جستجوی مقالات مرتبط با کلیدواژه « gdd » در نشریات گروه « آب و خاک »

Improving soil water situation in the paddies by subsurface drainage systems provides suitable condition for the cultivation of winter canola. In order to evaluate the effect of subsurface drainage on the winter canola growth in paddy fields, an experiment was conducted as split plot in a randomized complete block design with three replications. The main factor involved farm drainage system consists of three conventional drainage systems with 0.90 m and 0.65m depths at 15 and 30m distances (D0.90L30, D0.65L30 and D0.65L15: D and L indicate drain depth and spacing, respectively) and a subsurface drainage system with four drain lines spaced 15 m apart with a depth of 0.65 m and 0.90 m as alternate (Bilevel). The sub factors were also the days after planting. During the growing period, to determine leaf area index (LAI), 1326 canola leaves were sampled and were analyzed by direct measurement and Digimizer software. The DataFit9 software was applied to examine the mathematical equations governing the canola LAI under different drainage systems. Water table rising was affected by precipitation and its falling was related to the performance of different subsurface drainage systems. In this regard, Bilevel system with mean depth to the water table of 64.7 cm had higherLAI. Critical LAI was found in 100 to 114 day after planting and its maximum (4.71) was observed in Bilevel. Even mathematical functions with the orders of 6 and 8 showed more accurate estimation other than equations for LAI in different drainage systems. Base on the results, subsurface drainage with proper depth and spacing could improve canola LAI by controlling the water table below the root zone.

The aim of this study was to investigate the climate change impacts on some factors affecting rainfed wheat growth such as effective rainfall, planting date and length of growing season in four stations located in Chaharmahal and Bakhtiari province. Firstly, it is necessary to predict future (2046-2065) climatic conditions. For this purpose, the output of HADCM3 general circulation model was used under three scenarios of A1B, A2 and B1. The data were downscaled by LARS-WG model. After simulating the climatic parameters in mention period, the effective rainfall during the wheat growing season was calculated by Food and Agriculture Organization method. Also, the optimum planting date was defined according to the date of the first rain (at least 10 mm in case of continuing for next days). The wheat's growth stages were determined by Growing Degree Days method. The results indicated a rise in temperature for four stations. On average, it is expected that the annual temperature increase by 1.8°C compared with the baseline period (2010-1990). Total annual precipitation in Shahrekord, Koohrang and Borujen will decrease 2.2, 7.8 and 3.6 per cent respectively. About Lordegan it will increase by 2.7 per cent. Also, the results showed that in three stations of Shahrekord, Koohrang and Borujen, the amount of effective rainfall in November will increase compared to baseline, but in Lordegan it will reduce. So, in the first three stations, in most years, planting date was obtained earlier than baseline, but in Lordegan it was later than baseline. The Length of growing season will reduce in Shahrekord, Borujen and Lordegan stations, 12 days on average and in Koohrang about 13 days.

Determination of chilling and heating requirements is an important process for selecting fruit trees specifically adapted to climatic regions. In this study, the thermal thresholds of different phenological stages of apple tree (Red Delicious variety) were determined for further analysis. Long-term hourly and daily temperature data from 1985 to 2014 of Karaj station were collected and used for running three chilling requirement models namely CH, UTAH and CP. The results showed that the chilling requirement of this late variety is not satisfied. A significant decreasing trend in accumulated chilling units was observed. Application of growing degree days (GDD) model confirmed that the required heat units are maintained without limitation. The findings revealed that there exists a significant decreasing trend in occurrence date of phenological stages which might be due to higher temperature during the season. These conditions (earlier onset of vulnerable reproductive phases) increase the risk of frost and chilling damage. In most phenological stages of the apple tree, the mean air temperature showed an increasing trend. According to the results, late varieties are not suitable for current climatic conditions of Karaj climate and should be replaced with early ones. Further agroclimatic studies are recommended for more scrutiny across the country considering the sequences of global warming.

Most In this research, the ability of HYDRUS2D and ANFIS models for simulating temporal variations of soil water content and soil water balance components under full irrigation and water deficit irrigation with two levels of 75 and 55 percentage in a maize field were compared to determine water stress duration in the growing season. To do so, soil water content was measured using TRIME-FM TDR sensors during two growing seasons for calibrating and validating HYDRUS2D model. Also, soil water content was simulated using ANFIS with different type of membership functions and using independent variables of days after planting, GDD, irrigation depth and water stress level. Comparing root mean square error, mean bias error and model efficiency coefficient indices for simulating soil water content stress period duration, soil water content and soil water balance components demonstrated the possibility of using ANFIS instead of a complicated model such as HYDRUS2D when defining the suitable independent variables. Despite 10 days sooner application of treatments in second growing season, the same water stress duration under DI75 treatment for both growing season (i.e. since 82 DAP till harvest) shows that it is possible to apply treatments either sooner or with higher intensity when applying deficit irrigation. Based on the results, ANFIS model could be used for these purposes.