Effects of dietary protein concentration on ammonia volatilization, nitrate leaching, and plant nitrogen uptake from dairy manure applied to lysimeters

This lysimeter experiment was designed to investigate the effects of dietary crude protein (CP) concentration on nitrate-N (NO₃-N) and ammonia (NH₃) losses from dairy manure applied to soil and manure N used for plant growth. Lactating dairy cows were fed diets with 16.7% CP (HighCP) or 14.8% CP (LowCP) content. Feces and urine were labeled with ¹⁵N by ruminal pulse-doses of ¹⁵NH₄Cl. Unlabeled and ¹⁵N-labeled feces and urine were used to produce manure for a study with 21 lysimeters in a greenhouse. Manure application rate was 277 kg N ha^-1. Ammonia emissions were measured at 3, 8, 23, 28, 54, and 100 h after manure application. Manure was incorporated into the soil, and a leaching event was simulated. Spring barley was planted (387 plants per m²) 7 d after the leaching event and harvested at senescence. Ammonia emission rates and the contribution of urinary N to NO₃-N were on average about 100% greater for HighCP vs. LowCP manures. With both LowCP and HighCP manures, a greater proportion of urinary vs. fecal N was recovered in leachate NO₃-N. There was no difference in wholecrop barley N yields between LowCP and HighCP manures, but barley kernel N yield tended to be greater (p = 0.09) for lysimeters treated with HighCP manures. Using a unique labeling approach, this lysimeter experiment demonstrated that when applied at equal soil N application rates, manure from cows fed the HighCP diet resulted in markedly greater NH₃ emissions and urinary N losses with leachate NO₃-N than manure from cows fed the LowCP diet.