Stochastical Analysis of Phenological Timing Traits of Rainfed Wheat in Golestan Province Using Climate Parameters

Considerng stochasticalnature of precipitation and temperature and high dependence of the eco-phenological timing traits on them, the present study was conducted with the aim of estimating eight eco-phenological traits of rainfed wheat including planting date, emergence date, flowering date, maturity date and length of each stage of growth in Golestan province.

First, studied traits were determined by daily data of maximum and minimum temperature and precipitation of 33 meteorological stations in the 26-year common statistical period (1991-2016). Then, these traits were calculated based on frequency analysis by SMADA software package for 25, 50, 75, 85 and 95 percent occurrence probability level. Planting date was determined based on the first precipitation equal to or more than 25 mm over a period of 10 consecutive days in December. Also, length of each growth stages was determined based on the concept of Growing Degree-Days (GDD). Finally, zoning maps of eco-phenological traits for different occurrence probability level were produced by ArcGIS software. In order to verify estimated eco-phenological traits values, findings from various field scale researches in Golestan province were used. The results showed that estimations and zoning maps wrere done with good precision.

The results showed that the effect of occurrence probability level was significant on all variables, so that with increasing occurrence probability level several important changes were observed: first, a significant postponement of dates of planting, emergence, flowering and maturity; second, a significant increase in the length of planting to emergence; and finally, a significant reduction in the length of the emergence to flowering, flowering to maturity and planting to maturity stages. Zoning maps showed that the suitable planting date for rainfed wheat in 90 percent of Golestan province area for occurrence probability levels of 25, 50 and 75 percent was before 10 December and for 85 and 95 percent occurrence probability levels in 78 and 90 percent of the province area was from 1-20 December and 21 December to  9 January, respectively. Emergence date of rainfed wheat in more than 90 percent of the Golestan province area for the occurrence probability levels of 25 to 95 percent was calculated until 20 December, until 4 January, 21 December to 19 January, 5 January to 3 February and 20 January to 18 February, respectively. Also, flowering date of rainfed wheat was obtained 4 April to 4 May in 95 percent of the province's area for 25 percent occurrence probability level, 5-20 May in 86 percent of the province's area for 50 percent occurrence probability level, 20 April to 20 May in 95 percent of the province's area for 75 percent occurrence probability level, 5-20 May in 75 percent of the province's area for 85 percent occurrence probability level, and 5 May to 4 June in 93 percent of the province's area for 95 percent occurrence probability level. In terms of maturity date, the results showed that this date in more than 90 percent of the Golestan province's area was 21 May to 4 June for 25 percent occurrence probability level, 21 May to 20 June for 50 percent occurrence probability level, 5-20 June for 75 percent occurrence probability level, and 5 June to 5 July for 85 and 95 percent occurrence probability levels.

Based on the average of all weather stations, the increase in occurrence probability level from 25 to 95 percent (risk reduction from 75 to 5 percent) delays the suitable planting date, dates of germination, flowering, and maturity of rainfed wheat by 37, 56, 35 and 28 days, respectively. It also increases the length of planting to germination stage by 19 days while decreases the length of germination to flowering, flowering to maturity stages, and total season by 22, 8 and 10 days, respectively.