جستجوی مقالات مرتبط با کلیدواژه "کشت دیم" در نشریات گروه "آب و خاک"

Most of the studies that have been conducted in order to investigate the pattern of temporal and spatial changes of rainfall in rainfed areas have finally resulted in determining the trend of total annual, seasonal, and monthly rainfall in the target areas. However, changes in the frequency and intensity of rainfall are among the important parameters that have a great impact on the trend of rainfall and the planning of rainfed areas. The purpose of this study is to investigate the effect of changes in the frequency and intensity of daily rainfall on the trend of annual and seasonal rainfall in Kurdistan province.

For this purpose, the rainfall data of 30 years (1988 to 2017) of four synoptic stations of Sanandaj, Bijar, Qorveh, and Saqez, located in Kurdistan province, were used. After the data homogeneity test, the trend of changes in time series of frequency and amount of rainfall was calculated through the non-parametric Mann-Kendall test and Sen's slope estimator.

 The obtained results indicated a decreasing trend between 25 and 31% of total annual rainfall compared to the average of the studied period in four stations and this decrease was related to spring, summer, and winter seasons in most cases. The rainfall trend did not change significantly in the autumn season. Even though the trend of the rainy days in Sanandaj and Qorveh stations had a significant increase of 0.54 and 0.63 days per year, respectively, the results showed that this increase was related to spring rains which have had less intensity than five millimeters per day and cannot be very effective in providing water requirement. The noteworthy point was that the intensity of rainfall has decreased in all stations which is the main reason for the more than 40% decrease in the amount of rainfall during the spring and winter seasons of Sanandaj, Qorveh, and Saqez stations.

In general, increasing the frequency of low-intensity rains and decreasing the intensity of rains in rainfed areas can be a serious threat to reducing yield. Therefore, it is necessary to investigate the changes in the frequency and intensity of rainfall, along with its values, in order to determine the distribution pattern of annual and seasonal rainfall in rainfed areas.

Wheat, as one of the most important crops in Iran and all around the world, has taken a significant share of the area under cultivation and production. The lack of water resources in the dry climate of Iran makes it necessary to use the available water resources to the optimal level. The analysis of optimal water consumption in agricultural production is done by using the water efficiency index. In this study, rainwater productivity in rainfed wheat cultivation in Kurdistan province was estimated using the AquaCrop-GIS model. Performance information was collected from the Agricultural Products Insurance Fund in the six-year period from 2014-2015 to 2019-2020. Also, information from synoptic meteorological stations and the global soil data bank were used for the required basic information. The model results show a 90% agreement index in the simulation process. Also, according to the average water productivity index calculated by the model, a zoning map of the areas prone to rainfed wheat cultivation was presented. Kamyaran district, having an average water productivity index of 0.68 kg/m3, was identified as the most suitable part of the province for dry wheat cultivation. According to the special conditions of Kurdistan province, it is suggested that the development of the cultivated area should be done according to the priority of more susceptible areas and based on the rainwater productivity index in the province.

For proper management of soil, conducting a comprehensive assessment seems necessary and basic. Soil forming processes strongly vary among different land uses and topographies. In this study, a factorial experiment was performed in a completely randomized design with 2 factors (type of land use and soil depth) in 3 replications, in order to investigate the impacts of topography and different land uses on soil physical, chemical and mineralogical properties of soils of Chaypare, West Azerbaijan province, Iran. There were three dominant land uses including pasture (low density of vegetation cover), dry farming (mainly wheat without annual alternating crops) and irrigated farming (with annual alternating crops). In the present study, two soil profiles were dug for each land use and then clay mineralogy, along with the physico-chemical properties, were determined. The results indicated that changes in the both topography and land use influenced the soil cation exchange capacity (CEC) through affecting both the clay and soil organic matter contents. Although, there were no significant differences in physic-chemical properties among different land uses, the soils of irrigated farming showed relatively lower amounts of calcium carbonate equivalent (CCE) and sand content than the two other land uses and the amounts of organic matter content and CCE and pH were considerably dominant in the irrigated farming. The X-ray diffraction (XRD) measurements indicated that both the topography and type of land use had no significant effect on the qualitative properties of the clay minerals but they were effective on their semi-quantitative properties. Accordingly, the amount of smectite in the fine clay fraction in the irrigated farming was dominantly higher than that of the other land uses. Additionally, the status of the different cultivated crops seemed to affect the quantity of clay minerals in the both dry and irrigated farming land uses. Finally, the irrigated farming compared with the two other land uses (pasture and dry farming), revealed to be more affected by the slope and pedogenic processes.

Soil infiltration rate is the major soil hydraulic property which can be affected by the soil physical characteristics and management practices. The use of land can affect various soil properties such as physical and hydraulic properties. Differences of the hydraulic soil characteristics such as infiltration rate in various land uses can affect their potential to runoff production as well as soil loss in the catchment. The knowledge of the physical and hydraulic characteristics of various land uses can help to better management of soil and water in the catchment. It is very essential in the semi-arid catchments where vegetation cover is generally poor, the soils are often instable against erosive factors especially when the rainfalls are consecutive and intensive. Therefore, this study was conducted to investigate the soil physical and hydraulic characteristics in the TahamChai catchment, in a semi-arid region, NW Zanjan. Various land uses consist of pastures, rainfed and irrigated lands can be observed in the catchment, which cover about 62%, 33%, and 5% of the catchment area, respectively. The pastures have been covered with poor vegetation and are intensively exhausted by over-grazing. Rainfed lands are mostly under winter wheat cultivation. Soil erosion and sedimentation were the major environmental problem in this catchment.
The maps of land use and slope gradient were provided for study area. A total of 20 sites were selected based on the surface area of each land use in the catchment located between 34 46-36 53 N latitudes and 48 17-48 37 E longitudes. The study area consisted of ten sites in the pasture, seven sites in the rainfed and three sites in the irrigated lands. The geographical positions of study sites were determined by a global positing system (GPS). Soil infiltration rates were measured by double rings method at three replications in each site. Variation of soil infiltration rate was determined for each land use. Soil samples were collected at three replications from each site to determine other physicochemical soil properties. Particle size distribution, bulk density, saturation percentage, aggregate mean weight diameter, organic matter, and equivalent calcium carbonate were determined using standard methods in the lab. Mean comparisons of infiltration rate along with other physicochemical soil properties among the land uses were done using the Duncan's parametric method. The Pearson’s correlation coefficients were used to determine the relationships between soil properties and soil infiltration rate.
Based on the results, no significant difference was observed between the land uses in particle size distribution. Soil infiltration rate showed different patterns among the land uses, so that significant difference was observed among them (p Pastures with poor vegetation cover appeared the lowest soil infiltration capacity as compared to other land uses in the catchment. Decreasing soil infiltration rate was associated with increasing bulk density in the area. It seems that overgrazing in the pastures increases soil bulk density and leads to decline the soil organic matter content as well as soil aggregation and aggregate stability. According to the results, pastures have the highest potential to runoff production and soil erosion rather than the other land uses (rainfed lands and irrigated lands). Therefore, maintaining vegetation cover and preventing over-grazing in the catchment is recommended to increase soil organic matter content and decrease soil compaction. These practices improve the hydraulic soil characteristics especially infiltration rate and in consequence decrease the catchment potential to runoff production and soil erosion.

Water shortages has always been a great concern as a limiting factor for agricultura l production in Kerman province. Rainfed sowing may be recommended to bypass the problem. Because of high rates of potential evapotranspiration and limited water resources in arid and semiarid areas, it is expected more attention will be paid to study of the effects of rain fed culture on quality of medicinal plants. In order to investigate the establishment, growth and yield of some of perennial medicinal plants (Thymus caramanicus, Elaeagnus angustifolia, Olea europaeain, Thymus vulgaris, Rosa damascena, Thymus daenensis, Artemisia persica, Ferula assa feotida, Glycyrrhiza glabra, Rosmarinus officinalis, Lavandula officinalis, Salvia officinalis, Achillea millefolium ), the study was conducted using a randomized complete block design (RCBD) with 3 repli cations during 3 years from 2012 to 2014 in the Kohpanj mountains in the west of Bardsir city. During the growing seasons, the phonological and morphological events were recorded and finally analyzed by SAS software and the means were compared using Dunca n's Multiple Range Test at 0.05 level. The results showed Thymus caramanicus, Elaeagnus angustifolia and Olea europaeain destroyed in the first summer because of environmental drought. Thymus vulgaris, Rosmarinus officinalis, lavandula officinalis, Achille a millefolium and Salvia officinalis Survived in the first year, but destroyed in the second year. Rosa damascena 85%), Thymus daenensis (60%), Artemisia persica (77%), Ferula assa feotida (100%) and Glycyrrhiza glabra (100%) had the most survival rate am ong the species. With aging, dry weight of the plants were increased. The greatest dry weights were in Thymus daenensis, Artemisia persica and Ferula assa feotida respectively equal 188, 135.6 and 16 g/m 2 . The greatest dry weight of root in Glycyrrhiza gl abra (173.3 g/m 2) obtaind in the third year. The most number of flowers in Rosa damascena (31 flowers per plant) obtained in the third year.

Classification in terms of climate and hydrological variables is one of the basic requirements in water resource planning. The same climate characteristics in the different geographical areas causes that climate scientists, separate the areas with the same climate and put the zones in one group that have similar features. Cluster analysis is one of the multivariable statistical methods that is used to reduce the data and finding homogeneous regions. Principle component analysis (PCA) is one of the multivariable statistical methods that is done by analyzing the eigenvalues of correlation or covariance matrix. The purpose of these methods regionalization or zoning and extending point information to an area which resulted in providing the information for the zones or stations without information or with insufficient information. Evaporation as output of water resources and contrary to that, precipitation, is considered as input of water resources. Then the ratio of these two variables in the given time scale (e.g., monthly) can express the climatic condition of the area in terms of dryness so whatever the rainfall is greater than evaporation, can represent the wetness of the area and success of dry farming. In addition to the total annual rainfall in dry farming, the distribution of rainfall during the period of growth is the important parameter. Existence of enough moisture in the process of budding is necessary for growth and plant establishment. Also in the spring, which coincides with the flowering and grain growth, due to the warming weather and increasing evapotranspiration, plant water requirement increased. Rainfall in these periods could have significant influence in the crop growth and production.
In this study, in order to investigate the capability of northwest of Iran for dry farming this area was delineated based on the ratio of precipitation to evapotranspiration. For this purpose, the climatic parameters of 22 synoptic and climatology stations of were used during the period from 2000 to 2006. The average evapotranspiration for each station was determined by FAO-Penman-Monteith method and by using the monthly precipitation data, the ratio of precipitation to evapotranspiration was calculated. The missing data were reconstructed by the program written in the FORTRAN programming. The principal component analysis was done by MINITAB software and correlation matrix. Then, by using the scree plot, the first up to fourth factors with high eigenvalues were selected for zoning. In the next step, the same coefficient curves for every selected component, drawn on the map of the study area and the homogeneous regions were specified based on the ratio of precipitation to evapotranspiration. Finally the delineated areas were simultaneously drawn on a map.
Then, by principle component analysis method and six selected principal components after rotation that contain 74.1 percent of data's variance, six homogenous regions based on the ratio of precipitation to evapotranspiration were introduced among which the second region with the mean ratio of precipitation to evapotranspiration equal to 0.5, has the highest priority of the dry farming. By using the WARD method and drawing dendrogam, two homogenous regions were achieved that in autumn, the second region with the value equal to 0.49 of precipitation to evapotranspiration and in spring, the first region with the value equal to 0.59 for mentioned parameter were in the priority of dry farming. By using the S-statistic method, cluster's homogeneity test was performed which was significant at the level of 5%. The F-test between the standard deviation of zones in the WARD method, showed a significant difference between them so that the ratio of the standard deviation (2.68) was obtained greater than the critical value (2.57). Therefore, with respect to the quality of the zone's separation and clustering data expansion, the WARD method was selected. The south of East Azarbaijan Province, has the lowest amount of precipitation to evapotranspiration, in case of appearing water shortage in this area, agriculture and horticulture will be in serious threats so that requires prior planning and appropriate actions. Finally, it can be said that the mentioned method can be used as a guide for proper management and optimal water resources operation on a large scale, such as in the basin or province. Moreover, by using this method, critical areas of water resources can be detected easier and the appropriate coping plans can be prepared to avoid serious damages to farmers of those areas.

Climate condition is one of the most important factors which affect agricultural production. Amongst climate parameters, rainfall variability is one of the most crucial factors which has important role on agricultural productions because of its effect on available water for plants. The amount of water available to plants strongly depends on the rainy seasons onset, length and rainfall temporal distribution, hence can determine a success or failure of a growth season. One of the most important areas for crops production in Golestan province is the Aq-Qalla township. Most of the areas are used for rainfed farming, such as wheat and barely. In general, agriculture in Aq-Qalla township is dependent on rainfall. Determination of the precipitation spatial variability in these agricultural lands is particularly very importance. Therefore, the objectives of this research were the investigation of different interpolation methods for estimation and zoning of precipitation variables in agricultural lands of Aq Qalla township for rainfed cropping of autumn cereals. Also, this research provides information at local level that could be used by farmers to increase of yield in rainfed condition.
In this research, the spatial distribution of precipitation on agricultural lands of Aq-Qalla township evaluated using 18 method-models from deterministic and geostatistic interpolation such as, Inverse Distance Weighted (IDW), Universal Kriging (UK), Ordinary Kriging (OK), Radial Basis Function (RBF) and Local Polynomial Interpolation (LPI). The performance criteria for evaluation were Root Mean Square Error (RMSE) and General Standard Deviation (GSD) with the Cross Validation methods.
The results showed that Local Polynomial Interpolation (1 and 2 degree) was the best method to estimate precipitation parameters except spring and June precipitation. Because, it had the highest accuracy and the lowest error for estimating of these parameters. Semivariograms analysis indicated that annual and June precipitation were best fitted to Exponential model, also, autumn, spring and May precipitation by Spherical model. Results of final maps showed that amount of annual, autumn and June rainfall were lower in north than south regions. Moreover, the results of this research showed that about 65.62 percentage of agricultural lands of Aq-Qalla had suitable level of annual rainfall (300-400 mm). Also, in this area amount autumn rainfall was 101.11 to 166.08 mm.
The results indicated that same as temperature requirements, the annual and autumn rainfall requirements of current crops such as wheat and barley are provided in this township. But, amount of spring and June rainfall are non-suitable in this area. Wide area in Aq-Qalla township were under 10 mm rainfall in June. This amount is not enough for grain filling.

Leaf Wetness Duration (LWD) is a key parameter in agricultural meteorology. Because of difficulties involved in LWD being readily measured, several methods have been developed to estimate it from weather data. Among the employed to estimate LWD, those that use physical principles of dew formation plus dew and/or rain evaporation have shown to be especially transmittable and of sufficiently accurate results, but their complexity is a disadvantage for operational use. Alternatively, empirical models have been utilized despite their limitations. The simplest empirical models use only relative humidity data. The objective of this study was to evaluate the performance of an RH-based empirical model and a Penman-Monteith physical model to estimate LWD in Sarvestan automatic station located in Fars province. The results indicated that both models during warm seasons underestimate LWD, while during cold seasons, the physical and empirical models show overestimation and underestimation, respectively. The Mean Absolute Error (MAE) in empirical model was recorded to be less than that in physical model's estimations. An adjusted optimum threshold value of relative humidity was suggested for the study which improved the estimations. Using an RH-based empirical model led to more accurate LWD estimations with less errors as compared with the previous published data. Hourly comparisons also showed that the optimum threshold model was of a more acceptable performance as compared with the other models.

The use of suitable empirical models for estimation of soil erosion and sediment yield is essential because of nonexistence or shortage of associated data in many watersheds. In the present study, the applicability of the USLE and its different versions Viz. MUSLE-S, AOF, MUSLT, MUSLE-E, USLE-M and AUSLE in estimation of storm-wise sediment yield from standard plots installed in dry farming, ploughed and rangeland treatments was evaluated. To conduct the study, the entire input data were collected from plots installed in three replicates in each treatment in Khosbijan Natural Resources Research Station in Arak Township. The models’ estimates were then compared with the observed sediment data for 12 storm events. Contrary to high correlation among different models’ estimates, the models used in estimation of measured sediment data were found inapplicable. However, significant relationship (r=94.4%) and non-significant relationship with correlation coefficients less than 50% were found between MUSLE-E, and MUSLE-S and MUSLE-E estimates and measured data in rangeland, dry farming and ploughed treatments, respectively.