Eficiência agrícola da produ？？o de soja, milho e trigo no estado do Rio Grande do Sul entre 1980 e 2008

agricultural efficiency (ea) is used as an indicator of the level of regional agricultural development, reflecting, by mean of the ratio between actual and achievable yields, the crop technology level. based on that, the objective of this study was to evaluate the ea for soybean, corn and wheat crops in the state of rio grande do sul, brazil, between 1980 and 2008, identifying the main factors which conditioned it. ea was obtained by the relationship between the achievable yield (pa) and actual crop yield (pr). pr was obtained from the brazilian institute of geography and statistics (ibge) data base. pa was obtained by estimating the potential yield (ppf) with the fao agroecological zone method, penalized by the water deficit for each crop phase. average eas for corn, soybean and wheat crops were 54, 61 and 43%, respectively. on the contrary of the majority of location, in santa rosa, s？o borja and veranópolis ea values were negative for soybean crop. the main factors that contributed to the increase of ea, in the majority of the locations, were: change on the soil use and fertility; use of agricultural machinery; prices paid for commodities; investments in research and development; climatic risk zoning; and plant breeding.