The probability of occurence of days with solar radiation bellow the critica1 value for the development of tomato inside greenhouse in Santa Maria, Rio Grande do Sul State, were calculated during May, June, July and August. It was considered the flue density of solar radiation of 200cal cm-2 dia-1 as the lowest value to tomato growth and 180cal cm-2 dia-1 as the low value referente of solar radiation for crop growth. Daily values of solar radiation were estimated by sunshine duration during the time period from 1912 to 1996. Results showed that the availability of solar radiation in Santa Maria was lower than the required by tomato crop inside plastic greenhouse during Winter, mainly in June and July.
plastic greenhouse; tomato; solar radiation
