State-level crop yield datasets were obtained from CONAB (http://
www.conab.gov.br/conteudos.php?a=1028), which provides official
data on planted area, production and yield back to 1976 for all regions
and states in Brazil. The data are collected through survey agents in
the agricultural sector, including farmers, cooperatives, secretaries of
agriculture, rural extension and financial agents. This work is carried
out monthly, with bimonthly field visits supplemented by contacts via
phone, electronic mail or other means available for updating the data.