**2.1 Increasing seeding rates with low Fe-EDDHA rates**

It is generally reported that increasing seeding rates will reduce visual chlorosis ratings (early and/or mid-season) and often will increase grain yield when soybean is grown where Fe deficiency is moderate to severe (Uvalle-Bueno and Romero, 1988; Penas et al., 1990; Goos and Johnson, 2001; Lingenfelser et al., 2005; Wiersma, 2007). Increasing seeding density (seeds unit-1 of row), and, presumably, increasing the volume of soil occupied by roots unit-1 of row, can lead to higher yields and higher seed [Fe]s, but may have little influence on early-season VCS (Fig. 1 A, C, E). When averaged across 3 years, 4 replications, 3 cultivars, and 5 rates of Fe-EDDHA, increasing seeding density almost 3-fold reduced visual chlorosis about 12% (Fig. 1 A). On the other hand, increasing Fe-EDDHA rates (in accordance with the severity of IDC) will markedly reduce early season VCSs, but may have little influence on grain yield (Fig. 1 B, D, F). Averaged across 3 years, 4 replications, 3 cultivars, and 5 seeding densities, increasing the Fe-EDDHA rate 4-fold reduced early season visual chlorosis about 70% (Fig. 1 B). Fe acquisition, measured as seed [Fe], appears to be regulated primarily by genotype, yet Fe acquisition by less Fe-efficient cultivars can be increased by increasing SD or reducing the severity of Fe deficiency. It is possible to slightly increase seed [Fe] of both susceptible and resistant cultivars grown under severe chlorosis if high rates (>4.48 kg ha-1) of Fe-EDDHA are used (Table 1; Fig. 1 F). Rates of Fe-EDDHA used in these studies (Fig. 1) were much lower (1.12 to 4.48 kg ha-1) than those evaluated in other studies (2.24 to 11.2 kg ha-1) and may have been responsible for the moderate responses to increasing rates of Fe-EDDHA.
