Titanium (Ti) concentration in forages is considered by agronomists to be the gold standard in determining soil contamination of herbaceous materials. However, Ti is not measured in routine nutrient analysis of feed ingredients. Soil contamination of forages reduces the concentration of all nutrients, and soil Fe can decrease the absorption and utilization of dietary copper and perhaps other minerals. The objectives of this study were to determine the relationship between Fe and ash concentrations and to estimate soil contamination from available analytes in commonly used forages in US dairy operations. Data from Cumberland Valley Analytical Services covering the period from 2009 to 2014 for corn silage, legume hay, mixed mostly legume (MML) silage, and mixed mostly grass (MMG) silage were used. Soil contamination was estimated using 2 independent measures, residual ash and Fe enrichment. Residual ash (RA) was calculated according to Cary et al. (1986). Fe enrichment was calculated using the measured forage Fe concentrations and soil Fe concentrations obtained from a US Geological Survey database for the matching location. Linear regression analysis was used to evaluate relationships between total ash, RA, and forage Fe concentrations. As expected, RA was highly correlated with total ash with R² > 0.90 (P < 0.001). Fe was also highly correlated with RA and total ash with R² ranging from 0.47 to 0.63 (P < 0.001). The relationships between Fe and ash concentrations is good across forages, and 1% or greater soil contamination occurs in a significant portion of forages (Table). Level of soil contamination was associated with geographic location. In particular, corn silages grown in the western US had higher (P < 0.001) levels of total ash, RA, and Fe than corn silages from the eastern and midwestern US Table 1. Level of soil contamination (% DM), percentage of samples (Prop), total ash (% DM), and Fe concentrations (mg/kg) of commonly used dairy forages, given as mean ± SD

Soil contamination		Corn silage	Legume hay	MML silage	MMG silage
<1%	Prop	63.5	18.3	8.3	19.3
	Total Ash	3.28 ± 0.47	9.20 ± 1.24	9.21 ± 1.19	6.08 ± 1.56
	Fe	133 ± 83	212 ± 128	265 ± 151	219 ± 170
1 to 4%	Prop	36.0	71.9	78.1	57.6
	Total Ash	5.39 ± 0.94	10.68 ± 1.25	10.55 ± 1.24	8.41 ± 1.77
	Fe	234 ± 139	353 ± 238	423 ± 261	355 ± 252
>4%	Prop	0.5	9.8	13.6	23.1
	Total Ash	8.02 ± 0.60	13.35 ± 1.35	13.51 ± 1.56	12.07 ± 2.03
	Fe	555 ± 313	872 ± 553	1155 ± 576	850 ± 605