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1.
Available water holding capacity (AWC) and field capacity (FC) maps have been produced using regression models of high resolution apparent electrical conductivity (ECa) data against AWC (adj. R2 = 0.76) and FC (adj. R2 = 0.77). A daily time step has been added to field capacity maps to spatially predict soil water status on any day using data obtained from a wireless soil moisture sensing network which transmitted hourly logged data from embedded time domain transmission (TDT) sensors in ECa-defined management zones. In addition, regular time domain reflectometry (TDR) monitoring of 50 positions in the study area was used to assess spatial variability within each zone and overall temporal stability of soil moisture patterns. Spatial variability of soil moisture within each zone at any one time was significant (coefficient of variation [% CV] of volumetric soil moisture content (θ) = 3-16%), while temporal stability of this pattern was moderate to strong (bivariate correlation, R = 0.52-0.95), suggesting an intrinsic soil and topographic control. Therefore, predictive ability of this method for spatial characterisation of soil water status, at this site, was limited by the ability of the sensor network to account for the spatial variability of the soil moisture pattern within each zone. Significant variability of soil moisture within each ECa-defined zone is thought to be due to the variable nature of the young alluvial soils at this site, as well as micro-topographic effects on water movement, such as low-lying ponding areas. In summary, this paper develops a method for predicting daily soil water status in ECa-defined zones; digital information available for uploading to a software-controlled automated variable rate irrigation system with the aim of improved water use efficiency. Accuracy of prediction is determined by the extent to which spatial variability is predicted within as well as between ECa-defined zones.  相似文献   

2.
Potato production accounts for ∼24% of the cultivated land-use in Prince Edward Island, Canada. The island often experiences prolonged dry periods interspersed with excessive rainfall events throughout the growing season. Thus, water retention is important for maximum crop production while sediment and nutrient loading to surface water systems are also concerns. Therefore, agronomic practices that reduce the environmental impact of potato production are being sought. Basin tillage (BT) is a potential option in which small dams are created in the furrows (row middles), resulting in basins that enhance infiltration, reduce runoff, minimize contaminant loads, and increase yields.This on-farm study compared BT against two types of ‘conventional’ hilling treatments with replicated plots on four field sites over two growing seasons. Field sites had sandy loam soils with topography slopes ranging from 3% to 5%. Within each field, nine 25 m long and 3.66 m wide (4 rows) plots were established, including three plots of each hilling treatment (CT = conventional tillage; RS = row shaper tillage; BT = basin tillage). Runoff volume, nutrient (phosphate, ammonium, nitrate) and suspended solids loads were measured using collection barrels on the down slope end of each furrow.Basin tillage had 78% and 75% less runoff than CT and RS, respectively (P < 0.05). Runoff differences between BT and CT were significant at all sites while runoff differences between BT and RS were significant at three of four sites. Reductions for each parameter (on a mass basis) averaged across all sites were: sediment 89%, nitrate 45%, ammonium 38%, and phosphate 15%; although, treatment effect was not significant for some mass loads in some fields. No significant effect on marketable potato yield was observed at any site; soil water was not limiting in either growing season. Overall, basin tillage was effective at reducing runoff and nutrient losses without affecting yield and appears to be an effective tool for decreasing environmental risks.  相似文献   

3.
The newly developed SoilClim model is introduced as a tool for estimates of reference (ETo) and actual (ETa) evapotranspiration, presence of snow cover, soil temperature at 0.5 m depth and the soil moisture course within two defined layers. It enables one to determine the soil moisture and temperature regimes according to the United States Department of Agriculture (USDA) soil taxonomy. SoilClim works with daily time steps and requires maximum and minimum air temperature, global solar radiation, precipitation, vapor pressure and wind speed as meteorological inputs as well as basic information about the soil properties and vegetation cover. The behavior of SoilClim was assessed using observations at 5 stations in central Europe and 15 stations in the central U.S. The modeled ETo was compared with atmometers so that the coefficient of determination (R2) was 0.91 and root mean square error (RMSE) was 0.53 mm. The estimated ETa was compared against eddy-covariance and Bowen ratio measurements (R2 varied from 0.74 to 0.80; RMSE varied from 0.49 to 0.58 mm). The soil temperature (at 0.5 m depth) was estimated with good accuracy (R2 varied from 0.94 to 0.97; RMSE varied from 1.23 °C to 2.95 °C). The ability of the SoilClim model to mimic the observed soil water dynamics was carefully investigated (relative root mean square error rRMSE varied from 2.8% to 34.0%). The analysis conducted showed that SoilClim gives reasonable estimates of evaluated parameters at a majority of the included stations. Finally, a spatial analysis of soil moisture and temperature regimes (according to USDA) within the region of the Czech Republic and the northern part of Austria under present conditions was conducted and diagnosed the appearance of Perudic, Subhumid Udic, Dry Tempudic (the highest frequency), Wet Tempustic and Typic Tempustic. The simulated mean soil temperature (0.5 m depth) varied from less than 7.0 °C to 11.0 °C throughout this region. Based on these results, the SoilClim model is a useful and suitable tool for water balance and soil climate assessment on local and regional scales.  相似文献   

4.
Soil water supply is the main limiting factor to crop production across the Loess Plateau, China. A 2-year field experiment was conducted at the Changwu agro-ecosystem research station to evaluate various water management practices for achieving favorable grain yield (GY) with high water use efficiency (WUE) of spring maize (Zea mays L.). Four practices were examined: a rain-fed (RF) system as the control; supplementary irrigation (SI); film mulching (FM); and straw mulching (SM) (in 2008 only). The soil profile water storage (W) and the crop evapotranspiration (ET) levels were studied during the maize growing season, and the GY as well as the WUE were also compared. The results showed that mean soil water storage in the top 200 cm of the profile was significantly (P < 0.05) increased in the SI (380 mm in 2007, 411 mm in 2008) and SM (414 mm in 2008) compared to the FM (361 mm in 2007, 381 mm in 2008) and RF (360 mm in 2007, 384 mm in 2008) treatments. The soil water content was lower at the end of growing season than before planting in the 60-140 cm part of the profile in both the RF and FM treatments. Cumulative ET and average crop coefficiency (Kc) throughout the whole maize growing season were significantly (P < 0.05) higher in the SI (ET, 501 mm in 2007, 431 mm in 2008; Kc, 1.0 in 2007, 0.9 in 2008) treatment than in the other treatments. Both FM and SI significantly improved the GY. The WUE were increased significantly (23-25%; P < 0.05) under the FM treatment. It was concluded that both SI and FM are beneficial for improving the yield of spring maize on the Loess Plateau. However, FM is preferable because of the shortage of available water in the area.  相似文献   

5.
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.  相似文献   

6.
Northeast Thailand has a semi-humid tropical climate which is characterized by dry and rainy seasons. In order to stabilize crop production, it may be necessary to develop new water resources, such as soil moisture and groundwater, instead of rainfed resources. This is because rainfed agriculture has already been unsuccessfully tried in many areas of this region. In this study, we investigate the soil water content in rainfed fields in Khon Kaen in Northeast Thailand, where rice and sugarcane were planted, over a 1-year period that contained both dry and rainy seasons, and estimate the actual evapotranspiration (ETa) using micrometeorological data. In addition, we assess the water balance from the results of the soil water content investigation and the actual evapotranspiration. Although the soil water content at depths above 0.6 m in both the lower and the sloping fields gradually decreased during the dry season, the soil water content at a depth of 1.0 m was under almost constant wet conditions. Two-dimensional profiles of the soil water content demonstrated that at the end of the dry season, the soil layers below a depth of 0.4 m showed a soil water content of more than 0.10-0.15 m3 m−3, thus suggesting that water was supplied to the sugarcane from those layers. The range in ETa rates was almost the same as that in the previous study. The average ETa rates were 3.7 mm d−1 for the lower field and 4.2 mm d−1 for the sloping field. In the dry season, an upward water flow of 373 mm (equivalent to a flux of 1.9 mm d−1) was estimated from outside the profile. The source of this upward water flow was the sandy clay (SC) layer below a depth of 1 m. It was this soil water supply from the SC layer that allowed the sugarcane to grow without irrigation.  相似文献   

7.
The purpose of this study was to estimate precipitation (P), reference evapotranspiration (ETo), precipitation deficit (PD = P − ETo) and relative crop yield reduction (YR) for a generic crop under climate change conditions for three locations in Puerto Rico: Adjuntas, Mayagüez, and Lajas. Reference evapotranspiration was estimated by the Penman-Monteith method. Precipitation and temperature data were statistically downscaled and evaluated using the DOE/NCAR PCM global circulation model projections for the B1 (low), A2 (mid-high) and A1fi (high) emission scenarios of the Intergovernmental Panel on Climate Change Special Report on Emission Scenarios. Relative crop yield reduction was estimated from a water stress factor, which is a function of soil moisture content. Average soil moisture content for the three locations was determined by means of a simple water balance approach.Results from the analysis indicate that the rainy season will become wetter and the dry season will become drier. The 20-year average September precipitation excess (i.e., PD > 0) increased for all scenarios and locations from 121 to 321 mm between 2000 and 2090. Conversely, the 20-year average February precipitation deficit (i.e., PD < 0) changed from −27 to −77 mm between 2000 and 2090. The results suggest that additional water could be saved during the wet months to offset increased irrigation requirements during the dry months. The 20-year average relative crop yield reduction for all scenarios decreased on average from 12% to 6% between 2000 and 2090 during September, but increased on average from 51% to 64% during February. Information related to the components of the hydrologic water budget (i.e., actual evapotranspiration, surface runoff, aquifer recharge and soil moisture storage) is also presented. This study provides important information that may be useful for future water resource planning in Puerto Rico.  相似文献   

8.
The hydraulics of pitcher irrigation in saline water condition was studied in laboratory conditions in terms of flow behaviour of pitcher, soil moisture distribution, wetting front advance and distribution of salt concentration in the soil using different pitcher making materials. The Pitcher Type 1 (PT1) made up of local soil and sand yielded the lowest mean hourly depletion ranging from 0.42 to 0.62% depending on salinity of the water used. It was followed by PT2 made up of local soil, sand and resinous material with a mean hourly depletion of 0.51-0.69% and PT3 with local soil, saw dust and sand with a mean hourly depletion of 0.91-1.02%. In all cases, with the increase in salinity level of the water used (ranging from 5 to 20 dS/m), the depletion rate and moisture content in the soil profile were found to decrease.Similarly, it was found that PT1 yielded the lowest wetting front advance and salt movement followed by PT2 and PT3. It was observed that the wetting front advance in the soil decreased with increasing salinity level of the water. The salt concentration in the soil was minimum near the pitcher and maximum at the soil surface and periphery of the wetted zone. In case of PT1, the maximum salt concentration in the soil profile ranged between 1.09 and 3.88 dS/m using water with a salinity ranging from 5 to 20 dS/m, respectively. Similarly, for PT2 the maximum salt concentration in the soil profile also ranged from 1.09 to 3.88 dS/m and for PT3 from 2.30 to 6.07 dS/m. A paired t-test revealed that the moisture as well as the salt distribution of PT3 differed significantly from PT1 and PT2 at α = 0.05. Even, if the salt concentration remained the same and the moisture content remained within field capacity for PT1 and PT2, PT1 is preferred in comparison to PT2 and PT3 as the pitcher material of PT1 is locally economically available.  相似文献   

9.
Micro-catchment water harvesting (MCWH) requires development of small structures across mild land slopes, which capture overland flow and store it in soil profile for subsequent plant uses. Water availability to plants depends on the micro-catchment runoff yield and water storage capacity of both the plant basin and the soil profile in the plant root zone. This study assessed the MCWH potential of a Mediterranean arid environment by using runoff micro-catchment and soil water balance approaches. Average annual rainfall and evapotranspiration of the studied environment were estimated as 111 and 1671 mm, respectively. This environment hardly supports vegetation without supplementary water. During the study period, the annual rain was 158 mm in year 2004/2005, 45 mm in year 2005/2006 and 127 mm in year 2006/2007. About 5000 MCWH basins were developed for shrub raising on a land slope between 2 and 5% by using three different techniques. Runoff at the outlets of 26 micro-catchments with catchment areas between 13 and 50 m2 was measured. Also the runoff was indirectly assessed for another 40 micro-catchments by using soil water balance in the micro-catchments and the plant basins. Results show that runoff yield varied between 5 and 187 m3 ha−1 for various rainfall events. It was between 5 and 85% of the incidental rainfall with an average value of 30%. The rainfall threshold for runoff generation was estimated about 4 mm. Overall; the soil water balance approach predicted 38-57% less water than micro-catchment runoff approach. This difference was due to the reason that the micro-catchment runoff approach accounted for entire event runoff in the tanks; thus showed a maximum water harvesting potential of the micro-catchments. Soil water balance approach estimated water storage in soil profile and did not incorporate water losses through spillage from plant basins and deep percolation. Therefore, this method depicted water storage capacity of the plant basins and the root zone soil profile. The different between maximum water harvesting potential and soil-water storage capacity is surplus runoff that can be better utilized through appropriate MCWH planning.  相似文献   

10.
The effect of moisture tension and doses of phosphate fertilization on yield components of sweet corn A-7573 (Zea mays L.) hybrid, in a Calcium Vertisol were evaluated. Four levels of soil moisture tension, ranging from −5 to −80 kPa, and three levels of phosphate fertilization: 60, 80, and 100 kg ha−1 were studied. In order to evaluate the effect of the experimental treatments, plant growth, development, and yield were monitored. Treatments were distributed using the randomized complete block design (RCB) for divided plots of experimental units. ANOVA analysis indicated that the effects on more humid treatments (−5 and −30 kPa) were statistically equivalent, however were different from the effect of −55 kPa treatment, which in turn was statistically different from the effect of the driest treatment (p ≤ 0.01). On the other hand, 80 and 100 kg ha−1 phosphate doses were statistically equal among them, but different from the lowest dose in almost all cases (p ≤ 0.01), which suggests that 80 kg ha−1 P2O5 application is sufficient to satisfy the nutritional requirements of the A-7573 hybrid. Both stress caused by the lack of water and the one due to deficiency of phosphorus affect all variables under study, however none of them showed interaction between irrigation and fertilization treatments. Irrigation of sweet corn crop is advisable when soil moisture tension grows to −30 kPa at 0-30 cm depth and to apply a phosphate fertilization dose of 80 kg ha−1 is also recommended; using this management, sweet corn expected average length and fresh weight are 30.8 cm and 298 g, respectively, and their average yield is around 16.5 t ha−1. In accordance with regression equations obtained, the maximum values in the evaluated response variables are obtained for a rank from −14.4 to −22.2 kPa in soil moisture tension. The greater efficiency in the use of irrigation water for sweet corn was of 36 kg ha−1 for every millimetre laminate of watering applied, found in the −30 kPa treatment of soil moisture tension.  相似文献   

11.
The amount of soil water at the beginning of the growing season has a large impact on crop yields in rainfed agriculture, especially in semi-arid regions and in years with below-average rainfall in more humid climates. Robust algorithms are needed to estimate soil water storage before planting to aid crop management decisions. The main objectives of this paper are to investigate soil water recharge during the non-growing season (October 20 to May 1) in a semi-arid, temperate ecosystem in south-central Nebraska (USA) and to evaluate empirical models to estimate soil water content at the beginning of the summer-crop growing season. A database of soil water content measurements collected over 5 years at nine locations in south-central Nebraska was used to estimate available water-holding limits in the soil profile and to determine the change in available soil water during the non-growing season. Regression analysis was performed to analyze the relationship among soil water recharge, residual soil water (i.e., soil water content at the end of the previous growing season), total precipitation, and available water-holding capacity (AWHC) in the root zone to 1.5 m. Precipitation storage efficiency (PSE) was calculated as the quotient of soil water recharge and total non-growing season precipitation. Predictive models to estimate soil water content at the beginning of summer-crop growing season were derived from these analyses. A large portion of the variation in soil water recharge was explained by residual soil water and precipitation. PSE averaged 28% across site-years; low PSE values were associated with high residual soil water and/or low AWHC. Two predictive models (linear and linear-plateau) that used residual soil water, total precipitation, and AWHC as independent variables explained 75-80% of the variation in the measured soil water content at the beginning of the summer-crop growing season. These empirical models represent a new tool to estimate soil water content by planting date of summer crops. Site-management conditions such as residue amount and its architecture, tillage system, soil texture, and terrain slope are not currently accounted for in these models and would likely improve predictive capacity.  相似文献   

12.
Paddy fields are characterized by standing water and saturation condition during the entire crop growth period. However, in sub-humid and semi-arid areas, scarce rainfall and intermittent dry spells often cause soil moisture depletion resulting in unsaturated condition in the fields. These distinctive characteristics of the paddy fields have significant influence on the runoff generation and soil moisture retention characteristics of the watershed. In this study, the objective is to extend the application of the Soil Conservation Services Curve Number (SCS-CN)-based models for the geospatial and temporal simulation of soil moisture to paddy field-dominated agricultural watersheds in the water scarce areas. Different SCS-CN-based models, integrated with the soil moisture balance equation, are used to estimate the surface runoff and soil moisture content wherein, the spatial variation in the soil hydraulic characteristics is used to calculate the geospatial variation in soil moisture content. Physical significance of the terms initial abstraction (Ia) and potential maximum retention (S) in these models and their influence on the estimation of runoff and soil moisture are analysed in detail. A new SCS-CN-based model for soil moisture simulation (SCS-CN-SMS), to improve the soil moisture estimation, is proposed in this paper. The proposed model is built up on the soil moisture balance equation to account for the effect of ponding condition and soil moisture variation between the dry and saturation condition. The method is tested with 3 years observed surface runoff data and crop production statistics from a part of the Gandeshwari sub-watershed in West Bengal, India. The entire study area is divided into cells of 20 m × 20 m. Various components of the soil moisture balance equation are estimated for each cell as a function of the soil moisture content. Remote Sensing Technique and Geographic Information System (GIS) are used to extract and integrate the spatially distributed land use and soil characteristics. The Hortonion overland flow concept adopted in the SCS-CN method is used to estimate the soil hydraulic characteristics of each cell in which the curve number is used to infer the spatial variation of the land use and soil characteristics. Even though the original SCS-CN method and the existing modified versions are efficient for runoff estimation, these models are found to be inappropriate for the estimation of soil moisture distribution. On the other hand, the proposed SCS-CN-SMS model gives better results for both runoff and soil moisture simulation and is, therefore, more suitable for the hydrological modeling of paddy field-dominated agricultural watersheds.  相似文献   

13.
Plant growth and development are influenced by weather conditions that also affect water use (WU) and water use efficiency (WUE) and ultimately, yield. The overall goal of this study was to determine the impact of weather and soil moisture conditions on WU and WUE of sweet corn (Zea mays L. var rugosa). An experiment consisting on three planting dates was conducted in 2006 at The University of Georgia, USA. A sweet corn genotype sh2 was planted on March 27 under irrigated and rainfed conditions and on April 10 and 25 under irrigated conditions only. Soil moisture was monitored using PR2 probes. Rainfall and irrigation were recorded with rain gauges installed in the experimental area while other weather variables were recorded with an automatic weather station located nearby. A water balance was used to obtain the crop's daily evapotranspiration (ETc). WUE was calculated as the ratio of fresh and dry matter ear yield and cumulative ETc. The potential soil moisture deficit (Dp) approach was used to determine the crop's moisture stress. Results were analyzed using a single degree freedom contrast, linear regression, and the least significant difference. WU and WUE of sweet corn were both markedly affected by the intra-seasonal weather variability and Dp. For both variables, significant (p < 0.05) differences were found between planting dates under irrigated conditions and between the irrigated and rainfed treatments. WU was as high as 268 mm for the April 10 planting date under irrigated conditions and as low as 122 mm for the March 27 planting date under rainfed conditions. The maximum soil moisture deficit was reached at the milky kernel stage and was as high as 343 mm for the March 27 planting date under rainfed conditions and as low as 260 mm for the April 10 planting date under irrigated conditions. Further work should focus on the impact of the intra-seasonal weather variability and soil moisture conditions during different crop stages to determine critical periods that affect yield.  相似文献   

14.
An application of the FAO56 approach to calculate actual evapotranspiration (AET) and soil moisture is reported, implemented by means of the HIDROMORE computerized tool, which performs spatially distributed calculations of hydrological parameters at watershed scale. The paper describes the application and validation of the model over 1 year in an area located in the central sector of the Duero Basin (Spain), where there is a network of 23 stations for continuous measurement of soil moisture (REMEDHUS; Soil Moisture Measurement Stations Network) distributed over an area of around 1300 km2. The application integrated a series of Landsat 7 ETM+ images of 2002, from which the NDVI series (Normalized Difference Vegetation Index) and the map of land covers/uses were derived. Validation consisted of the use of the REMEDHUS soil moisture series and their comparison with the series resulting from the application. Two simulations were performed, with soil parameters values at the surface (0-5 cm depth) and at the mean of the profile scale (0-100 cm depth). The behaviour of the simulated soil moisture was described by means of its correlation with the measured soil moisture (determination coefficient, R2 = 0.67 for the surface values and 0.81 for the mean profile values), and the Root Mean Square Error (RMSE), resulting in a range of it for the 23 stations between 0.010 and 0.061 cm3 cm−3. The application afforded an underestimation of the soil moisture content, which suggests the need for a redefinition of the limits of the plant available water used in the calculation. The results showed that HIDROMORE is an efficient tool for the characterization of hydrological parameters at global scale in the study zone. The combination of the FAO56 methodology and remote sensing techniques was efficient in the spatially distributed simulation of soil moisture.  相似文献   

15.
This work describes the influence of the application of sugar foam (an organic residue from sugar beet industry) on water retention properties, over an extended period of time (>25 years), in two red soils in the La Mancha region of Spain. The properties of gravimetric moisture at field capacity, gravimetric moisture in the permanent wilting point and available water retention capacity both in the original soil - without the addition of sugar foam - and in the soil affected by the addition of sugar foam are compared. For this purpose, the profiles are characterised macro morphologically. Chemical, physical-chemical and mineralogical parameters are determined, in addition to determining the water retention curves of each soil with tensiometers and Richards pressure plates.The sugar foam applied to the soil altered its physical and chemical properties. An increase in contents of organic matter (3.5% versus 1.4%), calcium carbonate (40.8% versus 0%) and pH (8.2 versus 6.3) are observed in the superficial horizon of the studied soils, although there is no such significant increase in electrical conductivity (0.33 dS/m versus 0.25 dS/m). With regard to the physical properties, the depth of horizon A increases (32 cm versus 12 cm), the stoniness reduces (5% versus 25%), the structure is well developed, due to the texture becomes finer (silty versus sandy clay loam), and, finally, the bulk density reduces (0.79 g cm−3 versus 1.19 g cm−3).The gravimetric moisture at field capacity was 49% in the soil altered with sugar foam, versus 12% in the non-altered soil; the gravimetric moisture in the permanent wilting point was 14.5% versus 8% and the available water retention capacity was 34.5% and 4%, respectively. It can be concluded that the increase of calcium carbonate, organic matter and the reduction of bulk density are the most influential factors in this process. The scientific novelty of this work is that the hydro-behaviour of the soil due to the addition of sugar foam improves the characteristic values of moisture and, therefore, the agronomical qualities of the soil.  相似文献   

16.
Comparative studies of drainage and leaching under tillage systems in irrigated tropical and sub-tropical Vertisols are sparse. The objective of this study was to quantify drainage under cotton-based cropping systems sown on permanent beds in an irrigated Vertisol. Drainage and soil water storage were measured with the chloride mass balance method and neutron moisture meter, respectively, during the 2002-03, 2004-05, 2006-07 and 2008-09 cotton seasons in an on-going experiment in a Vertisol in NW NSW. The experimental treatments were: cotton monoculture sown either after conventional tillage or on permanent beds, and a cotton-wheat rotation on permanent beds where the wheat stubble was retained as in situ mulch into which the following cotton crop was sown. Subject to in-crop rainfall, irrigation frequency varied between 7 and 14 days for cotton and 2-3 months for wheat. In 2005, a split-plot design was superimposed on the existing experiment such that the main-plot treatments were irrigation frequency (“frequent”, 7-14-day irrigation interval; “infrequent”, 14-21-day irrigation interval), and sub-plot treatments were the historical tillage system/crop rotation combinations. In comparison with cotton monoculture sown either after conventional tillage or on permanent beds, soil water storage, particularly during the early part of growing season when rainfall provided the major proportion of crop water requirements, and drainage were greatest when a cotton-wheat rotation was sown on permanent beds. Seasonal drainage out of the 1.2 m depth, averaged among all seasons, was of the order of 25 mm, 33 mm and 70 mm with cotton monoculture sown either after conventional tillage or on permanent beds, and a cotton-wheat rotation on permanent beds, respectively. Soil water storage and drainage were also greater when irrigation frequency was greater. Seasonal drainage out of the 1.2 m depth, averaged between the 2006-07 and 2008-09 seasons, was 54 mm with “frequent irrigation”, and 28 mm with “infrequent” irrigation. Infiltration was less in management systems which resulted in wetter soil; viz. frequent irrigation or a cotton-wheat rotation on permanent beds with in situ stubble retention. Drainage water losses in a furrow-irrigated Vertisol may be reduced and soil water storage increased (i.e. water conservation improved) by sowing a cotton-wheat rotation with in situ stubble retention under less frequent irrigation.  相似文献   

17.
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18.
The objective of this study was to compare soil water measurements made using capacitance and neutron probes by means of a water balance experiment in a drainage lysimeter. The experiment was conducted in a 5-year-old drip-irrigated peach orchard (Prunus persica L. Batsch, cv. Flordastar, on GF-677 peach rootstock) planted in a clay loam textured soil located in southern Spain. Four drainage lysimeters (5 m × 5 m × 1.5 m), each containing one tree, were constructed and equipped with one lateral line containing eight drippers per tree, with a discharge rate of 2 L h−1. Three access tubes for the neutron probe (NP), symmetrically facing three PVC access tubes containing the multi-depth capacitance probes (MDCP) were located perpendicularly to the drip line (0.2, 0.6 and 1 m). The results demonstrated that both the capacitance and neutron probes gave similar soil water content values under steady state hydraulic gradient conditions (0.2 m from the emitter) although some discrepancies were found in heterogeneous soil water distribution conditions (1 m from the emitter), which might be attributed to the smaller soil volume explored by the MDCP compared with the NP. Explanations for the discrepancies between both devised are presented. When water inputs and outputs were fairly constant, the volumetric soil water content could be considered to represent field saturation (θsat = 0.36 m3 m−3). When drainage was zero, there were 2 days when the soil water content was constant and could be considered as field capacity (θfc = 0.31 m3 m−3). The findings suggest that: (i) capacitance probes can be used for continuous real-time soil water content monitoring unlike the manual measurements obtained with the neutron probe; (ii) the location of the sensors is critical when used for drip irrigation scheduling and our recommendations for practical agricultural purposes would be to place MDCP sensors in the place representing the highest root density, leading the sensors to become biological sensors rather than mere soil moisture sensors; and (iii) on average, the water balance values determined by lysimeter match those calculated using the data from both probes. However, due to the smaller soil volume explored by MDCP, more of these sensors must be used to characterize the soil water status in water balance studies.  相似文献   

19.
This study evaluated the performance of three soil water content sensors (CS616/625, Campbell Scientific, Inc., Logan, UT; TDT, Acclima, Inc., Meridian, ID; 5TE, Decagon Devices, Inc., Pullman, WA) and a soil water potential sensor (Watermark 200SS, Irrometer Company, Inc., Riverside, CA) in laboratory and field conditions. Soil water content/potential values measured by the sensors were compared with corresponding volumetric water content (θv, m3 m−3) values derived from gravimetric samples, ranging approximately from the permanent wilting point (PWP) to field capacity (FC) volumetric water contents. Under laboratory and field conditions, the factory-based calibrations of θv did not consistently achieve the required accuracy for any sensor in the sandy clay loam, loamy sand, and clay loam soils of eastern Colorado. Salt (calcium chloride dihydrate) added to the soils in the laboratory caused the CS616, TDT, and 5TE sensors to experience errors in their volumetric water content readings with increased bulk soil electrical conductivity (EC; dS m−1). Results from field tests in sandy clay loam and loamy sand soils indicated that a linear calibration (equations provided) for the TDT, CS616 and 5TE sensors (and a logarithmic calibration for the Watermark sensors) could reduce the errors of the factory calibration of θv to less than 0.02 ± 0.035 m3 m−3. Furthermore, the performance evaluation tests confirmed that each individual sensor needed a unique calibration equation for every soil type and location in the field. In addition, the calibrated van Genuchten (1980) equation was as accurate as the calibrated logarithmic equation and can be used to convert soil water potential (kPa) to volumetric soil water content (m3 m−3). Finally, analysis of the θv field data indicated that the CS616, 5TE and Watermark sensor readings were influenced by diurnal fluctuations in soil temperature, while the TDT was not influenced. Therefore, it is recommended that the soil temperature be considered in the calibration process of the CS616, 5TE, and Watermark sensors. Further research will be aimed towards determining the need of sensor calibration for every agricultural season.  相似文献   

20.
Results from a field experiment examining soil water fate within U.S. Golf Association (USGA) putting greens were used to examine the validity of a water flow simulation model. The experiment used six different sandy root zones each with depths of 300 mm overlying a 100 mm thick gravel layer. Data collected over two growing seasons consisted of measured rainfall, irrigation, drainage volume, and soil water contents; and calculated turfgrass evapotranspiration (ET). Turfgrass rooting was measured at the end of each growing season, and water retention curve and saturated hydraulic conductivity measurements were conducted at the end of the study. For each root zone treatment, HYDRUS-2D (H2D) was calibrated using a subset of the experimental data and then validated by comparing observed and predicted water contents at 76, 152 and 229 mm depth and over both growing seasons. Model efficiency (E) ranged from 0.33 to 0.78; Mean Absolute Error (MAE) ranged from 0.012 to 0.024 m3 m−3; and Root Mean Square Error (RMSE) ranged from 0.015 to 0.028 m3 m−3, for the six treatments and both years. Also, RMSE values were at best slightly larger than and at worst twice as large as the mean standard deviation values of replicate measurements. Thus, H2D simulation performed reasonably well in describing the water content results of the field study. The calibration results provide evidence of hysteresis in water retention where water retention properties from the field appear to follow the sorption or wetting curve as compared with the laboratory measurements following the desorption or drying curve. This suggests that standard laboratory measurements of water release would not precisely predict water retention behavior in the field and over estimate water storage of these capillary barrier soils. The validation results provide evidence for turfgrass use of perched water held within these profiles, even though turfgrass rooting is shallow and water storage principally occurs deep within the root zone. Thus, the perched water of USGA putting greens should serve reasonably well as a water reservoir for subsequent turfgrass use, allowing for water conserving irrigation practices that makes use of this stored water.  相似文献   

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