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1.
Farm management models often produce average crop shares over a number of years, whereas models from the natural sciences often require inputs of sequences of crops grown on a specific field over several years. In interdisciplinary modelling, this difference can be a relevant obstacle. To bridge this gap, an approach is presented that allows disaggregating results from farm management models to the level required by many natural science models. The approach presented includes two methodological innovations: first, minimum cross entropy is used to ensure a unique solution when modelling a linear programming model at the field level, even when objective and constraint coefficients are identical for different fields. Second, the use of a calibrated Markov chain approach allows the creation of land-use sequences that are closer to the linear programming model’s results than an unconditional stochastic simulation would be. The calibrated Markov chain makes use of a prior matrix of transition probabilities that can be empirically derived. Both simulations and analytical calculations with case study data show that the variances of the Markov chain approach are systematically lower than those yielded by a simple stochastic simulation approach. The approach introduced in this paper can improve the coupling of farm-level economic models with natural science models at the field level.  相似文献   

2.
Ethiopia’s economy is dependent on agriculture which contributes more than 50% to GDP, about 60% to foreign exchange earning and provides livelihood to more than 85% of the population. Ethiopia has a large potential of water resources that could be developed for irrigation. Despite the large water resources, Ethiopia continues to receive food aid to about 10% of the population who are at risk annually, out of a total of more than 67 million. The government of Ethiopia is committed to solving this paradox through an agricultural led development program that includes irrigation development as one of the strategies. This paper compares rainfed and irrigated agricultural production in Ethiopia. Using the stochastic production frontier approach, the study concludes that irrigation development in Ethiopia is a viable development strategy but attention needs to be paid to improving the technology available to farmers under both rainfed and irrigated production.  相似文献   

3.
Crop water requirements for rainfed and irrigated grain corn in China   总被引:1,自引:0,他引:1  
A basic parametric crop water use model (WATER) that employes climatic and environmental data to calculate temporal and spatial water consumption for a variety of major corps was applied specifically for grain corn to the region of China and Korea to investigate the evapotranspiration (ET) demand on grain corn and the associated irrigation water applications necessary for optimal crop production. A network of 241 stations provided the seasonal climatic input. The climatic input consisted of data averaged over approximately a 20 year period. Among the results, highest ET under full irrigation (first harvest) occurred in the northwestern inland sections of China, whereas least ET was found for the southeast. Under rainfed conditions, the relationship became nearly inverse. In order to achieve optimum crop yields, about 1000 mm of irrigation water was needed in the northwest, contrasted with none required in the south and east of China. A sensitivity analysis was applied to determine the degree of error introduced by faulty or uncertain environmental input data.  相似文献   

4.
Crop water requirements for rainfed and irrigated wheat in China and Korea   总被引:2,自引:0,他引:2  
The parametric crop water use model (WATER) was applied for winter wheat to China and its environs in order to examine the evapotranspiration requirements under rainfed conditions and the associated irrigation water applications necessary for optimal production. A network of 241 stations provided climatic data averaged over a 20 year period. Highest ET under full irrigation (first growing season) was observed in the northwestern inland sections of China and the eastern portions of the Tibetan Plateau, while lowest ET occurred in the southeast; under rainfed conditions, these tendencies nearly reversed. About 400 mm of irrigation water was required in the northwest in order to achieve near-optimum yields in contrast with no such water requirements in the central east of China. A sensitivity analysis was conducted to determine the errors introduced by faulty, uncertain, or missing station data.  相似文献   

5.
The growing pressure on fresh water resources demands that agriculture becomes more productive with its current water use. Increasing water productivity is an often cited solution, though the current levels of water productivity are not systematically mapped. A global map of water productivity helps to identify where water resources are productively used, and identifies places where improvements are possible. The WATPRO water productivity model for wheat, using remote sensing data products as input, was applied at a global scale with global data sets of the NDVI and surface albedo to benchmark water productivity of wheat for the beginning of this millennium. Time profiles of the NDVI were used to determine the time frame from crop establishment to harvest on a pixel basis, which was considered the modelling period. It was found that water productivity varies from approximately 0.2 to 1.8 kg of harvestable wheat per cubic metre of water consumed. From the 10 largest producers of wheat, France and Germany score the highest country average water productivity of 1.42 and 1.35 kg m−3, respectively. The results were compared with modelling information by Liu et al. (2007) who applied the GEPIC model at a global scale to map water productivity, and by Chapagain and Hoekstra (2004) who used FAO statistics to determine water productivity per country. A comparison with Liu et al. showed a good correlation for most countries, but the correlation with the results by Chapagain and Hoekstra was less obvious. The global patterns of the water productivity map were compared with global data sets of precipitation and reference evapotranspiration to determine the impact of climate and of water availability reflected by precipitation. It appears that the highest levels of water productivity are to be expected in temperate climates with high precipitation. Due to its non-linear relationship with precipitation, it is expected that large gains in water productivity can be made with in situ rain water harvesting or supplemental irrigation in dry areas with low seasonal precipitation. A full understanding of the spatial patterns by country or river basin will support decisions on where to invest and what measures to take to make agriculture more water productive.  相似文献   

6.
Crop growth models have been used in simulating the soil water balance for purposes of irrigation management and yield predictions. The application of CropSyst, a cropping systems simulation model, was evaluated for Cedara, South Africa. Simulations included soil water balance of fallow land and rainfed and irrigated winter crops [oats (Avena sativa), Italian ryegrass (Lolium multiflorum) and rye (Secale cereale)]; and irrigation scheduling of the winter crops. Soil, plant, weather and management inputs were used for the soil water balance simulations. Model crop parameters were used from past experiments or obtained from model documentation, with a slight modification to account for varietal differences. The fallow land soil water simulations were more accurate for dry than for wet soil. For all three winter crops, the model consistently over-estimated the soil water content in the upper layers, with a good agreement for the deeper layers until a large precipitation event occurred to which the model responded more slowly than that observed. Simulations using model-scheduled irrigation based on 0.4 and 0.6 maximum allowable depletion criteria indicated that the observed applied irrigation in the field was more than that required. Soil water depletion and accumulated transpiration simulations were similar in both the observed and model-scheduled irrigations, but total soil evaporation and percolation were greater in the case of the observed than the model-scheduled irrigations. Irrigation scheduling using crop growth models may assist in avoiding over- or under-application of irrigation applications by ensuring efficient utilization of rain and irrigation.  相似文献   

7.
Consumptive water use and crop coefficients of irrigated sunflower   总被引:1,自引:1,他引:1  
In semi-arid environments, the use of irrigation is necessary for sunflower production to reach its maximum potential. The aim of this study was to quantify the consumptive water use and crop coefficients of irrigated sunflower (Helianthus annuus L.) without soil water limitations during two growing seasons. The experimental work was conducted in the lysimeter facilities located in Albacete (Central Spain). A weighing lysimeter with an overall resolution of 250 g was used to measure the daily sunflower evapotranspiration throughout the growing season under sprinkler irrigation. The lysimeter container was 2.3 m × 2.7 m × 1.7 m deep, with an approximate total weight of 14.5 Mg. Daily ET c values were calculated as the difference between lysimeter mass losses and lysimeter mass gains divided by the lysimeter area. In the lysimeter, sprinkler irrigation was applied to replace cumulative ET c, thus maintaining non-limiting soil water conditions. Seasonal lysimeter ET c was 619 mm in 2009 and 576 mm in 2011. The higher ET c value in 2009 was due to earlier planting and a longer growing season with the maximum cover coinciding with the maximum ET o period. For the two study years, maximum average K c values reached values of approximately 1.10 and 1.20, respectively, during mid-season stage and coincided with maximum ground cover values of 75 and 88 %, respectively. The dual crop coefficient approach was used to separate crop transpiration (K cb) from soil evaporation (K e). As the crop canopy expanded, K cb values increased while the K e values decreased. The seasonal evaporation component was estimated to be about 25 % of ET c. Linear relationships were found between the lysimeter K cb and the canopy ground cover (f c) for the each season, and a single relationship that related K cb to growing degree-days was established allowing extrapolation of our results to other environments.  相似文献   

8.
Scarcity of water is a critical limitation to adoption of modern technology for increasing productivity of traditional rainfed rice growing areas of eastern Madhya Pradesh, India. The shortage of water results from uneven distribution of rains, significant gaps between rain events and field water losses rather than from low seasonal or annual rainfall totals. A feasible strategy to alleviate this limitation is to harvest excess rainwater in a farm pond during the wet season and use the conserved water for crop production in both wet (as insurance against drought) and dry seasons by adopting suitable crop and cropping systems. The results of water balance in a 1.05 ha field, on which a farm pond was built using 0.09 ha area, showed that 28–37% of seasonal rainfall was available as surface runoff from microcatchment (0.66 ha growing soybean, peanut and pigeonpea) for collection in the pond. This was sufficient for saving rice in a 0.30 ha area (in the lower side of the field) from drought stress, and for establishment of chickpea and mustard (in 0.90 ha) in the post-rainy season after harvest of rainy season crops. Soybean, peanut and pigeonpea, grown in the microcatchment during the rainy season, utilized respectively 371–726, 364–733 and 535–920 mm water in evapotranspiration (E,) and deep percolation (P). Rice grown below the pond required 28–317 mm water in different seasons to save the crop from in-season drought stress which commonly occurred during vegetative and reproductive stages. Water requirement (E, + P) of rice was 816–1342 mm in different seasons. Residual soil moisture after rainy season soybean, peanut and rice was sufficient (172–203 mm) to support post rainy season crops of chickpea and mustard. However, the losses of moisture from the soil surface layer after harvest of rainy season crops were rapid (7–23 mm), which necessitated a light irrigation (21–45 mm) for establishment of chickpea and mustard in the post-rainy season. The water balance results of soybean-mustard, peanut-mustard and peanut-chickpea were near identical to soybean-chickpea cropping. Similarly the water balance of rice-mustard was identical to Corresponding author. rice-chickpea in the vertisols. Soybean-mustard and rice-chickpea were the suitable and economical cropping systems for the microcatchment and service area of the farm pond.  相似文献   

9.
《Agricultural Systems》2003,76(1):273-292
This paper proposes an Opportunity Index (Oi) for site-specific crop management (SSCM). In contrast to the traditional practice of uniform agronomic management, SSCM aims to match controllable inputs with spatially variable crop requirements. Farmers, however, are often left wondering how their yield maps can be used to justify a change to SSCM. The Oi is a single number that may be used in the process of this justification. The Oi is based on three components: (1) the magnitude of variation present in a yield map, relative to a certain threshold; (2) the average area within which yield is autocorrelated, relative to the minimum area within which variable-rate controllers (which physically implement SSCM) can reliably operate; and, (3) the economic and environmental benefit of SSCM relative to uniform management. The Oi was calculated for 20 Australian cropping fields and compared with b′ [Journal of Agricultural Sciences, Cambridge, 28 (1938)], which is an alternative method of quantifying the management opportunity from yield variation. A weak negative correlation was found to exist. Results suggest that a good opportunity for site-specific crop management exists when the Oi is greater than 20, although this is only a tentative recommendation.  相似文献   

10.
New cultivars of sorghum for biomass energy production are currently available. This crop has a positive energy balance being irrigation water the largest energy consumer during the growing cycle. Thence, it is important to know the biomass sorghum water requirements, in order to minimize irrigation losses, thus saving water and energy. The objective of this study was to quantify the water use and crop coefficients of irrigated biomass sorghum without soil water limitations during two growing seasons. A weighing lysimeter located in Albacete (Central Spain) was used to measure the daily biomass sorghum evapotranspiration (ETc) throughout the growing season under sprinkler irrigation. Seasonal lysimeter ETc was 721 mm in 2007 and 691 mm in 2010. The 4 % higher ETc value in 2007 was due to an 8 % higher evaporative demand in that year. Maximum average K c values of 1.17 in 2007 and 1.21 in 2010 were reached during the mid-season stage. The average K c values for the 2 years of study were K c-ini: 0.64 and K c-mid: 1.19. The seasonal evaporation component was estimated to be about 18 % of ETc. The average basal K c (K cb) values for the two study years were K cb-ini: 0.11 and K cb-mid: 1.17. The good linear relationship found between K cb values and the fraction of ground cover (f c) and the excellent agreement found between Normalized Difference Vegetation Index and different biophysical parameters, such as K cb and f c, will allow monitoring and estimating the spatially distributed water requirements of biomass sorghum at field and regional scales.  相似文献   

11.
Evaluation of crop water stress index for LEPA irrigated corn   总被引:6,自引:0,他引:6  
This study was designed to evaluate the crop water stress index (CWSI) for low-energy precision application (LEPA) irrigated corn (Zea mays L.) grown on slowly-permeable Pullman clay loam soil (fine, mixed, Torrertic Paleustoll) during the 1992 growing season at Bushland, Tex. The effects of six different irrigation levels (100%, 80%, 60%, 40%, 20%, and 0% replenishment of soil water depleted from the 1.5-m soil profile depth) on corn yields and the resulting CWSI were investigated. Irrigations were applied in 25 mm increments to maintain the soil water in the 100% treatment within 60–80% of the “plant extractable soil water” using LEPA technology, which wets alternate furrows only. The 1992 growing season was slightly wetter than normal. Thus, irrigation water use was less than normal, but the corn dry matter and grain yield were still significantly increased by irrigation. The yield, water use, and water use efficiency of fully irrigated corn were 1.246 kg/m2, 786 mm, and 1.34 kg/m3, respectively. CWSI was calculated from measurements of infrared canopy temperatures, ambient air temperatures, and vapor pressure deficit values for the six irrigation levels. A “non-water-stressed baseline” equation for corn was developed using the diurnal infrared canopy temperature measurements as T cT a = 1.06–2.56 VPD, where T c was the canopy temperature (°C), Ta was the air temperature (°C) and VPD was the vapor pressure deficit (kPa). Trends in CWSI values were consistent with the soil water contents induced by the deficit irrigations. Both the dry matter and grain yields decreased with increased soil water deficit. Minimal yield reductions were observed at a threshold CWSI value of 0.33 or less for corn. The CWSI was useful for evaluating crop water stress in corn and should be a valuable tool to assist irrigation decision making together with soil water measurements and/or evapotranspiration models. Received: 19 May 1998  相似文献   

12.
This work assesses the seasonal dynamics of the substrate oxygen content and the response to nutrient solution oxygen enrichment (oxyfertigation) of an autumn-spring tomato crop grown on rockwool slabs and irrigated with treated wastewater of very low dissolved oxygen (DO) content under Mediterranean greenhouse conditions. DO values in the nutrient solution were clearly higher for the oxygen-enriched (14.6 mg L−1) tomato crop than for the non-enriched one (4.5 mg L−1). However, DO values in the substrate solution were similar for both oxygen treatments (mean seasonal values of 5.1 and 4.8 mg L−1 for the enriched and the non-enriched one, respectively), except for a short crop period at the end of the cycle when they were significantly higher for the oxygen-enriched crop. For both treatments, substrate DO values were highest for the winter period and decreased progressively during the spring period, reaching minimum values of around or below 3 mg L−1 at the end of the spring. The oxygen enrichment of the nutrient solution did not affect any of the irrigation and fertigation parameters evaluated in the tomato crop: water uptake, volumetric water content of the substrate, electrical conductivity (EC) or nutrient concentration in the leached nutrient solution. Moreover, the oxygen enrichment of the nutrient solution did not affect the aboveground biomass and the biomass partitioning, the fresh weight of total and marketable tomato fruits or the tomato fruit quality parameters. Overall, it appears that oxygen deficiency conditions did not occur as the substrate DO values were higher than, or about, 3 mg L−1 throughout most of the tomato crop cycle for both treatments and the rockwool slabs maintained good aeration conditions throughout the whole cycle.  相似文献   

13.
Soil-water conditions for ricefields located in valleys in micro-catchments are simulated using a daily soil-water balance model. The crop is primarily rainfed but there is also limited irrigation water. The simulation covers a complete year and includes features such as rainfall, irrigation releases, runoff from uplands, actual evaporation and evapotranspiration, percolation losses through the bed and bunds of the ricefield, standing water in the field and overflows from the ricefield. A specific location in Sri Lanka is selected to illustrate the approach. The impacts of different conditions are explored including alternative irrigation releases, increased losses through the bed and bunds of the ricefield and a lower overflow from the ricefield. Simulations indicate that ricefields which are towards the valley sides have an increased inflow due to runoff from adjacent uplands; this can lead to improved rice yields. However, reducing heights of the bunds to half the original value results in substantial overflows during periods of high rainfall while the number of days without submergence almost doubles. This uncomplicated model is consistent with the limited field data and information available; it provides a realistic representation of the important processes and indicates why poor crop yields often occur.  相似文献   

14.
15.
Crop water use efficiency of irrigated cotton was hypothesized to be improved by a combination of minimum tillage and sowing a wheat (Triticum aestivum L.) rotation crop. This hypothesis was evaluated in a Vertisol near Narrabri, Australia from 1997 to 2003. The experimental treatments were: continuous cotton sown after conventional or minimum tillage and minimum-tilled cotton–wheat. Soil water content was measured with a neutron moisture meter, and runoff with trapezoidal flumes. Application efficiency of irrigation water was estimated as the amount of infiltrated water/total amount applied. Plant available water was estimated using the maximum and minimum soil water storage during the growing season. Evapotranspiration was estimated with the water balance method using measured and simulated soil water data. Seasonal evapotranspiration was partitioned into that coming from rainfall, irrigation and stored soil water. Crop water use efficiency was calculated as cotton lint yield per hectare/seasonal evapotranspiration. Rotation of cotton with wheat and minimum tillage improved water use efficiency in some years and application efficiency in all years. Average seasonal evapotranspiration was higher with minimum tillage than with conventional tillage. In years when cotton was sown in all plots, average cotton crop water use efficiencies were 0.23, 0.23 and 0.22 kg (lint)/m3 for minimum-tilled cotton–wheat and continuous cotton, and conventionally tilled continuous cotton, respectively. In-season rainfall efficiency, transpiration and soil evaporation were unaffected by cropping system.  相似文献   

16.
The main purpose of this paper was to evaluate whether or not the dual crop coefficient (DCC) method proposed in FAO-56 was suitable for calculating the actual daily evapotranspiration of the main crops (winter wheat and summer maize) in the North China Plain (NCP). The results were evaluated with the data measured by the large-scale weighing lysimeter at the Yucheng Comprehensive Experimental Station (YCES) of the Chinese Academy of Sciences (CAS) from 1998 to 2005 using the Nash-Sutcliffe efficiency (NSE), the root mean square error (RMSE) and the root mean square error to observations’ standard deviation ratio (RSR). The evaluation results showed that the DCC method performed effective in simulating the quantity of seasonal evapotranspiration for winter wheat but was inaccurate in calculating the peak values. The RMSE value of the winter wheat during the total growing season was less than 0.9 mm/d, the NSE and RSR values during the total growing stage were “Very Good”, but the results for summer maize were “Unsatisfactory”. The recommended basal crop coefficient values Kcbtab during the initial, mid-season and end stages for winter wheat and summer maize were modified and the variation scope of basal crop coefficient Kcb was analyzed. The Kc (compositive crop coefficient, Kc = ETc/ET0, ETc here is the observed values by lysimeter, ET0 is the reference evapotranspiration) values were estimated using observed weighing lysimeter data during the corresponding stages for winter wheat and summer maize were 0.80, 1.15, 1.25, 0.95; 0.90, 0.95, 1.25, 1.00, respectively. These can be a reference for irrigation planning.  相似文献   

17.
18.
During 3 consecutive years (1991–1993) a field experiment was conducted in an intensively irrigated agricultural soil in SW Spain. The main objective of this study was to determine the water flow and nitrate (N03) leaching, below the root zone, under an irrigated maize crop and after the growing season (bare soil and rainy period). The experiment was carried out on a furrow-irrigated maize crop at two different nitrogen (N)-fertilization rates, one the highest traditionally used by farmers in the region (about 500 kg N ha−1 per year) and the other one-third of the former (170 kg N ha−1 per year). The aim was to obtain data that could be used to propose modifications in N-fertilization to maintain crop yield and to prevent the degradation of the environment. The terms for water balance (crop evapotranspiration, drainage and soil water storage) and nitrate leaching were determined by intensive field monitoring of the soil water content, soil water potential and extraction of the soil solution by a combination of neutron probe, tensiometers and ceramic suction cups. Nitrogen uptake by the plant and N03-N produced by mineralization were also determined.The results showed that, in terms of water balance, crop evapotranspiration was similar at both N-fertilization rates used. During the irrigation period, drainage below the root zone was limited. Only in 1992 did the occurrence of rainfall during the early growing period, when the soil was wet from previous irrigation, cause considerable drainage. Nitrate leaching during the whole experimental period amounted to 150 and 43 kg ha−1 in the treatments with high and low N-fertilization, respectively. This occurred mainly during the bare soil and rainy periods, except in 1992 when considerable nitrate leaching was observed during the crop season due to the high drainage. Nitrate leaching was not so high during the bare soil period as might have been expected because of the brought during the experimental period. A reduction of N-fertilization thus strongly decreased nitrate leaching without decreasing yield.  相似文献   

19.
Farming in Serbia is traditionally rainfed. Analyses show that drought events of varying severity are frequent in this region, although there is no specific pattern. There is a distinct need for an objective assessment of the impact of drought on strategic field crops, to solve the dilemma whether irrigation is required or not. For this reason, and based on available field data, the FAO AquaCrop water driven model was selected to simulate yield and irrigation water use efficiency (IWUE) for three major field crops (maize, sunflower, and sugar beet), under two scenarios: (1) natural water supply and adequate supply of nutrients, and (2) supplementary irrigation and adequate supply of nutrients. The experiments presented here were conducted between 2000 and 2007 in northern Serbia, where chernozem soil is prevalent. Data of 2003 cropping seasons were used for local calibration, whereas the remaining years for validation. Results were such that local calibration resulted in very minor changes of AquaCrop coefficients (e.g., maize basal crop coefficient, sunflower harvest index, etc.). Simulated maize yield levels exhibited the greatest departure from measured data under irrigation conditions (−3.6 and 3.3% during an extremely dry and an extremely wet year, respectively). Simulated sunflower yield levels varied by less than 10% in 8 out of 10 comparisons. The most extreme variation was noted during the extremely wet year. The difference between simulated and measured values in the case of sugar beet was from −10.2 to 12.2%. Large differences were noted only in two or three cases, under extreme climatic conditions. Statistical indicators - root mean square error (RMSE) and index of agreement (d) - for all three crops suggested that the model can be used to highly reliably assess yield and IWUE. This conclusion was derived based on low values of RMSE and high values of d (in the case of maize and sugar beet 0.999 for both yield and IWUE, and in the case of sunflower 0.999 for yield and 0.884 for IWUE). It is noteworthy that under wet conditions, the model suggested that sunflower and sugar beet do not require irrigation, as confirmed by experimental research. These data are significant because they show that the AquaCrop model can be used in impartial decision-making and in the selection of crops to be given irrigation priority in areas where water resources are limited.  相似文献   

20.
Soil moisture availability is the main limiting factor for growing second crops in rainfed rice fallows of eastern India. Only rainfed rice is grown with traditional practices during the rainy season (June–October) with large areas (13 m ha−1) remaining fallow during the subsequent dry season (November–March) inspite of annual rainfall of the order 1000–2000 mm. In this study an attempt was made to improve productivity of rainfed rice during rainy season and to grow second crops in rice fallow during dry (winter) season with supplemental irrigation from harvested rainwater. Rice was grown as first crop with improved as well as traditional farmers’ management practices to compare the productivity between these two treatments. Study revealed that 87.1–95.6% higher yield of rice was obtained with improved management over farmers’ practices. Five crops viz., maize, groundnut, sunflower, wheat and potato were grown in rice fallow during dry (winter) season with two, three and four supplemental irrigations and improved management. Sufficient amount of excess rainwater (runoff) was available (381 mm at 75% probability level) to store and recycle for supplementary irrigation to second crops grown after rice. Study revealed that supplemental irrigation had significant effect (P < 0.001) on grain yield of dry season crops and with two irrigation mean yields of 1845, 785, 905, 1420, 8050 kg ha−1 were obtained with maize (grain), groundnut, sunflower, wheat and potato (tuber), respectively. With four irrigations 214, 89, 78, 81, 54% yield was enhanced over two irrigations in respective five crops. Water use efficiency (WUE) of 13.8, 3.35, 3.39, 5.85 and 28.7 kg ha−1 was obtained in maize, groundnut, sunflower, wheat, potato (tuber), respectively with four irrigations. The different plant growth parameters like maximum above ground biomass, leaf area index and root length were also recorded with different levels of supplemental irrigation. The study amply revealed that there was scope to improve productivity of rainfed rice during rainy season and to grow another profitable crops during winter/dry season in rice fallow with supplemental irrigation from harvested rainwater of rainy season.  相似文献   

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