Nutrient Leaching from Soil Amended with Manure and Compost from Cattle Fed Diets Containing Wheat Dried Distillers' Grains with Solubles

Livestock manure and compost are commonly used to supply nutrients for crops and improve soil quality. However, excess application may increase the risk of nutrient loss and eutrophication. We investigated the potential leaching losses of nitrogen (N), phosphorus (P), and non-purgeable organic carbon (NPOC) over 105 days in the laboratory. Soils were amended with four treatments: (1) manure (BM) and (2) compost (BC) from cattle fed a typical finishing diet, (3) manure (DDGSM), and (4) compost (DDGSC) from cattle fed diets containing 60 % wheat dried distillers' grains with solubles (DDGS) replacing barley grain. A non-amended control soil was included for comparison. Leachate samples were collected 0, 7, 21, 42, 70, and 105 days after amendment application. Amendment application significantly increased leaching loss of total nitrogen (TN), NO3--N, NH4+-N, total phosphorus (TP), ortho-P (PO43--P), and NPOC from soils by 2.2 to 154.8 times compared with the control. Regardless of whether DDGS was included in cattle diet, cumulative leaching losses of TN, NO3--N, TP, and PO43--P were significantly higher, while NH4+-N and NPOC were lower from compost-amended soil than manure-amended soil. The proportion of cumulative N leaching losses relative to the total N applied was greater with DDGSM and DDGSC than BM and BC, while a greater proportion of total P was leached from DDGSM and DDGSC than BM. Based on the results, more attention should be paid to the potential risk of soil nutrient leaching posed after applying manure and compost, and the higher risk of N and P leaching losses from soil amended with DDGS manure and compost than manure from beef cattle fed typical finishing diets.