Managing Global Resources for a Secure Future

With the development of the Soil Health Institute in 2013 and its endorsement of 19 Tier 1 soil health indicators in 2017, it is clear that measuring soil health has become a priority. The long-term manure plots, Est.1973, in Lethbridge, Alberta, Canada provide a unique opportunity to assess soil health of both irrigated and non-irrigated agroecosystems subjected to annual manure applications. We used the soil quality indicators from the Cornell Soil Health Assessment to determine how long-term manure applications alter soil properties. In 2016, soil (0-15 cm depth) samples were collected from plots that received 43 annual beef cattle feedlot manure applications applied each autumn at three rates to irrigated (60, 120, 180 Mg wet mass ha^-1) and non-irrigated (30, 60, 90 Mg wet mass ha^-1) agroecosystems. Additionally, soils that had manure applications discontinued in 1987 and 2003 for each rate (after 14 and 30 annual manure applications) and non-amended control soils were also included. Overall, the non-amended, and discontinued and continued manure applications led to a large range of soil organic C concentrations (16–112 g C kg^-1 dry soil). The soil organic C levels had moderate to strong positive correlations with soil protein index, permanganate-oxidizable C, cation exchange capacity, electrical conductivity, ammonium, nitrate, available phosphorus, potassium, sulfate, calcium, magnesium, zinc, manganese and sodium. Soil organic C concentrations were strongly inversely correlated with the pH of this calcareous soil. In these high manure input plots, the soil organic C represents a ‘keystone’ soil health indicator. However, with repeated high application rates of beef cattle manure the increased organic C levels are associated with increased soil salinity, which has limited crop yields. We conclude that finding the optimal range of soil organic C and the associated soil properties to maximize yield will be an important step for assessing soil health after long-term manure applications.