Thermal and Optical Response of Faba Bean (Vicia faba L.) to Summer Planting Date in Mazandaran Region

Secondary or double cropping not only increases production per unit area but also makes optimal use of other production resources. Faba bean responds to and changes its environment by altering on-site soil fertility, microclimate, and co-habitats of wild flora and fauna. Besides its worldwide use for food and feed, extensive knowledge exists about its ability to symbiotically fix and add nitrogen to the soil, making additional soil nitrogen available and thereby enhancing and sustaining soil productivity. The optimum planting date, optimizes the use of climatic factors such as temperature, humidity, day length, as well as matching flowering time with appropriate temperature. Planting date should be set so that overheating does not harm the plant, especially during the flowering period. A change in planting date may also overshadow the plant's yield by affecting the adaptation of plant growth to environmental conditions, vegetative and reproductive growth (Oplinger et al., 2000). Therefore, knowing the thermal indicators such as the heat accumulation unit, which in most sources is referred to as the degree of maturity days. And all its other mathematical derivations are the same as hlio-thermal unit (HTU), growing degree days (GDD), pheno-thermal index (PTI), crop heat unit (CHU), heat use efficiency (HUE), relative temperature disparity (RTD), It can provide basic principles for determining the phenological stages and the optimum planting date (Sreenivas et al., 2010).

In order to investigate the effect of off-season sowing date (summer) on the accumulation of thermal units, yield and yield components in faba bean var. Luzde otono, an experiment was carried out as split plot based on randomized complete blocks design with three replications during 2017-2018 for two years at Agricultural Research Station Gharakhil (gaem shahr). Experimental treatments were sowing date in four levels of June 10, 30 and July 20, and August 10, main plot and row spacing in three levels of 45, 60 and 75 cm as sub plots. During vegetative and reproductive phases, weeds were controlled and data were recorded on days to flowering, days to maturity, plant height, harvest index, number pods per plant, number of seeds per pod, 100-seed weight, and Green pod yield. Also in maturity, after removing the effect marginal, yield and yield components were calculated. Data were analyzed using the SAS. Ver. 9.1 and figures were drawn by EXCEL and means compared by using DMRT at the 5% probability level.

The analysis of variance showed that the effect of year and planting date and their interactions on number of pods per plant, pod length, plant height and green pod yield were significant (P≤0.01). The unit of heliothermal was greater in 2018 (from 0.47 to 0.88) compared to 2017 (from 0.45 to 0.86), this was due to the increase in average air temperature and the number of sunshine hours. The highest heat use efficiency (HUE) was obtained related to the third sowing date (July 20) in 2018. Also, among the studied indicators, the heat use efficiency (HUE) and the efficiency of consumption of sunny hours (RUE) as well as estimated thermal requirement of faba bean var. Luzde otono in different sowing dates and at different stages of development and in this direction, due to having a constant and logical trend, they have a relative superiority over other indicators such as GDD and PTI.

The results of mean comparisons showed that the highest green pods yield Gained var. Luzde otono in the third sowing date (July 20) with 10422 (kg ha-1) and row spacing 60 cm with 10723 (kg ha-1). Based on the results of this research, To escaped from heat and thermal stress during the reproductive stage of Faba bean in mid-summer and also poding did not coincide with a drop in temperature at the beginning of autumn to achieve the highest yield Faba bean var. Luzde otono should be planted in August.