Investigation of the effect of air temperature in Guilan province in determining the appropriate time for rice cultivation

Many parameters affect the length of rice growth period, including air temperature, evapotranspiration, effective rainfall, soil temperature, soil moisture, amount of water available, fertilizer intake, crop management. Among the above factors, the effect of air temperature on the length of rice growth period is more significant, so in this study, using air temperature, the heat requirement (degree - day of growth) required to complete the length of rice growth period was investigated. The degree-day of growth is one of the most important indicators in agricultural management and knowledge of the extent and probability of its occurrence in the region will improve the agricultural calendar.

The purpose of this study was to investigate the effect of changing the planting date on the growth period of Hashemi cultivar rice based on degree-day of growth (GDD) in Guilan province. For this purpose, the average daily temperature data of 13 stations of Astara, Anzali, Talesh, Jirandeh, Deilman, Airport, Rudbar, Rudsar, Keshavarzi, Kiashahr, Lahijan, Masouleh and Manjil were used over an 11-year period (2008-2018). In this research, the degree-day of growth of Hashemi rice cultivar was 1450 units with physiological zero of 11 degrees Celsius for 8 planting dates with 10-day intervals from 10 April to 20 June. Harvest dates were calculated with 25, 50 and 75% probabilities using Pearson type III distribution function and were interpolated for plain areas of Guilan province with the help of GIDS algorithm.

Since it is necessary to consider the length of the rice growing period in low and rainy years (drought and wet years), we decided to examine the zoning at three levels of probability. Let's. It is worth mentioning that in this research, the first day of Farvardin is considered as the first day of Julius. First, harvest dates in cities with meteorological stations were calculated and compared, which showed that in all cultivation dates of Astara, Talesh, Rudsar and Lahijan, respectively, the longest growth period and Rudbar city, respectively. They also have the shortest growth period.In order to study the length of the growth period in other areas of the province that do not have a meteorological station, using the GIDS algorithm and with a spatial resolution of 900 meters (0.01 degrees Celsius) for all plain areas of Gilan province, the length of the growth period was internalized and the results Zoning was presented at three levels of probability. In order to show the error rate of the interpolation method, the root mean square error (RMSE) statistic was used. For example, according to the zoning done at the level of 25% probability, the areas of Shaft, Fooman and Soomehsara have shorter growth periods than other parts of the province. However, it should be borne in mind that the longer the planting date to summer, the shorter the growth period. For example, for the city of Fooman, if the planting date is on the 10th of Farvardin (July 10th), the harvest date will be approximately on the 6th of August (130th of July), ie the growth period is 120 days. Now, if we move the planting date in the same city to 10 June (72nd day of July), the harvest date will be 5 September (160th day of July), ie the length of the growth period is 88 days. This 32-day difference during the growing season can save on input consumption (fertilizer, water, time, planting costs.

Environmental changes affect the growth and development processes of plants and ultimately the production and yield of crops. Given this point, planning to select the appropriate planting date for each crop and reduce the negative effects of these environmental changes, has a significant impact on economic gain and prevent waste of resources. Therefore, zoning of areas based on GDD can be of special importance in carrying out timely and correct agricultural operations as well as better use of agricultural lands.In this study, the results showed that in all cultivation dates, the areas of Fooman, Shaft and Soomehsara had the shortest growth period and the longest growth period was related to Asalem, Talesh and Astara, Kiashahr and Rudbaneh regions. It was also found that the longer the planting date is from April and closer to June, the shorter the growing period will be due to the low temperature in April, when the rice plant will naturally receive less GDD. In all cities of the province, the most appropriate planting date in terms of shorter growth period was related to the dates of 10 and 20 June.