This project examined the potential for dairy production whilst farmers operate within the nitrogen-cap for individual farm losses to water that applies within the Manawatū Wanganui Region. Since 2014, various catchments within the Region have been required to obtain their intensive landuse consents in different years. The Upper Manawatu River catchment with over 126 farms is one of the last of these and it provided the focus for this study.
In the study, a nitrogen cap from Table 14.2 of the One Plan was applied to five representative farms selected from dairy farms in the catchment, and the results were used to estimate the possible consequences across all the rest of the farms in the catchment. Two versions of Table 14.2 were considered; the original version in the One Plan based on Overseer® version 5.2.6 (2007) and a second updated version using Overseer® 6.2.3 (2018). Overseer® 6.2.3 was used for the farm system modelling and nutrient budgeting. To fit within their respective nitrogen caps, the representative farms required farm system as well as operational changes to be made including changes in stocking rates. A spreadsheet analysis of the five farms provided the financial results.
It was estimated that if all the dairy farms in the catchment were required to operate within the current nitrogen cap described in Table 14.2 of the One Plan, nitrogen losses from farms would drop by 300 tonnes (60%) and milk production by over 5,000 tonnes (40%) over 20 years. However, over 65% of them would no longer be viable as dairy operations. If Table 14.2 was updated to the latest version of Overseer® then nitrogen losses would drop by over 200 tonnes (40%) and milk production by over 700 tonnes over 20 years (5%). With a revised Table 14.2, the majority of farms could meet the cap and continue to remain viable.