, stems, fibrous roots and rootstocks reduced yield, while high biomass allocation to storage roots increased yield. High dry matter partitioning to leaves reduced yield more in the landrace likely due to low sink capacity. Partitioning high dry matter to leaves reduced yield more at deep than shallow water table depth. Excess moisture stress increased dry matter accumulation in rootstock, fibrous and storage roots, but decreased partitioning to stems and leaves. Drought stress reduced dry matter allocation to storage roots, but increased partitioning to rootstocks, fibrous roots and stems. TMS 91/02324 and TMS 91/02327 with lowest dry matter accumulation in stems and fibrous roots and highest in storage roots had the highest yields and therefore better adapted to inland valley conditions.