Protein Content in Dairy Cattle Diets Affects Ammonia Losses and Fertilizer Nitrogen Value

Abstract

Abstract Altering feeding strategies for dairy cattle ( Bos taurus ) may reduce manure N excretion and NH 3 emission from the manure. We determined the effect of dietary formulation on NH 3 emission immediately following manure excretion and the availability of manure N for plant growth. Manure (urine and feces) was collected from dairy cattle fed diets containing crude protein levels of 16.4% (T1High), 15.3% (T1Med), and 12.3% (T1Low) in trial 1, and 18.3% (T2High), 16.7% (T2Med), and 15.3% (T2Low) in trial 2. Ammonia emission was measured in the laboratory for up to 48 h. Emissions during the first 24 h following manure excretion were 38 and 23% of the total manure N from Diets T1High and T1Low, and 22, and 15% of the total manure N from Diets T2High and T2Low. Manure NH + 4 concentration and pH were positively related to the dietary crude protein level. Manure from cattle‐fed diets T1Med and T1Low were applied to soil at two rates to determine short‐term N availability for three plantings of corn ( Zea mays L.) grown for 30 d each in the greenhouse. The recovery of manure and fertilizer N in the plants and the soil for the first two plantings was 48, 31, and 103% for the T1Med, T1Low, and inorganic N treatments, respectively. Whole farm N utilization for diets T2High and T2Low were estimated at 18 and 23%, respectively. Feeding diets lower in crude protein increases efficiency of N on the dairy farm, decreases NH 3 emissions following excretion but also decreases the short‐term N availability of the manure.