Submitted to: American Dairy Science Association Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: June 30, 1998
Publication Date: N/A
The objective of this study was to determine if manure C and N mineralization characteristics were altered when cows were fed alfalfa or orchardgrass silage in a TMR. Urine and feces were collected from a companion trial in which lactating cows (2 per treatment) were fed a 30% NDF diet containing alfalfa silage (AS), a 30% NDF diet containing orchardgrass silage or a diet containing orchardgrass (OS) at the same forage to concentrate ratio as AS (35% NDF, ROS). Urine and feces were mixed in the proportions excreted. Rates and extents of N and C mineralization were determined by incubating manure-amended soil at 25oC in an aerobic environment. The production of CO2 and the appearance of NH4+ plus NO3- were monitored over 16 wk. CO2-C production followed first-order kinetics for all treatments. The rate and maximal extent of CO2-C production were not different (P>0.7 and P>0.9, respectively) across treatments (.19 d-1 and 27% of added C, respectively). Nitrification was initiated between 7 and 14 d and all NH4+ was converted to NO3- by 56 d in all treatments. Mineralization of non-urea organic N began between 2 and 7 d in the AS incubations, however, net mineralization was not observed in manure from the OS and AOS treatments until 28 d. Mineralization of N in manure from animals fed the AS diet reached 26% of added organic N by 56 d. Only 15% of the organic N was mineralized at 56 d in the OS and ROS treatments. These data show that although the inorganic manure N is immediately available for plant use, mineralization of the organic N in manure is a slow process and may be affected by dietary forage.