Nutrient balance at chain level: a valuable approach to benchmark nutrient losses of milk production systems

• Published in: Journal of cleaner production 2016, Vol.112 (4), p.2419-2428
• Main Authors: Mu, W., van Middelaar, C.E., Bloemhof, J.M., Oenema, J., de Boer, I.J.M.
• Format: Article
• Language: English
• Subjects: Dairy farm; Environmental performance; Nitrogen; Nutrient use efficiency; Phosphorus
• ISSN: 0959-6526; 1879-1786
• DOI: 10.1016/j.jclepro.2015.09.116

A nutrient balance approach is often used to quantify losses of nutrients, such as nitrogen and phosphorus, that contribute to environmental problems such as eutrophication. A nutrient balance generally is computed at farm level, implying that nutrient losses related to pre-farm processes, such as production of purchased feed, are neglected. Using a nutrient balance at farm level to benchmark livestock systems or individual farms that differ in, for example, amount of purchased concentrates, however, may lead to biased conclusions. To determine whether a nutrient balance that accounts for losses during production of purchased feed (i.e. a chain balance from cradle-to-farm-gate) are more suited to benchmark nutrient losses of milk production systems or individual farms than a nutrient balance at farm level, we analysed 19 Irish grass-based dairy farms and 13 Dutch concentrate-based dairy farms. For each farm, we computed nitrogen and phosphorus losses at farm and chain level (i.e. from cradle-to-farm-gate, including losses from purchased feed production), and expressed these losses per ton fat-and-protein-corrected milk. An independent T-test and Wilcoxon–Mann–Whitney test were used to examine the difference in mean losses at farm and chain level between Irish and Dutch systems. Regression analysis was used to determine if the ranking of the farms changes using a nutrient balance at farm or chain level. Results show that on average, Irish farms had higher nitrogen losses per ton milk than Dutch farms, both at farm (Irish = 20; Dutch = 8 in kg N/ton milk) and chain level (Irish = 22; Dutch = 11 in kg N/ton milk). Phosphorus losses per ton milk, on the other hand, did not differ between Irish and Dutch farms at farm (Irish = 0.3; Dutch = 0.1 in kg P/ton milk) or chain level (Irish = 0.8; Dutch = 1.0 in kg P/ton milk). Regression analysis revealed that the nutrient balance at chain level could be accurately predicted from the nutrient balance at farm level (R2 = 0.992 for N; R2 = 0.910 for P); whereas in case of phosphorus, the slope tended to differ between Irish and Dutch farms (p