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1.
Implementation of improved irrigation schedules in some semiarid zones improve water efficiency and can be recommended where occasional periods of heavy rainfall may remove some of the accumulated salts. We hypothesized, however, that the leaching pattern of the main ions may differ regarding their potential contribution to the total salt discharge. The experiment was conducted near Madrid in Spain on a typical Xerofluvent soil with sandy-loam texture in the first 0.5 m. For 4 years, a traditional crop rotation of corn–wheat–corn–oat (Zea mays L.–Triticum aestivum L.–Zea mays L.–Avena sativa L.) was planted and two irrigation treatments (traditional and improved) were applied only to the corn. In an experimental set-up of 24 plots, samples of the soil solutions were extracted 61 times during the experiment at soil depths of 0.4, 0.9 and 1.4 m. During the experiment, drainage volume was estimated in plots under the two irrigation schedules. Main ions in the soil solution were SO42−, Cl, Ca2+, Na+ and HCO3. These solutes accounted for 88% of total salt discharge under the two irrigation treatments. Two main patterns of salt leaching were observed. For most main ions, except HCO3, the input to discharge ratio was lower than one. Also for HCO3, the irrigation treatment did not affect the leaching pattern (higher input than discharge under the two irrigation treatments). Improved irrigation schedules can be implemented without increasing the total salt load, but attention should be paid to specific leaching patterns of individual ions.  相似文献   

2.
半湿润区苹果树冠层降雨截留模型应用研究   总被引:2,自引:0,他引:2  
基于苹果树冠层截留的观测数据,研究了苹果树的冠层截留特征。结果表明,①果树冠层截留量、穿透雨量、树干茎流量均与降雨量有着明显的相关性。冠层截留量与降雨量之间呈对数关系;穿透流量、树干茎流量与降雨量之间分别呈线性关系。林外降雨大于1mm时产生穿透雨,大于1.5mm时产生树干茎流。果树冠层平均截留率为18%,冠层饱和截留量为7.5mm。②通过29场降雨试验,获得了适合京郊苹果树的冠层截留模型,并对该模型与常见冠层截留模型的模拟结果进行了对比分析。  相似文献   

3.
Heavy rainfall and irrigations during the summer months in the North China Plain may cause losses of nitrogen because of nitrate leaching. The objectives of this study were to characterize the leaching of accumulated N in soil profiles, and to determine the usefulness of Br as a tracer of surface-applied N fertilizer under heavy rainfall and high irrigation rates. A field experiment with bare plots was conducted near Beijing from 5 July to 6 September 2006. The experiment included three treatments: no irrigation (rainfall only, I0), farmers’ practice irrigation (rainfall plus 100 mm irrigation, I100) and high-intensity irrigation (rainfall plus 500 mm irrigation, I500), with three replicates. Transport of surface-applied Br and NO3 (assuming no initial NO3 in the soil profile) and accumulated NO3 in soil profiles were all simulated with the HYDRUS-1D model. The model simulation results showed that Br leached through the soil profile faster than NO3. When Br was used as a tracer for surface-applied N fertilizer to estimate nitrate leaching losses, the amount of N leaching may be overestimated by about 10%. Water drainage and nitrate leaching were dramatically increased as the irrigation rate was increased. The amounts of N leaching out of the 2.1-m soil profile under I0, I100 and I500 treatments were 195 ± 84, 392 ± 136 and 612 ± 211 kg N ha−1, equivalent to about 20 ± 5%, 40 ± 6% and 62 ± 7% of the accumulative N in the soil profile, respectively. N was leached more deeply as the irrigation rate increased. The larger amount of initial accumulated N was in soil profile, the higher percentage of N leaching was. N leaching was also simulated in summer under different weather conditions from 1986 to 2006. The results indicated that nitrate leaching in rainy years were significantly higher than those in dry and normal years. Increasing the irrigation times and decreasing the single irrigation rate after fertilizer application should be recommended.  相似文献   

4.
Drought and fresh water shortage are in the way of sustainable agriculture development in the North China Plain. The scarcity of fresh water forces farmers to use shallow saline ground water, which helps to overcome drought and increase crop yields but also increases the risk of soil salinization. This paper describes salt regimes and crop responses to saline irrigation water based on field experiments conducted from October 1997 to September 2005. It was found that use of saline water causes the ECe of the topsoil (0–100 cm, Cv: 0.196∼0.330) to be higher and more variable than the subsoil (100–180 cm, Cv: 0.133∼0.219). The salt load rapidly increased, notably in the upper 80 cm and especially during the season of October 1999 to June 2000. It was concluded that the maximum soil depth to which the soil was leached during the wet season was about 150 cm. The relative yields of winter wheat could be ranked Fresh Sufficient (FS, 100%) > Fresh Limited (FL, 91.80%) > Saline Sufficient (SS, 91.63%) > Saline Limited (SL, 88.28%) > Control (C, 69.58%) and for maize FS (100%) > FL (96.37%) > SS (93.05%) > SL (90.04%)> C (89.81%). The best irrigation regime was Saline Limited for winter wheat and maize, provided rainfall is sufficient. The experiments confirm that saline irrigation water appears to be economically attractive to farmers in the short term and ecological hazards can still be controlled with proper leaching.  相似文献   

5.
A five-year experiment (2002–2006) was conducted to determine apple (cv ‘Golden Smoothee’) and pear (cv ‘Conference’) crop coefficients (Kc) using two large weighing lysimeters. Daily reference evapotranspiration (ETo) and crop evapotranspiration (ETc) were evaluated. Midday canopy light interception of both crops planted in hedgerows, 4 × 1.6 m, was determined on a weekly basis from bud-break until leaf fall from year 2002 (fourth after planting) to year 2006 of both plantations. Relationships between canopy light interception and calculated Kc (ETc/ETo) were evaluated from bud-break until harvest. There were differences in Kc values between apple and pear trees. When daily Kc values from bud-break until harvest were adjusted to hyperbolic functions each year, adjusted curves for pear trees were very similar regardless of year (maximum Kc around 1.0). In apple trees, the maximum values of Kc increased over time, from 0.49 in 2002 to 1.04 in 2006. Midday light interception in both apple and pear trees increased during the 5 years of experiment from 29.0 to 45.6% in apples and from 27.5 to 41.6% in pears in midsummer. Although there was a significant positive correlation between midday canopy light interception and Kc in apple and pear trees, in different times within a specific year, these relationships were different between crops. While the apple data fitted into the same equation regardless of the year, different equations were needed to fit the pear data in different years. This discrepancy may have been related to differences in the canopy properties between apple and pear trees. Pear canopies had higher porosity than apple canopies and thus improved light penetration. Apple trees were more vigorous and produced taller and denser canopies. Pear Kc values were greatly influenced by the evaporative demands of different years and consequently differences in midday canopy light interception did not adequately reflect the differences in Kc across the two species.  相似文献   

6.
Coal bed natural gas (CBNG) extraction in the Powder River (PR) Basin of Wyoming and Montana produces modestly saline-sodic wastewater, which may have electrical conductivity (EC) and sodium adsorption ratios (SAR) exceeding accepted thresholds for irrigation (EC = 3 dS m−1, SAR = 12 (mmolc l−1)1/2. As an approach to managing large volumes of CBNG-produced water, treatment processes have been developed to adjust produced water salinity and sodicity to published irrigation guidelines and legislated in-stream standards. The objective of this laboratory study was to assess acute and chronic soil solution EC and SAR responses to various wetting regimes simulating repeated flood irrigation with treated CBNG product water, followed by single rainfall events. Fifty-four soil samples from irrigated fields in southeast Montana were subjected to simulated PR water or CBNG water treated to EC and SAR values accepted as thresholds for designation of saline × sodic water, in a single wetting event, five wetting–drying events, or five wetting–drying events, followed by leaching with distilled water. Resultant saturated paste extract EC (ECe) and SAR of soils having <33% clay did not differ from one another, but resulting ECe and SAR were all less than those for soil having >33% clay. Repeated wetting with PR water having EC of 1.56 dS m−1 and SAR of 4.54 led to SAR <12, but brought ECe near 3 dS m−1. Repeated wetting with water having salinity = 3.12 dS m−1 and SAR = 13.09 led to ECe >3 dS m−1 and SAR near 12. Subsequent inundation and drainage with distilled water, simulating rainfall-quality leaching, reduced ECe and SAR more often in coarse-textured, high salt content soils than in finer-textured, lower salt content soils. Decreases in ECe upon leaching with distilled water were of greater magnitude than corresponding decreases in SAR, reinforcing supposition of sodium-induced dispersion of fine-textured soils as a consequence of rainfall following irrigation with water having salinity and sodicity levels equal to previously published thresholds.  相似文献   

7.
Laboratory experiments were conducted to investigate the distributions of water and nitrate from a buried dripline discharging an ammonium nitrate solution in uniform and layered-textural soils. Two layered soils, a sandy-over-loam soil (SL) and a loam-sandy-loam soil (LSL), and two uniform soils of sandy (S) and loam (L) were tested. The experimental results demonstrated that dripline depth and layered-textural soil greatly affected water and nitrate distribution. Wetted depth increased with dripline depth and initial soil water content for both uniform and layered soils. The distribution pattern of water in the layered soils was controlled by the layering sequence and the dripline position relative to the interface between two soil layers. Water accumulation occurred in the fine-textural layer of soil for the layered soils. For the sandy-over-loam soil (SL), positioning the dripline below the interface led to much water (89%) moving to the sublayer of loam soil than positioning the dripline above the interface (73%). For the loam-sandy-loam soil (LSL), positioning the dripline in the top layer of loam soil resulted in 77% of water applied distributed in the top layer, while positioning the dripline in the bottom layer of loam soil resulted in 93% of water applied distributed in the bottom layer. Measurements of nitrate distribution showed that nitrate concentration in the proximity of the dripline and of the water accumulation zone approximated the input concentration while nitrate accumulated at the boundary of the wetted volume for both uniform and layered soils tested. The results from this study suggest that the dripline depth should be carefully selected in the design of subsurface drip irrigation systems for layered soils to obtain a target distribution of water and nitrate.  相似文献   

8.
A model was developed to predict rootzone salinity under different irrigation practices on different soil types, with similar rainfall but different monthly distributions. A rootzone daily water and salt balance was performed using eight scenarios: two soil types (coarse textured vs. fine textured), two multi-year series of actual rainfall data and two irrigation practices (surface with fixed number of irrigations and ET-based sprinkler irrigation). All factors influenced the mean electrical conductivity (EC) of the rootzone in the growing season (ECeS): (i) Surface irrigation led to lower ECeS than sprinkler irrigation; (ii) Winter-concentrated rainfall caused lower ECeS than rainfall distributed uniformly throughout the year; and (iii) Coarser-textured soil usually resulted in lower ECeS than the finer textured. The ECeS was related to the total precipitation of the hydrologic year and to the annual leaching fraction (LF) but surprisingly not to the seasonal LF. In most cases, the model predicted lower ECeS than the FAO steady-state approach. Therefore, considering these site-specific features could lead to lower leaching requirements and the safe use of higher salinity water.  相似文献   

9.
Spatial and temporal variability of nitrate in irrigated salad crops   总被引:2,自引:0,他引:2  
The objective of this study was to analyze the spatial and seasonal variations in NO3 -N concentration in soil samples and solution samplers and the N leaching of an irrigated crop cultivated intensively in the Mediterranean zone. Although much information is available from controlled field experiments concerning N concentration and its spatial variability, quantitative estimates of nitrate fluxes under normal farming conditions and when the field is directly managed by farmers are rare. This is particularly true for gardening crops in the Mediterranean zone, where high evapotranspiration rates lead to intensive irrigation and may be responsible for N leaching. A field experiment was conducted in the Departement du Gard under agricultural conditions. Salads (Cichorium endivia, Lactuca sativa) were planted in three consecutive periods. The field was irrigated with sprinklers. Local measurements with a neutron probe were made at two sites (row, interrow), and an experimental plot (95 m×25 m) was surveyed at 36 points located on a 10 m×10 m equilateral grid to analyze the spatial variability of water and NO3 -N balances. To analyze the basic statistical properties of our sampling scheme, random fields of soil concentration were simulated with the turning-bands method. Sampling strategy simulations indicated that when a spatial structure exists, sampling according to a regular grid was more efficient than a purely random sampling strategy. Global trends indicated high spatial variability for nitrate leaching with differences between periods of different irrigation intensity (97 kg ha–1 NO3 -N leaching during the spring and summer, and 199 kg ha–1 NO3 -N leaching during autumn and winter). Leaching caused temporal variations in the spatial distributions of NO3 -N. The origin of the spatial variability of N leaching was explained by first, the variability in NO3 -N concentration in the soil profile, and second, by spatial variability in irrigation. Furthermore, the spatial distribution of the NO3 -N concentration was time dependent, and NO3 -N spatial distributions became independent after approximately 2 or 3 months under our conditions. Our results show that better management of irrigation and fertilizer in spring and summer may reduce N leaching and, thus, improve ground water quality. Received: 15 March 1996  相似文献   

10.
Agricultural systems with grazing animals are increasingly under scrutiny for their contribution to quality degradation of waterways and water bodies. Soil type, climate, animal type and nitrogen (N) fertilisation are contributors to the variation in N that is leached through the soil profile into ground and surface water. It is difficult to explore the effect of these factors using experimentation only and modelling is proposed as an alternative. An agro-ecosystem model, EcoMod, was used to quantify the pastoral ecosystem responses to situational variability in climate and soil, choice of animal type and N fertilisation level within the Lake Taupo region of New Zealand. Factorial combinations of soil type (Oruanui and Waipahihi), climate (low, moderate and high rainfall), animal type (sheep, beef and dairy) and N fertilisation level (0 or 60 kg N/ha/yr) were simulated. High rainfall climates also had colder temperatures, grew less pasture and carried fewer animals overall which lead to less dung and urinary N returned. Therefore, even though a higher proportion of N returned ultimately leached at the higher rainfall sites, the total N leached did not differ greatly between sites. Weather variation between years had a marked influence on N leaching within a site, due to the timing and magnitude of rainfall events. In this region, for these two highly permeable soil types, N applied as fertiliser had a high propensity to leach, either after being taken up by plants, grazed and returned to the soil as dung and urine, or due to direct flow through the soil profile. Soil type had a considerable effect on N leaching risk, the timing of N leaching and mean pasture production. Nitrogen leaching was greatest from beef cattle, followed by dairy and sheep with the level of leaching related to urine deposition patterns for each animal type and due to the amount of N returned to the soil as excreta. Simulation results indicate that sheep farming systems with limited fertiliser N inputs will reduce N leaching from farms in the Lake Taupo catchment.  相似文献   

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