Why does beef pollute less than dairy?

There are a number of reasons why dairy farming has greater environmental impacts than beef farming in New Zealand.

1. There are more dairy cattle than beef cattle. In 2013, there were 6.7 million dairy cattle and 3.7 million beef cattle in New Zealand.
2. Dairy cattle are much larger than beef cattle and produce more waste. On average, dairy cattle produce around three times as much total solids, over twice as much nitrogen and phosphorus, and over 40 times the amount of coliform bacteria (pathogens) as beef cattle [1]. This adds up to far more waste and nutrients that could potentially end up in freshwater.
3. In New Zealand, dairy farming is more intensive than beef farming. Dairy farms use more inputs such as fertilisers and brought-in feed than beef farms, and have higher stocking rates. This may be different in other countries where beef cattle are very intensively farmed in barns; in New Zealand in the past few decades we have focused on increasing milk production.
4. Dairy has expanded into areas that are not suited for it, such as Canterbury where more inputs are needed to maximise production, whereas beef farms have been declining in the past few decades.
5. Although beef farms cover a larger national area than dairy farmers, beef farms pollute much less than dairy farms, both per hectare and in total. For example, average leaching rates from dairy land in the Waikato region were calculated at 28 kg of nitrogen per ha, while sheep/beef farms leached 11 kg nitrogen per ha [2]. Leaching rates do vary considerably and actual losses have been measured far higher than these estimations.

Beef farms do have impacts but these are generally worse in other countries with more intensive meat production systems.

References:

[1] Fleming, R. and Ford, M. (2001). Human versus animals – Comparison of waste properties. University of Guelph.

[2] Ledgard, S., Steel, K., Roberts, A.H.C., Journeaux, P.R. (2000). Use of OVERSEER to compare farm systems and countries for nutrient balances, losses and efficiency. In L.D. Currie and P. Loganathan (Eds.) Soil Research – a knowledge industry for land-based exporters (pp. 83-91). Palmerston North, New Zealand: Fertilizer and Lime Research Centre.