Dietary forage impacts on dairy slurry nitrogen availability to corn
Precise feeding of protein and mineral supplement can maintain high levels of milk production and reduce nutrient excretion in dairy manure and losses to the environment. No information is available on the impacts of feeding different silages to dairy cattle (Bos taurus) on manure N cycling in soils. Slurry from dairy cattle fed rations containing alfalfa (Medicago sativa L.; ALF), red clover (Trifolium pratense L.; RCL), low-tannin birdsfoot trefoil (Lotus corniculatus L.; LTBT), or high-tannin birdsfoot trefoil (HTBT) silages were applied to field plots during spring or spring + fall. After spring application, slurry type did not significantly impact soil pH, and only periodically impacted soil NH4–N and NO3–N. Corn (Zea mays L.) N uptake after spring application of ALF slurry was greater than after LBFT slurry application and control plots. Residual ALF slurry plots had 35% greater yield and 49% greater N uptake than control plots, followed by other slurries, which had from 17 to 22% greater yield and 29 to 36% greater N uptake than control plots. Corn yield and N uptake were not impacted by slurry types applied the previous fall. Average residual N recovery by corn in spring slurry-amended plots ranged from 20% (ALF) to 13% (RCL and LTBT). Total-N recovery was highest in ALF plots followed by HTBT and RCL. Low impact of applied slurry types was likely due to several interactive factors, including low rainfall, high indigenous soil N availability, and high response variability associated with indirect estimates of slurry N recovery.