Weed management: a need for ecological approaches - Ecological Management of Agricultural Weeds - page 20

Figure 1.5 Economic characteristics ofmaize and soybean production in Iowa,1972-98: (a) yields,(b) non-land
production costs,(c) prices,(d) gross returns,(e) returns above non-land production costs,and (f) herbicide costs as
percentages oftotal non-land production costs.Prices,costs,and returns have been adjusted for inflation using the
Consumer Price Index ofthe US Bureau ofLabor Statistics (base period: 1982-4).Production costs are for
machinery,seeds,pesticides,fertilizers,and labor.Gross returns have been calculated as the product ofstate average
yields (Mg ha 1 ) and prices ($ Mg 1 ).Sources: Duffy & Vontalge (1998 and previous years),and M.D.Duffy,Iowa
State University,personal communication (2000).