Irrigation needs for maize, soybeans and drybeans during crop growing season in southern Brazil

摘要

The objective of this work was to evaluate the irrigation necessity, total number of irrigation and the average irrigation depth applications for maize, drybeans and soybeans in the Planaho region of the Rio Grande do Sul State -Brazil. The climateof this region is characterized as humid subtropical with an average annual precipitation of 1. 730 mm and 430 mm during the crop growing season. Irrigation needs were determined based on crop evapotranspiration estimated from Penman-Monteith equation.A value of 25 mm of cumulative crop evapotranspiration was used as irrigation trigger. Irrigations were applied by a central pivot irrigation system. Crops used in this study were single maize, soybeans and drybeans and double cropping (maize followed bydrybeans in the same growing season). Irrigation needs were determined for the last 10 consecutive years (1990-1999) considering four different sowing dates for each crop. Results indicated that although this region has a high annual precipitation, irrigation applications were necessary for all tested crops in every single year and sowing dates. The minimum and maximum number of irrigation applications were 12 and 57.3 and 32 and 22 and 76 for maize, drybeans and soybeans, respectively. The lower number of irrigation applications were only observed in years of above average cumulative perception. The average irrigation depth applications were 222, 138, 94 and 165 mm for soybeans, maize, drybeans and maize followed by drybeans, respectively. These results clearly indicate that irrigation is necessary in Southern Brazil to maximize grain yield.