Functioning of mole drains in a clay soil

Observations of water-table fluctuation and drainflow are reported from a field experiment on a heavy clay soil with replicated “mole-drained” and undrained plots. Results from rainfall events indicated that in both treatments the dominant water movement was through the topsoil which in the drained plots was directly linked to the mole channels probably by fissures.     

Soil water dynamics under various agricultural land covers on a subsurface drained field in north-central Iowa, USA

Modification of land cover systems is being studied in subsurface drained Iowa croplands due to their potential benefits in increasing soil water and nitrogen depletion thus reducing drainage and NO₃-N loss in the spring period. The objective of this study was to evaluate the impacts of modified land covers on soil water dynamics. In each individual year, modified land covers including winter rye-corn (rC), winter rye-soybean (rS), kura clover as a living mulch for corn (kC), and perennial forage (PF), as well as conventional corn (C) and soybean (S), were grown in subsurface drained plots in north-central Iowa. Results showed that subsurface drainage was not reduced under modified land covers in comparison to conventional corn and soybean. Soil water storage (SWS) was significantly reduced by PF treatments during the whole growing seasons and by kC during May through July when compared to the cropping system with corn or soybean only (p < 0.05). Treatments of rC and rS typically maintained higher SWS than C and S, respectively, during the 3 years of this study. In the spring during a 10-15-day period when the rainfall was minimal, SWS in plots with rye, kura clover, and forage decreased at a significantly higher rate than the C and S plots which were bare. Estimated evapotranspiration (ET) during this period was significantly higher in rS, kC, and PF treatments than C and S. The results of this study suggested that significantly higher ET and similar drainage for modified land covers may increase water infiltration, which would be expected to reduce surface runoff thus to decrease stream flow. Because subsurface drainage reduction was not seen in this study, impact of modified land covers on NO₃-N loss needs further investigation.     

Predicting effects of drainage water management in Iowa's subsurface drained landscapes

Long-term hydrologic simulations are presented predicting the effects of drainage water management on subsurface drainage, surface runoff and crop production in Iowa's subsurface drained landscapes. The deterministic hydrologic model, DRAINMOD was used to simulate Webster (fine-loamy, mixed, superactive, mesic) soil in a Continuous Corn rotation (WEBS_CC) with different drain depths from 0.75 to 1.20 m and drain spacing from 10 to 50 m in a combination of free and controlled drainage over a weather record of 60 (1945-2004) years. Shallow drainage is defined as drains installed at a drain depth of 0.75 m, and controlled drainage with a drain depth of 1.20 m restricts flow at the drain outlet to maintain a water table at 0.60 m below surface level during the winter (November-March) and summer (June-August) months. These drainage design and management modifications were evaluated against conventional drainage system installed at a drain depth of 1.20 m with free drainage at the drain outlet. The simulation results indicate the potential of a tradeoff between subsurface drainage and surface runoff as a pathway to remove excess water from the system. While a reduction of subsurface drainage may occur through the use of shallow and controlled drainage, these practices may increase surface runoff in Iowa's subsurface drained landscapes. The simulations also indicate that shallow and controlled drainage might increase the excess water stress on crop production, and thereby result in slightly lower relative yields. Field experiments are needed to examine the pathways of water movement, total water balance, and crop production under shallow and controlled drainage in Iowa's subsurface drained landscapes.     

Effect of mole submergence on the life of mole channels

It has been suggested that submergence of mole channels in field drainage systems will cause their premature collapse and lead to a failure of the system. Limited experience on Field Drainage Experimental Unit's sites has not supported this view.An experiment was set up on a clay soil with a good moling potential, and where a previous moling had lasted up to 5 years. In a pumped drainage scheme submergence was examined to determine if it was a cause of mole channel failure. Isolated plots were subjected to short (usually less than 3 h) and long periods (up to 20 days) of submergence. The hydrological performance and the condition of the mole channels was monitored for 5 years.Short periods of submergence did not appear to have a substantial effect on the mole drainage system and a 4–5-year life of the mole channels could be expected. Longer periods of submergence did not cause any immediate deterioration but the gradual collapse of the roof and side walls, which was the normal mode of failure, became more accentuated. This effect reduced the life of the mole channels to 3–4 years, although 3 years after moling the watertable control of the submerged plots was substantially better than similar adjacent undrained land.     

Effects of controlled drainage on N and P losses and N dynamics in a loamy sand with spring crops

The effects of controlled drainage on N and P losses from soil were examined in a 4-year field drainage experiment on a loamy sand in Southern Sweden. Of the three plots (0.2 ha each), one was drained by conventional subsurface drainage (CD), and two by controlled drainage (CWT1 and CWT2). The groundwater level in the CWT plots was naturally drained to at least 70 cm below the soil surface during the vegetation period between early spring and harvest but allowed to rise to 20 cm below the soil surface during the rest of the year. Measurements of precipitation, drain outflow, weir depths and air and soil temperatures were carried out hourly. Groundwater levels were measured and samples of drain outflow for analyses were collected twice a month. Mineral N contents in soil were measured three times a year and grain yields and N uptake in crops after harvest.     

Controlled drainage — effects on drain outflow and water quality

A field experimental project was set up in southern Sweden to assess the effects of controlled drainage on hydrology and environment. Controlled drainage makes it possible to vary the drainage intensity with the variation in drainage requirement during season by controlling the height of a riser in the drain outlet and thus to a certain degree control the amount of outflow of solutes via the drainage system. During periods with low drainage demand, the riser in the drain outlet can be raised and the groundwater level in field will rise up to the level of the riser before the discharge takes place. Three plots, each with an area of 0.2 ha (40 m×50 m) were installed on a loamy sand. One plot was drained by conventional subsurface drainage (CD) and two plots were drained by controlled drainage (CWT). The plots contained four lateral drain tubes, at 10 m spacing and placed at 1 m depth. Each plot was isolated by a double layer of plastic sheeting placed in the back-filled trenches to a depth of 1.6 m to prevent lateral leakage and subsurface interactions. Measurements of precipitation, drain outflow and soil and air temperatures were carried out hourly. Groundwater levels were measured and samples of drain outflow were collected twice a month for nitrogen and phosphorous analyses. Mineral nitrogen contents in soil were measured three times a year.Controlled drainage had a significant hydrological and environmental effect during the 2 years of measurement (1996–1998). Compared with CD, the total drain outflow from CWT was 79% less in Year 1 and 94% in Year 2. The total reduction in nitrate losses with CWT corresponded to the reduced outflow rates. Compared with CD, the total amounts of nitrate in drain outflow were 78% less in Year 1 and 94% in Year 2. The highest concentrations of nitrate were measured at the time of the largest outflow rates. The phosphorous losses were 58% less for CWT as compared to the CD values in Year 1 and 85% less in Year 2. The reduction in nitrogen content in the soil profile during the winter season was 60–70% less in CWT than in CD.     

Shallow subsurface drainage in an irrigated vertisol with a perched water table

Waterlogging and salinity are reducing the productivity of irrigated agriculture on clay soils in south east Australia. We compared five drainage treatments: (1) undrained control (Control); (2) mole drains (Mole); (3) mole drains formed beneath gypsum-enriched slots (GES) (Mole + GES); (4) shallow pipe drains installed beneath GES (Shallow Pipe); (5) deep pipe drains (Deep Pipe). The experiment was set out on a vertisol and our measurements were made during the growth of an irrigated onion crop.

Over the 3 months before the spring irrigations commenced, the perched water table on the Control was less than 400 mm below the soil surface for 27% of the time, whereas the shallow drainage treatments (Treatments 2, 3 and 4) reduced this time to less than 4%. During the irrigation season, the perched water table on the Mole + GES treatment rose above 400 mm for 3% of the time. The perched water table on the Mole treatment was above 400 mm for 14% of the time, compared with 19% of the time on the Control. The Deep Pipes were less effective in reducing the depth to the perched water table, both before and during the irrigation period.

Mole drains increased the gas-filled porosity above the drains. However, the gas-filled porosity remained below reported levels for optimum root growth. Although the drains effectively drained excess water, and lowered the water table, the hydraulic gradient was insufficient to remove all of water from the macropores. Gypsum enriched slots above the mole drains increased the gas-filled porosity in the slots but the drainable porosity in the undisturbed soil appeared to be inadequate for optimum root growth, even though some drainage occurred near the slots.

Discharge from the shallow drainage treatments averaged 58 mm for each irrigation, and was considerably more than the amount required to drain the macropores. The mole channels were in reasonably good condition at the end of the irrigation season, with at least 70% of the cross-sectional area of the channel open.

Shallow subsurface drains increased onion yield by about 38%. For each day the water table was above 400 mm, the yield declined by 0.23 tonnes per hectare. Farmer adoption of shallow subsurface drainage will depend on the long-term economic benefits (influenced by the longevity of the mole channels and yields response) and the need to develop more sustainable management practices.     

Detecting subsurface drainage systems and estimating drain spacing in intensively managed agricultural landscapes

Detailed location maps of tile drains in the Midwestern United States are generally not available, as the tile lines in these areas were laid more than 75 years ago. The objective of this study is to map individual tile drains and estimate drain spacing using a combination of GIS-based analysis of land cover, soil and topography data, and analysis of high resolution aerial photographs to within the Hoagland watershed in west-central Indiana. A decision tree classifier model was used to classify the watershed into potentially drained and undrained areas using land cover, soil drainage class, and surface slope data sets. After masking out the potential undrained areas from the aerial image, image processing techniques such as the first-difference horizontal and vertical edge enhance filters, and density slice classification were used to create a detailed tile location map of the watershed. Drain spacings in different parts of the watershed were estimated from the watershed tile line map. The decision tree identified 79% of the watershed as potential tile drained area while the image processing techniques predicted artificial subsurface drainage in approximately 50% of the Hoagland watershed. Drain spacing inferred from classified aerial image vary between 17 and 80 m. Comparison of estimated tile drained areas from aerial image analysis shows a close agreement with estimated tile drained areas from previous studies (50% versus 46% drained area) which were based on GIS analysis and National Resource Inventory survey. Due to lack of sufficient field data, the results from this analysis could not be validated with observed tile line locations. In general, the techniques used for mapping tile lines gave reasonable results and are useful to detect drainage extent from aerial image in large areas. These techniques, however, do not yield precise maps of the systems for individual fields and may not accurately estimate the extent of tile drainage in the presence of crop residue in agricultural fields and/or existence of other spatial features with similar spectral response as tile drains.     

Simulated effect of drainage water management operational strategy on hydrology and crop yield for Drummer soil in the Midwestern United States

The hypothetical effects of drainage water management operational strategy on hydrology and crop yield at the Purdue University Water Quality Field Station (WQFS) were simulated using DRAINMOD, a field-scale hydrologic model. The WQFS has forty-eight cropping system treatment plots with 10 m drain spacing. Drain flow observations from a subset of the treatment plots with continuous corn (Zea mays L.) were used to calibrate the model, which was then used to develop an operational strategy for drainage water management. The chosen dates of raising and lowering the outlet during the crop period were 10 and 85 days after planting, respectively, with a control height of 50 cm above the drain (40 cm from the surface). The potential effects of this operational strategy on hydrology and corn yield were simulated over a period of 15 years from 1991 to 2005. On average, the predicted annual drain flows were reduced by 60% (statistically significant at 95% level). This is the most significant benefit of drainage water management since it may reduce the nitrate load to the receiving streams. About 68% of the reduced drain flow contributed to an increase in seepage. Drainage water management increased the average surface runoff by about 85% and slightly decreased the relative yield of corn crop by 0.5% (both are not statistically significant at 95% level). On average, the relative yield due to wet stress (RYw) decreased by 1.3% while relative yield due to dry stress (RYd) increased by 1%. Overall, the relative crop yield increased in 5 years (within a range of 0.8-6.9%), decreased in 8 years (within a range of 0.2-5.5%), and was not affected in the remaining 2 years. With simulated drainage water management, the water table rose above the conventional drainage level during both the winter and the crop periods in all years (except 2002 crop season). The annual maximum winter period rise ranged between 47 cm (1995) and 87 cm (1992), and the annual maximum crop period rise ranged between no effect (2002) and 47 cm (1993).     

Pipe drainage in the Eastern Padano-Veneta plain in north-east Italy

A survey has been carried out in three Regions of north-eastItaly, Emilia Romagna, Veneto and Friuli Venezia Giulia, withfour objectives: (a) to update the statistics on the use of pipedrainage; (b) to describe the farms that adopt this technique asa replacement of the traditional surface drainage methods;(c) to characterise the features of the drained soils and of thedrainage systems, and (d) to assess their performance. Withalmost 70.000 ha drained, the Regions present almost all of thepipe drained area in Italy. Pipe drainage first saw applicationsin the last seventies and became increasingly popular during theeighties. Most pipe drainage systems are installed in heavysoils, where the underground waterlogging is due to seasonalperched water table or to infiltrations from rivers or sea. Due tothe pedoclimatic variability of the area, slightly differentsolutions in terms of design variables and installation criteriaare found, but the following features are quite common: drainspacing 11–13 m slope 0.1–0.3%, depth 0.9–1 m. The pipe drains discharge in open collectors (single systems). Anincreasing interest for the use of the drainage systems forsubirrigation purposes has been observed, particularly inVeneto, requiring some adjustment in the drainage design. Theperformance of drainage in terms of control of water tabledepth and maintenance requirements are considered satisfactoryin almost all the cases. The most effective solutions forsuccessfully managing the subirrigation are also described.The introduction of pipe drains allows to enlarge fields (to morethan 10 has) and to save time for carrying out the operations forcrop cultivation. The crop yield in pipe drained fields is slightly higherto that obtained in the traditionally drained fields, withthe exception of winter wheat.     

Field evaluation of sand-ditch water harvesting technique in Jordan

Water harvesting is viable alternatives for rainfed agricultural production in semiarid lands. A field experiment was conducted to evaluate the efficiency of a relatively new water harvesting technique, called sand ditch, for moisture and soil conservation. Twelve field plots of 10 m × 2 m were constructed in two adjacent fields having silt loam soils but varied in soil depth, 0.75 m and 2 m, and slope of 10% and 12%. A 130 L barrel was installed at the downslope end of the plots to collect water and sediments at the end of each rainstorm along the rainy season. Three types of treatments were used in duplicates (12 plots in total); sand-ditch plots in which a ditch of 2-m long, 1 m wide and 0.8 m deep was constructed in the middle of plots across the slope (2 in each field), two compacted plots and two plots covered with plastic mulch in addition to four control plots, 2 in each field. The total amount of runoff, sediment concentration, total infiltration and sediment loss for the experimental plots were measured or calculated after each storm during the winter season 2004/2005. Experimental results showed that sand-ditch technique significantly reduced runoff and sediment loss and increased infiltration and soil moisture compared to control or compacted plots. The overall average runoff and sediment reductions in the sand-ditch plots were 46% and 61% compared to control plots. Sediment losses from compacted plots were about 2.2 and 6 folds higher than control and sand-ditch plots, respectively making soil compaction unsuitable technique for rainfall harvesting under the current experimental and climatic conditions. Construction of sand ditch also increased the dry matter yield of native grass by an average of 62% and 40% in the two experimental fields compared to control.     

Response of wheat to saline irrigation and drainage

The response of wheat (Triticum aestiuum L.) to varying depths of irrigation, quantity of water applied and to the drainage conditions was studied in 2 m × 2 m × 2 m size lysimeters filled in with a sandy loam soil. Saline water with an electrical conductivity of 8.6 dS m⁻¹ was used for irrigation. The treatments included four irrigations of 5 cm depth, four irrigations of 7 cm, and three irrigations of 9 cm, scheduled on the basis of cumulative pan evaporation, while the drainage conditions were represented by the drained and undrained lysimeters. Another treatment, using good quality water for irrigation, represented the potential yield of the crop. The growth parameters, as well as the yield, showed an improvement with larger irrigation depth increments in the drained lysimeters. But, in contrast, in the undrained lysimeters, the yield was reduced with larger irrigation depth increments, mainly due to a sharp rise in water table depth during the irrigation cycles. The rise and fall in water table showed a high sensitivity and were also highly disproportionate to the irrigation and evapotranspiration events. The yield tended to be higher with a smaller depth of water applied more frequently in the undrained lysimeters. But, in view of the limitations of conventional surface irrigation to apply water in smaller depth increments, an improved drainage is imperative for cropping in shallow saline water table conditions.     

Drainage and desalinization of heavy clay soil in Portugal

The Leziria Grande area consists mainly of poorly drained, saline clay soils of marine origin. Three experimental fields were laid out to find whether subsurface drainage can be effective in lowering the groundwater table and improving desalinization.Subsurface drainage results in a lower groundwater table than does surface drainage. With increasing spacing, the groundwater remains at a higher level for longer periods, which is expressed here by the sum of exceedances of the groundwater table above 30 cm during winter.Soil salinity, expressed as EC_1:2, and sodicity, expressed as E.S.P., decreased during the first 3 years, in which precipitation varied between 600 and 750 mm and the average drain outflow was about 250 mm. The leaching efficiency decreased with time, indicating that the removal of salt is a slow process in fine-textured soil.Application of gypsum lowered the E.S.P. The infiltration rate and the drain outflow increased. Although the total amount of salts in the drainwater was 40% higher than for the untreated plots, no lower EC_1:2 values were found. This is ascribed to spatial variability in soil salinity.     

Simulation of nitrate-N movement in southern Ontario,Canada with DRAINMOD-N

DRAINMOD-N, a mathematical model to predict nitrate-N concentrations in surface runoff and drain outflows from subsurface-drained farmlands, has been tested against field data collected in southern Ontario. The data was collected in a corn field from 16 conventional drainage and subirrigation plots in Woodslee, Ontario, from 1992 to 1994. The model performance was evaluated by comparing the observed and simulated nitrate-N concentrations in surface runoff and drain outflows. A precise calculation of water-table depth is an essential prerequisite for a model to obtain a proper prediction of nitrate-N movement. For the simulation of water-table depth, the lowest root mean square error and the highest correlation coefficient of linear regression were 173 mm and 0.51 for the subirrigation plots; and 178 mm and 0.84 for the subsurface drainage plots. Therefore, the performance of DRAINMOD-N for soil hydrologic simulations was satisfactory and it could be used for assessing nitrogen fate and transport. For the simulation of nitrate-N losses in the subirrigation plots, the lowest root mean square error and the highest correlation coefficient of linear regression were 0.74 kg/ha and 0.98 for surface runoff; and 6.53 kg/ha and 0.91 for drain outflow. For the simulation in the subsurface drainage plots, the lowest root mean square error and the highest correlation coefficient of linear regression were 0.70 kg/ha and 0.96 for surface runoff; and 6.91 kg/ha and 0.92 for drain outflow. The results show that DRAINMOD-N can perform satisfactory simulation of soil hydrology and nitrate-N losses in surface runoff under various water-table management practices. The model can, therefore, be used to evaluate different water pollution scenarios and help in the development and testing of various pollution control strategies for fields in cold weather such as that in southern Canada.     

Characteristics of water reuse and its effects on paddy irrigation system water balance and the riceland ecosystem

Rapid industrial development in the rice-growing regions has increased competition for the scarce water resources. Water reuse (surface and subsurface agriculture drainage water, storm runoff, sewerage effluent and industrial wastewater recycling) is in widespread use as a method of supplementing the paddy water supply, therefore, there is a need to clarify its effects on the paddy system water balance and riceland ecosystem. Field data and simulation results from a complex runoff model (created on a daily basis), were used to estimate the water balance and assess the effects on the irrigation system of a water shortage area in Niigata Prefecture, Japan. For three years (1991–1993), the average water reuse component was within the range 14∼ 15% of the total irrigation water supply. Apart from meeting the water needs at peak demand periods, water reuse is a quick-response water supply solution during dry spells, increasing both the water reliability and crop security. To understand the impact of water reuse on the riceland ecosystem, its effect on total phosphorus (T-P), total nitrogen (T-N), suspended solids (SS), and chemical oxygen demand (COD) was assessed. Blending of the drainage water was done to reduce the irrigation water concentrations, to approximate the traditional dual canal system and to increase farmer satisfaction with the water reuse system. Apart from the fact that the amount of return flow drained out of the irrigation system was reduced when drainage water was reused for irrigation, the effluent load reductions for SS and T-P owing to water reuse were consistently high. Hence, water reuse not only helps meet irrigation water needs, but also aids purification of the agricultural drainage water and preservation of the riceland ecosystem.     

Time-dependent drainage from root zone and drainage coefficient under different irrigation management levels for subsurface drainage design in Egypt

Drainage water from the lower boundary of the root zone is an important factor in the irrigated agricultural lands for prediction of the water table behavior and understanding and modeling of water and chemical movement in the soil profile. The drainage coefficient is an important parameter for the design of subsurface drainage. On a 33,138 ha of the Nile Delta in Egypt, this study is conducted using 90 irrigation periods over a 3-year crop rotation to estimate the time-dependent drainage from the root zone and the design subsurface drainage coefficient with different cropping seasons and irrigation management levels.The results showed that the cropping seasons and the irrigation management levels as indicated by different irrigation efficiency are significantly affected the drainage rate from the root zone and the design value of subsurface drainage coefficient. Drainage rates from the root zone of 1.72 mm/d and 0.82 mm/d were estimated for summer and winter seasons, respectively. These rates significantly decreased in a range of 46% to 92% during summer season and 60% to 98% during winter season when the irrigation efficiency is increased in a range of 5% to 15%. The subsurface drainage coefficient was estimated to be 1.09 mm/d whereas the design drain pipe capacity was estimated to be 2.2 mm/d, based on the peak discharge of the most critical crop (maize), rather than 4.0 mm/d which is currently used. A significant decrease of the drainage coefficient and the drain pipe capacity ranges from 18% to 45% was found with the increase of irrigation efficiency in a range of 5% to 15%. The leaching requirement for each crop was also estimated.     

深圳水库污水截排工程规模的选择

在如何选定污水截排工程的截排规模上，分析了套用市政排水截流倍数或选取某频率洪峰流量来确定截排流量的方法的不足，结合水库水质以面源污染为主的特征，采用综合选择方法——即推求典型年降雨所形成的全年逐时径流过程和全年径流量，计算各截排流量下的截排水量，通过水库水质模型，根据各截排流量对应未截排水量所携带的入库污染负荷量，建立截排流量与水库水质的关系，最终选定符合水库水质标准的截排流量为工程规模。     

Efficiency of controlled drainage and subirrigation in reducing nitrogen losses from agricultural fields

In northeast Italy, a regimen of controlled drainage in winter and subirrigation in summer was tested as a strategy for continuous water table management with the benefits of optimizing water use and reducing unnecessary drainage and nitrogen losses from agricultural fields.To study the feasibility and performance of water table management, an experimental facility was set up in 1996 to reproduce a hypothetical 6-ha agricultural basin with different land drainage systems existing in the region. Four treatments were compared: open ditches with free drainage and no irrigation (O), open ditches with controlled drainage and subirrigation (O-CI), subsurface corrugated drains with free drainage and no irrigation (S), subsurface corrugated drains with controlled drainage and subirrigation (S-CI). As typically in the region free drainage ditches were spaced 30 m apart, and subsurface corrugated drains were spaced 8 m apart.Data were collected from 1997 to 2003 on water table depth, drained volume, nitrate-nitrogen concentration in the drainage water, and nitrate-nitrogen concentration in the groundwater at various depths up to 3 m.Subsurface corrugated drains with free drainage (S) gave the highest measured drainage volume of the four regimes, discharging, on average, more than 50% of annual rainfall, the second-highest concentration of nitrate-nitrogen in the drainage water, and the highest nitrate-nitrogen losses at 236 k ha⁻¹.Open ditches with free drainage (O) showed 18% drainage return of rainfall, relatively low concentration of nitrate-nitrogen in the drainage water, the highest nitrate-nitrogen concentration in the shallow groundwater, and 51 kg ha⁻¹ nitrate-nitrogen losses.Both treatments with controlled drainage and subirrigation (O-CI and S-CI) showed annual rainfall drainage of approximately 10%. O-CI showed the lowest nitrate-nitrogen concentration in the drainage water, and the lowest nitrogen losses (15 kg ha⁻¹). S-CI showed the highest nitrate-nitrogen concentration in the drainage water, and 70 kg ha⁻¹ nitrate-nitrogen losses. Reduced drained volumes resulted from the combined effects of reduced peak flow and reduced number of days with drainage.A linear relationship between daily cumulative nitrate-nitrogen losses and daily cumulative drainage volumes was found, with slopes of 0.16, 0.12, 0.07, and 0.04 kg ha⁻¹ of nitrate-nitrogen lost per mm of drained water in S-CI, S, O, and O-CI respectively.These data suggest that controlled drainage and subirrigation can be applied at farm scale in northeast Italy, with advantages for water conservation.     

基于DRAINMOD模型的不同灌排模式稻田水氮运移模拟

[目的]研究不同灌排模式稻田水氮动态变化,为南方稻作区节水减排提供科学依据.[方法]基于实测的田间灌排水量及氮素变化数据,采用Morris方法检测DRAINMOD模型水氮运移相关参数的灵敏度,并利用DRAINMOD模型对传统灌排模式和控制灌排模式下稻田水氮动态进行模拟.[结果]20～40 cm 土层侧向饱和导水率对稻田...     

Seasonal water balance of an Ozark hillslope

Analysis of field water balance components provides information necessary to minimize the risk of offsite movement of contaminants from crop production practices or animal manure applications. The objective of this study was to determine the timing and amount of surface runoff and drainage from the root zone for a hillslope in the Ozark Highlands of US. A 0.4 ha watershed with slopes of 8–20% having tall fescue (Festuca arundinacea Schreb.) cover was established in northwestern Arkansas (35°56′W, 93°51′N). Continuous measurements of water balance parameters were made from June 1997 to August 1998. Soil water drainage was estimated as the residual of weekly water balance calculations. Runoff occurred in response to three precipitation events in the winter of 1998 and totaled 30.6 mm of water or 2.6% of the 1185 mm of precipitation that fell at the site during the study period. Storms of comparable or greater intensity during other seasons failed to produce runoff, a result that was likely due to dry soil conditions and taller grass canopy. Drainage through the root zone totaled 117 mm and occurred primarily during an 83-day interval in the winter of 1998. The water balance was dominated by evaporation, which accounted for 91% (1080 mm) of the precipitation. Tall fescue was capable of sustaining relatively high evaporation rates between infrequent summer rains thereby dewatering the soil profile, which was not replenished until winter. Delaying spring animal manure applications in the Ozarks until evaporation has increased and the soil profile has begun to dry would decrease the risk of offsite transport of potential contaminants contained in the manure.