Influence of elevated air temperature during grain-filling stage on milling parameters and rice grain wastage under different local climates in Mazandaran province

Rice milling parameters consist of milling recovery, broken grain percent, chalkiness and whiteness due to the effect on waste, price, marketing and final income of production. Reducing in rice grain milling parameters due to climate change and global temperature increase is one of the most important challenges in many of the world's rice planting regions, including our country, and the changes in milling recovery, regardless of agronomic management, depend on the environmental conditions of each region, especially the air temperature on grain filling stage. Therefore, the present study was conducted to investigate the effect of different local climates on milling parameters (MP) of two rice cultivars (cvs. ‘Tarom-Hashemi’ and ‘Shiroudi’) and also to estimate the relationships between MP and average air temperatures (AAT) during the grain filling stage of rice (from anthesis stage (50% of flowers opened) to harvesting time) in Babolsar, Amol and Polesefid regions in Mazandaran province.

Three field experiments were conducted separately based on the randomized complete blocks design with four replications in Babolsar (-21 m sea level, asl), Amol (+24 m asl) and Polesefid (+625 m asl) in the north of Iran on two rice cultivars ‘Tarom-Hashemi’ and ‘Shiroudi’ in 2014. All agronomic managements were done based on local recommendations in each region. Moreover, all studied traits were measured in the grain quality laboratory of Rice Research Institute of Iran, Deputy of Mazandaran (Amol) in three months after harvesting.

The results indicated that the effects of different local climates were statistically significant on percentage of milling recovery, head and broken grain and chalkiness (P < 0.01). All studied traits in Polesefid were better than them in both Amol and Babolsar which can be due to lower temperature during the grain filling stage of rice. In general, milling recovery (1.46 and 1.03 %, respectively), amount of head grain (3.58 and 3.11 mm, respectively) and whiteness (1.25 and 1.42, respectively) increased linearly per unit increase in AAT in both ‘Tarom-Hashemi’ and ‘Shiroudi’, respectively. Inversely, broken grain of rice (2.63 and 2.51%) and chalkiness content (1.65 and 4.24%) increased linearly per unit increase in temperature for ‘Tarom-Hashemi’ and ‘Shiroudi’, respectively. Milling economic benefit also decreased 8000,000 and 12,000,000 Rial ha-1 per unit increase in temperature for ‘Tarom-Hashemi’ and ‘Shiroudi’, respectively.

These results can be used for predicting the amount of rice milling wastage and estimating the effect of temperature on economic benefit under climate conditions of Mazandaran province. Based on our findings in this study, milling parameters variation were related to temperature which can be estimated in both cultivars (‘Tarom-Hashemi’ and ‘Shiroudi’) under different local climates of Mazandaran.