Climatic efficiency (EC) is an index that shows the yield loss caused by water deficiency. The objective of this study was to evaluate the EC of soybean and wheat crops for the state of Rio Grande do Sul, Brazil. The EC was obtained by the ratio between the attainable yield (PA) and potential yield (PPf) of these crops, estimated by crop simulation models. The PA was obtained by estimating the potential yield (PPf), which was determined by the FAO Agroecological Zone method, depreciated by the water deficit in each crop phenological phase for each sowing date, between 1979 and 2008. The results showed that sowing dates influenced the EC for the soybean crop, ranging from 0.31 to 0.61. Based on the results from EC and PA, there is an increase of crop yield when sowings are delayed from 01/10 to 21/12. For the wheat crop, the average EC was greater than 0.81, which allows to conclude that the best sowing dates should be chosen considering the highest PPf. The highest potential yields for the wheat crop were obtained for sowings from mid-June to end July.
water deficiency; agroecological zone method; sowing dates
