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1.
In paddy field, soil saturated hydraulic conductivity (K s) plays as an important component in the calculation of irrigation requirement of the water balance equation and also for irrigation efficiency. Several laboratory and field methods can be used to determine K s. Laboratory and field determinations are usually time consuming, expensive and labour intensive. Pedo-transfer functions (PTF) serve to translate the basic information found in the soil survey into a form useful for broader applications through empirical regression of functional relationships, such as simulation modelling. Since PTFs have not been applied to paddy soils in the study area, a lot of field measurements will require high labour input to determine K s hence high cost. This study attempts to seek a simplified method for determining K s values based on common existing soil properties through PTF technique. Soil samples (n = 408 samples) were collected randomly depending on the soil series within the 2,300 ha Sawah Sempadan rice cultivation area. Both field work and laboratory work were carried out. The samples were then analysed for the following properties: dry bulk density (D b), soil particle percentage (Sand-S, Silt-Si and Clay-C), organic matter (OM) and geometric mean diameter (GMD). The measured K s values were obtained by using the falling head method. The parameters were then used as inputs for developing a K s model by regression analysis using Statistical Analysis System (SAS) package. Stepwise regression analysis was applied to determine the best fit model based on R 2 and significant level. The results of the study showed that there is a high spatial variability of the saturated hydraulic conductivity in the paddy area. The best regression model for estimating K s was based on C, D b, OM and GMD with the dependent variable (K s) in a form of natural logarithm. The model inputs introduced by stepwise regression are commonly available therefore, this model is useful to replace the conventional method.  相似文献   

2.
This study was conducted to investigate the impact of water salinity (ECw) and sodicity (SARw) on saturated (Ks) and relative (Kr) hydraulic conductivities in two clay (C) and sandy clay loam (SCL) soils. The results showed that the Ks decreased with increasing SARw, and in all of water quality treatments, the Ks of SCL soil was higher than that of the C soil. Sodicity effect (even at high SARw) on the Kr of clay soil was minimized by high salinity. Although Kr of both soils similarly responded to ECw and SARw, microstructure of clay soil was more sensitive to water quality. Effect of ECw on soil structure was greater than that of SARw. In order to assess the applicability of artificial neural networks (ANNs) in estimating Ks and Kr, two types of FFBP and CFBP ANNs and two training algorithms, namely Levenberg–Marquardt (LM) and Bayesian regulation, were employed with two strategies of uniform threshold and different threshold functions. Multiple linear regressions were also used for Ks and Kr prediction. Based on the ANN results of second strategy, best topology (4–5–4–1) was belonged to CFBP network with LM algorithm, LOGSIG–LOGSIG–TANSIG threshold functions, and values of MAE and R2 are equal to 0.1761 and 0.9945, respectively. Overall, the efficacy of ANNs is much greater than regression method for Ks prediction.  相似文献   

3.
基于HJ 1B遥感数据的冬小麦旱情监测研究   总被引：3，自引：0，他引：3  
为确定植被干旱指数(TVDI)法在苏北地区冬小麦干旱监测中的适用性,利用HJ-1B星CCD、IRS数据,建立地表温度(Ts)-归一化植被指数(NDVI)特征空间,并提取TVDI,对2012年3月26日宿迁市土壤水分信息进行遥感监测,以地面样点实测数据进行验证,评价了地表温度及植被指数信息对TVDI指数变化的敏感性.结果表明,宿迁市较干旱区域主要集中在市、县的城区附近,较湿润区域主要分布在水体周围;TVDI与土壤湿度的相关性随土层深度增加而降低,其中在10 cm、20 cm深度的相关性达到极显著水平;由于Ts直接影响土壤含水量,而NDVI为间接影响,因此TVDI对Ts的敏感性大于NDVI.基于HJ-1B数据的TVDI指数法对冬小麦干旱具有较好的监测效果.  相似文献   

4.
Peanut (Arachis hypogaea L.) is commonly grown on sandy soils in warm climates where water-deficit can impose a limitation on yield. Identification of plant traits related to increased productivity under water-deficit conditions could be used to increase yields in these water-limited environments. Two traits were examined among 17 peanut genotypes. Transpiration efficiency (TE), ratio of mass increase to water transpired, was the first trait examined. TE was measured both under well-watered conditions (greenhouse) and soil drying (outdoors in pots) conditions. Virtually no difference was observed in TE among genotypes under well-watered conditions indicating the gas exchange properties were similar. However, under soil drying conditions there were substantial differences among genotypes. These results indicated that TE with drying soil might interact with traits associated with water loss on drying soils. Therefore, the second trait examined in this study was the fraction transpirable soil water (FTSW) content at which the decline in transpiration with soil drying was observed. This greenhouse experiment showed large variability among the 17 genotypes. A second-order polynomial described the relationship between TE under soil drying conditions and the threshold for the decline in transpiration. The FTSW for maximum TE was 0.55, but this value is expected to depend on the environmental conditions to which the plants influence TE.  相似文献   

5.
Insufficient puddling with inappropriate implements or imprecise time/intensity may alter saturated water flow in paddy soil spatially or temporary due to change in aggregate size distribution, dry bulk density, saturated hydraulic conductivity, and percolation rate of the soil. In this study, spatial variability of saturated hydraulic conductivity (K s), a key parameter of the saturated water flow, in Fuchu Honmachi paddy plot (100 m × 28 m) was characterized based on dielectric or ADR dry bulk density (ρb-ADR) with help of non-similar media concept (NSMC) and geostatistics model to meet its correlation to subsurface percolation. A 100 cc core and an ADR data were sampled from each sub-plot (7 m × 7.5 m), and then were used for measuring and predicting ρb and K s. The predicted data agreed with the measured ones, in which they fitted well the x = y line with RMSE of 0.029 cm3 cm−3 (R 2 = 0.68), 0.027 g cm−3 (R 2 = 0.71) (ρb), and 0.098 cm d−1 (R 2 = 0.45) for θ, ρb, and K s, respectively. The predicted ρb and K s had similar trend in spatial variability to the measured ones particularly within the distance of 46.3–51.9 m and 26.2–27.9 m, respectively. The spatial variability of the predicted K s coincided to that of the subsurface percolation rate, in which they had similar distance of dependence. The results indicated that the presenting method can be reasonably accepted.  相似文献   

6.
The objective of this research was to investigate the critical water content (θ c) and water stress coefficient (K s) of soybean plant under deficit irrigation. This research was conducted in a plastic house at the University of Lampung, Sumatra in Indonesia from June to September 2000. The water deficit levels were 0–20%, 20–40%, 40–60%, 60–80%, and 80–100% of available water (AW) deficit, arranged in Randomized Completely Block (RCB) design with four replications. The results showed that the soybean plant started to experience stress from week IV within 40–60% of AW deficit. The fraction of total available water (TAW) that the crop can extract from the root zone without suffering water stress (p) was 0.5 and θc was 0.305 m3 m−3. The values of K s at p=0.5 were 0.78, 0.86, 0.78, and 0.71 from week IV to week VII, respectively. The optimum yield of soybean plant with the highest yield efficiency was reached at 40–60% of AW deficit with an average K s value of 0.78; this level of deficit irrigation could conserve about 10% of the irrigation. The optimum yield of soybean plant was 7.9 g/pot and crop water requirement was 372 mm.  相似文献   

7.
A new coupled model (PCPF–SWMS) was developed for simulating fate and behavior of pollutant in paddy water and paddy soil. The model coupled the PCPF-1, a lumped model simulating pesticide concentrations in paddy water and 1 cm-surface sediment compartment, and the SWMS-2D, a finite element numerical model solving Richard's and advection-dispersion equations for solute transport in soil compartment. The coupling involved improvements on interactions of the water flow and the concentration the pollutant of at the soil interface between both compartments. The monitoring data collected from experimental plots in Tsukuba, Japan in 1998 and 1999 were used to parameterise and calibrate hydraulic functioning, hydrodynamic and hydrodispersive parameters of the paddy soil. The analysis on the hydraulic functioning of paddy soil revealed that the hard pan layer was the key factor controlling percolation rate and tracer transport. Matric potential and tracer monitoring highlighted the evolution of saturated hydraulic conductivity (K S) of hard pan layer during the crop season. K S slightly decreased after puddling by clay clogging and strongly increased after mid term drainage by drying cracks. The model was able to calculate residential time in every soil layers. Residential time of tracer in top saturated layers was evaluated to be less than 40 days. It took 60 days to reach the unsaturated layers below hardpan layer.  相似文献   

8.
Conventional tillage and planting method for rice (Oryza sativa L.) production in northern Iran is wet tillage (puddling). Effect of different puddling intensities on physical properties of a silty clay soil (Typic Haplodalfs) was investigated under laboratory and field conditions. Changes in soil physical parameters and water requirement for puddling were measured. For laboratory experiments, undisturbed cylindrical soil samples (diameter and height of 50 cm), were used. A laboratory puddling apparatus was designed and constructed. The puddling intensity was measured by duration of puddling. Four levels of puddling intensity were used as: P 0 (no puddling, control), P 1 (low), P 2 (medium) and P 3 (high). For field tests, 12 plots of 8 × 4 m were selected. The first tillage was performed with a moldboard plow and then the plots were puddled with different intensity using a rotary tiller. The results showed that under laboratory conditions, water content of the puddled layers decreased with an increase in settling time. During drying period, P 0 dried faster than P 1, P 2 and P 3. Puddling with low intensity in laboratory and field conditions caused bulk density of 0–15 cm soil layer to decrease by 24.07 and 25.45%, respectively. Increasing puddling intensity increased the bulk density. Bulk density increased with time as particles settled after halting the puddling. Bulk density increased with depth as well. Under laboratory conditions, increasing puddling intensity from P 1 to P 2 reduced percolation rate significantly. For all puddling intensities, soil moisture characteristic curves of both field and laboratory samples showed that puddling increased the amount of water retained over the whole range of suctions. More water was needed for P 3 as compared to P 1 and P 2. Under the laboratory and field conditions, the P 3 required 27.72 and 28.58% more water as compared to P 2, respectively. Although the mechanisms implemented for puddling were different under laboratory and field experiments, the results were similar. Bulk density, soil moisture content and water percolation rate decreased faster in the puddled soil under field and laboratory conditions. Therefore, to reduce the cost and time, the laboratory method could be used to study the effects of puddling intensity on physical properties of paddy soils. Medium intensity puddling was shown to be the proper tillage practice for paddy fields with silty clay soil.  相似文献   

9.
The objective of this research was to investigate the effect of water stress in regulated deficit irrigation (RDI) on the yield of soybean growing on Ultisol soil. This research was conducted under plastic house on the experimental farm of Lampung Polytechnique from August to November 2004. The water stress treatments in regulated deficit irrigation were ET1 (1.0 × ETc), ET2 (0.8 × ETc), ET3 (0.6 × ETc), ET4 (0.4 × ETc) and ET5 (0.2 × ETc), arranged in a randomized block design with four replications. ETc means crop evapotranspiration under standard condition, which was well watered. For example, the ET2 (0.8 × ETc) treatment means that the amount of supplied water per a day is the same as the crop adjustment evapotranspiration (ETcadj) with the value 0.8 of water stress coefficient (K s). The RDI treatments were carried out just at vegetative phase and its treatments were stopped at the beginning of flowering phase, and afterwards the treatments were watered at 1.0 × ETc. The results showed that since week II, the soybean experienced stress throughout the growth period except ET2 treatment. ET2 treatment started to be stressed at week V and continued to be stressed until the harvest time. At the ET3 treatment, the critical water content (θc) of soybean was reached at week II, and the θc was 0.24 m3/m3 on the average. The RDI at vegetative period significantly affected the yield. The highest yield was ET1 (35.2 g/plant), followed by ET2 (31.0 g/plant), ET3 (18.1 g/plant), ET4 (7.6 g/plant), and ET5 (3.3 g/plant). The optimal water management of soybean with the highest yield efficiency was regulated deficit irrigation with water stress coefficient (K s) of 0.80 for vegetative phase.  相似文献   

10.
《Plant Production Science》2013,16(4):333-341
Abstract: The need for solar radiation (Rs, MJ m–2 d–1) estimation remains a common concern for agronomists. Evaluation of crop productivity is primarily based on Rs data, which are difficult to collect because of cost and calibration requirements. Generally, historical Rs data are more difficult to obtain. This study focused on an estimation model based on the daily range of temperature and evaluated its accuracy from the viewpoint of crop productivity analysis. The variability of an empirical coefficient in the model (Krs), which was derived from the relation between Rs and daily range of temperature (Tmax – Tmin) was analyzed using climatic data observed in Japan considering data availability and quality. Krs had significant monthly differences, and it significantly increased from 1981 – 1985 to 2003 – 2007 at all 10 locations. Period-month interactions were not significant, except for in Utsunomiya, suggesting that the seasonal pattern did not change during the period. Weather data indicated that the increase in Krs was caused not only by increased solar radiation but also by a decrease in Tmax – Tmin. The substantial differences in Krs produced considerable bias for the estimated Rs when the estimation was conducted with a constant Krs (0.16). Despite the bias, the model is considered to perform well given the present availability of Rs data. The results of this study suggest that the evaluation of the seasonal pattern of Krs greatly improves the model accuracy.  相似文献   

11.
Paddy fields are subjected to fluctuating water regimes as a result of the alternate drying and wetting water management, which often incurs a sensitive change in N2O emissions from paddy soils. However, how the soil moisture regulates the emission of N2O from paddy soil remains uncertain. In this study, three incubation experiments were designed to study the effects of constant and fluctuating soil moisture on N2O emission and the sources of N2O emission from paddy soil. Results showed that the N2O emission from paddy soil at 100 % WHC (water-holding capacity) was higher than that at 40, 65, 80, 120, and 160 % WHC, indicating that 100 % WHC was the optimum soil moisture content for N2O emission under the incubation experiment. Small peak of N2O flux appeared when the soil moisture content from 250 % WHC decreased near to 100 % WHC, lower than that triggered by nitrogen (N) fertilization, which was mainly owing to the low NH4 + concentration at this period. Nitrification dominated the emissions of N2O from paddy soil at 250 % WHC (54.96 %), higher than that of nitrification-coupled denitrification (6.74 %) and denitrification (38.3 %). The contribution of denitrification to N2O emissions (44.10 %) was equivalent to that of nitrification (44.45 %) in soil at 100 % WHC, which was higher than that of 250 % WHC treatment. In conclusion, the finding suggested that the peak of N2O in paddy soils during midseason aeration could be attributed to the occurrence of optimum soil moisture under sufficient N availability, favorable for the production and accumulation of N2O.  相似文献   

12.
ABSTRACT

Oil pollution is a worldwide threat to the environment that affects the development of plants. The effect of soil contaminated by diesel on the physiological responses of seedlings of Quercus oleoides was investigated in two independent experiments. We proposed that physiological performance will decrease when seedlings are exposed to higher concentration of contamination. At the first experiment, levels of pollution with diesel were of 0%, 5%, 10% and 15%, and 0%, 2% and 3.5% in the second one. In the first experiment, photosynthetic rate, stomatal conductance, transpiration and total chlorophyll of Q. oleoides were higher in the control seedling, and lower in treatments of pollution with 5%, 10% and 15% of diesel during 3 days of treatment. Only, seedlings in soil polluted with 5% of diesel survived up to 16 days; they showed a photosynthetic rate of 5 μmol m?2 s?1, which was lower than control seedlings (9 μmol m?2 s?1). This pattern was observed in stomatal conductance, transpiration and relative water content. Surprisingly, in the second experiment, seedlings showed a higher photosynthetic rate and growth at 2% of diesel-contaminated soil than control seedlings, a phenomenon known as hormesis. In both experiments, soil respiration was proportional to soils contaminated. We concluded that Q. oleoides is highly vulnerable in soils contaminated with above 5% of diesel, but it maintains its physiological activities in soils contaminated below 2%, suggesting that seedlings can grow under low concentration of diesel contaminant, and may be used in phytoremediation of soils with low concentrations of diesel contamination.  相似文献   

13.
One of the options to ameliorate the deleterious effects of sodic water irrigation is to apply gypsum to soil. We examined whether the application of organic manures or crop residue can reduce the need for gypsum in calcareous soils. A long-term field experiment with annual rice-wheat cropping rotation was conducted for 15 years (1991-2006) on a non-saline calcareous sandy loam soil (Typic Ustochrept) in northwestern, India. The irrigation water treatments included good quality canal water (CW) and sodic water (SW) with residual sodium carbonate (RSC) of 10 mmolc L−1 from 1991 to 1999 and of 12.5 mmolc L−1 from 2000 onwards. Gypsum was applied at 0, 12.5, 25, and 50% of the gypsum requirement (GR), to neutralize RSC of the SW. Three organic material treatments consisted of application of farmyard manure (FYM) at 20 Mg ha−1, Sesbania green manure (GM) at 20 Mg ha−1, and wheat straw (WS) at 6 Mg ha−1. The organic materials were applied every year to the rice crop. Continuous irrigation with sodic water for 15 years without gypsum or organic materials resulted in a gradual increase in soil pH and exchangeable sodium percentage (ESP), deterioration of soil physical properties, and decrease in yields of both rice and wheat. The cumulative yield loss in SW irrigated plots without gypsum and organic materials remained <1.5 Mg ha−1 for up to eight years in the case of rice and up to nine years in the case of wheat. Thereafter, marked increase in pH and ESP resulted in further depression in yields of rice by 1.6 Mg ha−1 year−1 and wheat by 1.2 Mg ha−1 year−1. Application of gypsum improved physical and chemical properties of the soil. The beneficial effects on crop yields were visible up to 12.5% GR in rice and up to 50% GR in wheat in most of the years. All the organic materials proved effective in mobilizing Ca2+ from inherent and precipitated CaCO3 resulting in decline in soil pH and ESP, increase in infiltration rate, and a increase in the yields of rice and wheat crops. Although the application of organic materials resulted in comparable reductions in pH and ESP, the increase in yield with SW was higher for both crops with FYM. Pooled over the last six years (2000-2006), application of FYM resulted in 38 and 26% increase in rice and wheat yields, respectively, over SW treatment; corresponding increases in 50% GR treatment (recommended level) was 18 and 19%. During these years, application of GM and WS increased wheat yields by 20%; for rice, GM resulted in 22% increase compared to 17% in WS amended SW irrigated plots. Combined application of gypsum and organic materials did not increase the yields further particularly in the case of FYM and GM treated plots. This long-term study proves that organic materials alone can be used to solubilize Ca from inherent and precipitated CaCO3 in calcareous soils for achieving sustainable yields in sodic water irrigated rice-wheat grown in annual rotation. The results can help reduce the dependency on gypsum in sodic water irrigated calcareous soils.  相似文献   

14.
研究土壤水分、玉米光合特性及产量对秸秆不同还田耕作技术的响应,为半湿润区水分、光能高效利用及玉米增产栽培模式提供理论依据。2018和2019年,采用秸秆还田和土壤耕作相结合的方法,设置秸秆离田旋耕起垄（CK）、秸秆深翻还田（SP）、免耕秸秆覆盖还田（SC）、秸秆覆盖深松（SS）4个处理。研究结果表明,2018和2019年各生育时期土壤含水率、叶面积指数、叶片的Pn、Gs、Ci和Tr,SS处理均显著高于CK处理。与CK相比,SS、SP、SC处理2018和2019年的玉米产量分别增加13.88%和14.82%、7.59%和9.12%、7.42%和8.5%。秸秆条带覆盖深松技术适合作为半湿润区水分、光能高效利用和玉米增产的一种优化栽培技术进行推广应用。  相似文献   

15.
Investigation on dimensional stability of cotton plain weft knitted fabric manufactured from rotor spun yarn, subjected to mercerization treatment has been represented. Several fabric samples were mercerized considering variation in time of treatment, bath temperature, concentration of alkali solution and also mercerizing tension. Values of constant of course (K c ), constant of wale (K w ), the area geometry constant (K s ) which are indicative of fabric dimensional stability were calculated after treatment for mercerized samples. Then, these values were compared with those of un-treated samples subjected to dry and wet relaxation and also were compared with each other. Based on the effect of each variable itself and their simultaneous effect, it was concluded that, mercerization treatment and considered parameters had a distinctive influence on dimensional stability of the fabric. Mercerized samples had better dimensional stability in comparison with un-treated ones. A comprehensive experimental analysis showed that, there is meaningful difference between K s values of the samples mercerized at various conditions. Also, the area geometry constant (K s ) achieved after treatment was higher than that of other relaxation methods.  相似文献   

16.
Liquid treatments to accelerate drying were applied to lucerne under laboratory conditions by brief immersion (～3s) of cut shoots. Aqueous solutions of the alkali metal carbonates Li2CO3, Na2CO3 and K2CO3 were found to reduce drying times to 33% moisture content (MC) on a dry weight basis (dwb) by 45%, 55% and 65% respectively. Effectiveness was related to the ionic radius of the cation. From a range of potassium salts (KCl, K2CO3, KHSO4, KOH, K2SO4) in aqueous solution, the only useful reductions in drying time to 33% MC (dwb) came from the alkaline KOH (68%) and K2CO3 (65–76%). It is considered that K+ has a specific function in increasing water loss through the plant cuticle and that association with CO32- provides the high pH necessary for this activity. An aqueous solution of K2CO3 (0·16 M) gave greater acceleration of drying than the organic solvent petroleum ether and no benefit was gained by combining these treatments. Addition of a surfactant did not improve the effectiveness of K2CO3 as a desiccant but mixing with a rape-seed oil emulsion reduced the drying time to 33% MC (dwb) by 11% relative to K2CO3 alone. Under field conditions K2CO3 as an aqueous solution gave only small reductions in the drying time to 33% MC and effectiveness was reduced by the addition of the rapeseed oil emulsion. Better results with K2CO3 (aq) might have been achieved with a more ventilated swath structure but the results strongly suggest that the oilseed rape emulsion is unlikely to improve the effectiveness of K2CO3 under field conditions.  相似文献   

17.
A two year experiment was carried out in newly reclaimed soils (sandy soils) to investigate the effect of cutting and phosphorus and potassium fertilization on the growth, yield, seed mucilage content and seed protein content of guar plant. The results revealed that different cutting treatments significantly decreased the plant weight, seed yield, seed mucilage content and seed protein content. Phosphorus fertilization up to 350 kg super-phosphate (15% P2O5)/feddan significantly increased plant weight, seed yield, seed mucilage content and seed protein content. Fertilization with 150 kg potassium sulfate (48% K2O)/feddan was quite capable to meet guar plant potassium demands in this kind of soil. Without cutting plants, fertilization with 350 kg superphosphate and 150 kg potassium sulfate/feddan resulted in the highest seed yield, seed muculage content and seed protein content.  相似文献   

18.
The micro paddy lysimeter (MPL) was developed and evaluated for its performance to simulate solute transport in paddy environment under laboratory conditions. MPLs were constructed using soil collected from Field Museum Honmachi of Tokyo University of Agriculture and Technology, Japan. For the physical characteristics of the hardpan layer, parameters such as thickness, and soil aggregate size, affecting the percolation rate were studied. For the plow layer, two types of plow soils, sieved and un-sieved soils were compared. The sieved soil plow layer was produced by mixing air-dried soils of different aggregate sizes of D > 9.50, 9.50 ≥ D > 4.75, 4.75 ≥ D > 2.0 mm and D ≤ 2.0 mm at 47.1, 19.5, 20.6, and 12.8%, respectively. The un-sieved plow layer soil was directly used after collecting from the field. Inert tracer was applied to ponding water with controlled boundary conditions to evaluate the reproducibility of the soil hydraulic characteristics. HYDRUS-1D was used to evaluate the movement of bromide tracer in the MPL. The proposed conditions of the MPL were that the hardpan layer can be made from soil aggregates smaller than 0.425 mm with 2 cm thickness and that the plow layer can be prepared with sieved or un-sieved soils. With these conditions, the obtained results proved that MPLs can be a useful tool to simulate solute transport in paddy environment.  相似文献   

19.
Summary The response of five potato cultivars (Alpha, Cardinal, Désirée, Spunta and Up-to-Date) to a range of amounts of irrigation nitrogen top dressing (N.t.) in a rainless region was studied by means of the line-source sprinkler method. The irrigation-to-evaporation ratio,K p, ranged from 0.14 to 1.27 and N.t. from 12 kg/ha to 201 kg/ha, respectively. In all cultivars, the yield increased linearly up toK p=1.0; at higher ratios there was a yield decline in all cultivars except for Cardinal, in which the yield function flattened off. Spunta was the highest yielding cultivar (16t/ha) in the dry range (K p=0.14; N.t.=12 kg/ha). Désirée was the highest yielding cultivar (64 t/ha) in the wet range (K p=1.0; N.t.=201 kg/ha), and Alpha was the lowest yielding cultivar in both the dry and wet range (9 and 46 t/ha, respectively). Leaf permeability, leaf water potential and photosynthesis rate decreased, and tuber dry matter percentage increased with decreasingK p: these indices also varied with plant age, and among cultivars. Yields were adversely affected when soil water potential at the 30-cm depth dropped below −0.4 bar. Contributon from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel. No E-811, 1983 Series.  相似文献   

20.
Based on data collected from rice fields under drying–wetting cycle condition, the procedure of dual-crop coefficient (K cd) approaches was calibrated and validated to reveal its feasibility and improve its performance in rice evapotranspiration (ET c) estimation. It was found that K cd based on FAO-recommended basal crop coefficients (K cb) underestimated dual-crop coefficients in monsoon climate region in East China. The recommended coefficient (K cp) value of 1.2 was not high enough to reflect the pulse increase of rice ET c after soil wetting. The K cb values were calibrated as 1.52 and 0.63 in midseason and late season, and the K cp value was adjusted as 1.29 after soil wetting in rice field under drying–wetting cycle condition. The dual-crop coefficient curves based on locally calibrated K cbCal and K cpCor matched well with the measured crop coefficients and performed well in calculating rice evapotranspiration from paddy fields under drying–wetting cycle condition. So it can be concluded that the procedure of dual-crop coefficient method is feasible in rice ET c estimation, and locally calibrated K cb and K cp can improve its performance remarkably.  相似文献   

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