“…The corn yield response to phosphate and potash fertilizer data come from peer-reviewed published work based on field experiments conducted throughout the state of Iowa from 1975 to 2007 and for the most representative types of soils (Mallarino, Webb and Blackmer, 1991;Bordoli, 1996;Barker, 1998;Borges and Mallarino, 2001;Dodd and Mallarino, 2005;Clover, 2008;Mallarino et al, 2009). Each observation in the datasets also contains data on soil type and soil level of phosphate and potash.…”