Skip to main content
ARS Home » Midwest Area » Madison, Wisconsin » U.S. Dairy Forage Research Center » Dairy Forage Research » Research » Publications at this Location » Publication #330450
Title: Estimating nitrogen excretion and deposition in grazing dairy systems

Author
item AARONS, SHARON - Department Of Primary Industries
item GOURLEY, CAMERON J. - Department Of Primary Industries
item Powell, Joseph
item HANNAH, MURRY - Department Of Primary Industries

Submitted to: International Nitrogen Conference
Publication Type: Proceedings
Publication Acceptance Date: 9/9/2016
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Current approaches to improve nutrient management on Australian dairy farms target the application of fertilizer nutrients to pastures. However, increasing animal densities and greater reliance on purchased feeds means that nutrient inputs in the form of feeds and therefore manure have increased. A better understanding of how grazing animals impact nutrient flows, and incorporation of this information into on-farm nutrient management plans can enhance the profitability and environmental impacts of the Australian dairy industry. Quantifying feed nutrient intakes and therefore manure nutrient excretion is difficult, due to challenges in estimating pasture dry matter intake (DMI) by grazing cattle. To quantify N use and fluxes on dairy farms we modified an animal performance model to estimate annual DMI, feed N intake (NI) and manure N excretion (Nex). Using herd management data and Nex simulations, we estimated Nex loading rates to specific locations visited by the lactating herds within the dairy farms. The dairy herds received on average 52% of their metabolizable energy requirements from purchased feed supplements. Calculated annual N flows through the lactating herds were 60% of total N inputs (fertilizer applied to pastures, purchased feed) onto these farms. Average NI (545 g N/cow/day) were well in excess of recommended levels resulting in average manure Nex of 433 g N/cow/day. Depositions of Nex were not uniform, with 30% more Nex returned to paddocks which are typically closest to dairysheds. Lowest Nex depositions occurred in the dairysheds and adjacent yards. However, Nex from dairysheds is collected and typically applied as effluent to paddocks closest to the dairyshed. These N applications can further exacerbate N accumulation and potential N losses from these parts of dairy farms. Quantifying Nex and spatial aspects of Nex depositions by grazing dairy cows could improve overall N management, N use efficiency and decrease N loss from Australian grazing-based dairy farms.