Dairy farm nutrient management model: 2. Evaluation of different strategies to mitigate phosphorus surplus
To reduce (P) surpluses on dairy farms and thereby the risk of P losses to natural waters we studied different management alternatives by a nutrient balance model described in the companion paper. The strategies evaluated mitigating the P surpluses were: mineral P fertilisation, dietary mineral P supplementation, replacement rate, animal density, production level, feeding intensity, dietary P concentration and nutrient efficiency in crop production. Responses to several interventions (e.g. mineral P fertilisation, purchased feed P, replacement rate) were similar to those observed in Finnish field studies. Reducing or completely giving up the use of purchased mineral P fertilisers was the most efficient measure to reduce P surplus. The slope between the amount of mineral fertilisers and P surplus was 0.98-0.99 (in the field data 1.0). Increased animal density resulted in a greater P surplus, but the slope between P input from purchased feed and surplus was considerably smaller (0.65) than that of P fertilisation. Increasing milk yield with improved genetic potential of the cows would have minimal effects on P surplus per unit of product, but it would increase P surplus per hectare. When the intensity of energy and protein feeding was increased, P surplus rose markedly both per unit of product and hectare. This is (1) due to increased dietary P concentration and (2) due to smaller marginal production responses than those calculated from feeding standards. Reducing dietary P concentration by constraining P excess per kg milk in least-cost ration formulation improved P efficiency in milk production and dairy farming system. However, feed cost increased as low P energy (sugar-beet pulp) and protein (soybean meal) supplements are more expensive than cereal grains or rapeseed feeds. Improving the nutrient use efficiency in crop production had a strong influence in the whole-farm efficiency and P surplus. The modelling results showed that Finnish dairy farms have a great potential to improve P efficiency and reduce P losses to the environment, even by increasing production intensity (milk/ha). It is concluded that the most cost-effective scenario to mitigate P surpluses at a dairy farm would be to reduce or give up the use of mineral P as fertilisers and supplements, and to improve the use of present soil P reserves.
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- Buysse, J. & Van Huylenbroeck, G. & Vanslembrouck, I. & Vanrolleghem, P., 2005. "Simulating the influence of management decisions on the nutrient balance of dairy farms," Agricultural Systems, Elsevier, vol. 86(3), pages 333-348, December.
- Nousiainen, J. & Tuori, M. & Turtola, E. & Huhtanen, P., 2011. "Dairy farm nutrient management model. 1. Model description and validation," Agricultural Systems, Elsevier, vol. 104(5), pages 371-382, June.
- Babcock, Bruce A., 1992. "Effects of Uncertainty on Optimal Nitrogen Applications (The)," Staff General Research Papers 10588, Iowa State University, Department of Economics.
- Modin-Edman, Anna-Karin & Oborn, Ingrid & Sverdrup, Harald, 2007. "FARMFLOW--A dynamic model for phosphorus mass flow, simulating conventional and organic management of a Swedish dairy farm," Agricultural Systems, Elsevier, vol. 94(2), pages 431-444, May.
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