Low temperature is the main climatic risk in Hungarian rice production. There are two forms of cold stress, one of which can cause yield loss due to panicle sterility and the other appears due to elongation of the vegetation period. Optimization of sowing date is a key factor to minimize cold stress.

Our research is based on thermal time phenological models and daily temperature data (1976–2007) of Szarvas. Dates of emergence, flowering and maturity were calculated starting from different sowing dates (5-day steps from the 1st of April until 30th of May) for each year. This allowed us to determine the risk of unfavorably long emergence time and unfavorably late maturity date. Additionally, the flowering period was evaluated regarding the sterile-type cold stress.

According to our results the earliest sowing date recommended is generally 20th of April. Sowing can be done maximum one week earlier if soil temperature is favorable and a persisting warm weather period is forecast. However, only late maturity varieties can profit form early sowing. For early maturity varieties it is advantageous to shift sowing date towards May. The latest advised sowing dates are between the 15th and 20th of May for the early flowering type cultivars and between the 1st and 10th of May for the late flowering type cultivars, according to the maturity type (intensity of water loss at maturity).

Keywords: rice, thermal time model, phenological development, sowing date, climatic risk