Author
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Powell, Joseph |
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Submitted to: Meeting Proceedings
Publication Type: Proceedings Publication Acceptance Date: 8/28/2014 Publication Date: 8/28/2014 Citation: Powell, J.M. 2014. Nitrogen use and trade-offs on dairy farms: an illustration of complexity. Proceedings of Wisconsin Nitrogen Science Summit & Roundtable Series. Presentation No. 8. Interpretive Summary: Technical Abstract: This presentation elaborates the complexity of nitrogen (N) use and N loss from dairy production systems. All biological systems (not just dairy) are limited in N use, major portions of agricultural N inputs are lost to the environment, N loss pathways are diverse, and there are tradeoffs in N use, N conservation and N loss. The biological limit of cows to incorporate their feed N into milk is a fact of life and not very manageable. There are fixed physical and operational features of dairy farms, such as barn and manure storage systems, soils and rainfall that impact nitrogen use efficiency (NUE), and these are somewhat, but not easily managed. Nitrogen applications to avoid risk are manageable practices. Nitrogen use efficiency on dairy farms can be measured at three scales: whole-farm NUE (percent of all farm N inputs that is recovered in N crop and livestock products), feed NUE (percent feed N intake by dairy cows that is transformed into milk N), and manure NUE (percent of land-applied manure N that is recovered in crops). Three examples of tradeoffs in N use and N loss were offered: (1) although reductions in dietary crude protein reduces urea N excretion by dairy cows and N loss as ammonia and nitrous oxide, this practice can also decrease the fertilizer value of manure, (2) although land areas of corn silage may feed more cows than land areas of alfalfa, corn silage requires more N, both to grow the corn and to offset the N that is immobilized (made unavailable to plants) after land application of manure from cows fed corn silage, and (3) although soil tillage reduces ammonia loss from land-applied manure, it can increase nitrate leaching through soil. The maintenance of good stocking rates, feeding the most balanced (CP-energy) rations, collection of manure especially the conservation of urine, and incorporation of N use and N loss tradeoffs into overall N management planning can improve NUE and the environmental impacts of milk production. |
