تاثير عوامل جوي بر بقاي گل و قوزه پنبه در گرگان

Effect of weather conditions on cotton flower and boll retention in Gorgan

Environmental conditions determine productivity of cotton at a given location. An experiment was conducted at Hashem-Abad Cotton Research Station, Gorgan during 2000 under irrigation condition. The objective of the study was to determine the effect of weather conditions on cotton flower and boll retention. To create different weather conditions during flowering and boiling period, different sowing dates were used. Experimental design was a split plot consisting 4 sowing date (24 April, 9 and 25 May and 9 June) as main factor and 3 cotton cultivars (Sahel, Siokra324 and Deltapine) as sub-factor. The percentage of flower and boll shedding linearly increased with delay in sowing date in all the cultivars. An inverse linear relationship was observed between flower and boll shedding and yield for all cultivars. Cultivars showed different slope for the relationship and Siokra324 showed the lowest yield reduction as a function of the shedding. Shedding percentage in Sahel was twice greater than the other cultivars. Significant, positive correlations were found between shedding and mean air temperature and the number of hot days (maximum temperature greater than 30-35°C), but negative, significant correlations were observed for wind speed and relative humidity. Thus, it was concluded that the most important factor is temperature and the effect of other factors (solar radiation, wind speed and relative humidity) is indirect via temperature. The evaluation of the probability of occurrence of hot days showed a high probability of these days during July and especially August. Therefore, it can be recommended that the cotton crops in Gorgan should be sown at first opportunity in spring during April, in order to avoid from high temperature at flowering and bolling stages during August.