عنوان مقاله [English]
Rice is one of the most important agricultural products in the world, which ranks second after wheat in terms of annual production and is the main food of half of the world's population although rice is cultivated in a wide range of climatic conditions and altitude, but this plant is vulnerable to changes in environmental conditions Growth condition of rice plant and climatic conditions and characteristics affect its yield and suitable planting date according to the existing environmental factors to prevent wastage in areas such as water consumption costs, manpower costs, consumption savings Inputs are inevitable. Planting time management for optimal production in any variety of rice is one of the main and effective factors in production that leads to optimal use of inputs and effective use of existing factors such as weather conditions. . Among the atmospheric and environmental factors affecting growth, the relative importance of temperature is more than other factors. Environmental factors can affect yield by directly affecting the physiological processes of growth and grain formation. For example, temperatures higher or lower than the maximum and minimum critical temperatures can affect grain yield by affecting tilling strength, cluster formation and ripening.
Materials and methods:
Gilan province is one of the northern and coastal provinces of the country with an area of 14711 square kilometers, which has a temperate Caspian climate. Considering that out of the total 238 thousand hectares of paddy lands of the province under cultivation of native and high-yield rice cultivars, about 180 thousand hectares, i.e. about 76% of it is dedicated to cultivation of Hashemi cultivar, we can understand the importance of this cultivar in the agricultural economy of the province. Which emphasizes the need to obtain more information than this figure in the province. For this reason, the cultivar studied in this study was selected Hashemi, which has been transplanted in different planting dates and the purpose of the study was to compare and compare the length of growth period in the mentioned dates in the sample farms. In this study, meteorological information was obtained during the 94-95 crop year, including the average daily values of air temperature in different stations of Guilan Meteorological Department, as well as agricultural information, information on rice phenological stages and physical progress of rice farming operations in Different regions of the province were received from the Jihad Agricultural Organization of the province and its affiliated managements and certain experts in the sample farms.
Results and discussion:
According to the data obtained from monitoring different stages of phenology, in all 8 cities, two Hashemi rice fields with different planting dates were selected and studied and compared. The length of the growth period in terms of days and the amount of GDD received at each phenological stage in these fields were compared with each other. To do this, first, through K-S test the normality of daily average temperature data in all cities was checked and it was found that the data are normal with 95% confidence level. In the next step, the Levine’s Test of variance was performed first, then a comparison was made between early and late sowing fields in terms of GDD intake in different phenological stages. For this purpose, the mean t-test was used. The results showed that only in 3 to 4 leaf stage there was a significant difference between early and late planting fields in which the average degree of growth day received in 3 to 4 leaf stage in early planting fields was 135.4 Units and in late planting farms has been 90/02 units. Also in this study, a comparison was made between early and late planting fields in the western, eastern and central regions of the province in terms of GDD intake at different phenological stages. For this purpose, the mean t-test was used and the results showed that the farms in the center and west of the province had significant differences only in the physiological maturity stage so The farms in the center of the province received 102.825 units in the physiological ripening stage, more GDD than the farms in the west of the province with 59.950 units were needed for this phenological stage. The results showed that the transplanting date in the two selected farms of Rasht city was 541 and 38 July, respectively, and the date of physiological maturity of both farms was 141 days. In other words, a difference in the planting date of 16 days not only did not affect the ripening time but also caused a waste of inputs and human resources. The reason for this is the low temperature in April, when the rice plant will naturally receive less GDD. The highest rate of heat unit reception in most cities (except Astara) was in the tilling stage and the lowest rate of heat unit reception occurred in the physiological maturity stage. It was also found that in most cities, early planting fields in the phenological stages of clustering and hardening of GDD seeds needed more than late planting fields.
In this study, it was found that Hashemi rice in Gilan province, from seedling stage to physiological maturity, needed more GDD in early planting fields and reached maturity in a longer period of time. And has a longer growth period than late planting fields. Hashemi rice in Gilan province has received the highest GDD in the phenological stage of tilling and the lowest amount in the physiological maturity stage. This study showed that Hashemi rice in Gilan province from seedling to physiological maturity will need to receive 1216 to 1352 GDD units. On the other hand, the harvest date can be due to climatic conditions and limitations and Manpower occurs between 2 and 7 days after physiological maturation. It was also found that the eastern regions of the province had both lower GDD and shorter duration during the season than other regions of the province. Therefore, it can be concluded that Hashemi rice in Gilan province from seed to harvest will need approximately 1400 to 1500 GDD units.