@article{Heffernan:137319, recid = {137319}, author = {Heffernan, Peter J.}, title = {Agricultural Letter}, journal = {Agricultural Letter}, address = {1989-08-11}, number = {820-2016-53006}, series = {1766}, pages = {4}, month = {Aug}, year = {1989}, url = {http://ageconsearch.umn.edu/record/137319}, doi = {https://doi.org/10.22004/ag.econ.137319}, }