Reactive nitrogen losses from dairy production systems

Abstract Text: Reactive nitrogen (N_r) losses from dairy production vary depending on housing type, manure storage system, and manure land application practices. To illustrate on farm N_r losses, we compared three systems:  a dry-lot in ID with 213 lactating and 137 young cattle, a free-stall operation in NY with 1,261 lactating and 925 young cattle, and a free-stall and grazing operation in the Netherlands (De Marke) with 78 lactating and 57 young cattle. The De Marke farm was designed to reduce N_r losses through an efficient feeding program, barn flooring to reduce ammonia (NH₃) losses, enclosed manure storage, injection of manure on cropland and the use of cover crops. Farms were modeled using the Integrated Farm System Model (IFSM) to estimate N_r losses and evaluate effects of mitigation strategies on the ID and NY dairies.  Total estimated Nr losses ranged from 5,727 to 139,455 kg N yr^-1 and comprised 34%, 46% and 50% of imported N from the ID, NY, and De Marke dairies, respectively. The N_r lost per animal equivalent (AE) was 121, 98, and 65 kg N AE^-1 for the ID, NY, and De Marke dairies, respectively.  The N_r losses differed between production systems with 80% of N_r lost as NH₃ (63% from housing) on the ID dairy, while the NY dairy lost 49% of N_r as NH₃ (52% land application of manures), and 46% due to leaching from crop fields. On the De Marke dairy the majority of N_r loss was due to leaching from crop fields and pasture comprising 52% of total N_r lost.  To mitigate N_r losses at the ID dairy, strategies targeted the housing sector by feeding a balanced ration that reduced overall dietary CP, reducing housing emissions by 10 kg AE^-1along with a 1 kg AE^-1reduction from manure storage.  Immediate incorporation of land applied manure decreased N_r losses by 1.7 kg AE^-1. These combined practices led to a 12.5% reduction in total N_r lost. A reduction in dietary CP on the NY dairy coupled with covering the lagoon reduced N_r losses from housing and manure management combined by 5.4 kg AE^-1, while immediate incorporation of land applied manure reduced field losses by 7.8 kg AE^-1. These practices combined reduced total farm N_r loss by 27%. While Nr losses from dairy production can be large, mitigation strategies are available, however they must be targeted to address issues within each production system individually to ensure system-wide reductions.

Keywords: nitrogen, dairy production, environment