Report: TR 2009/33

Author: Amanda Judge, Stewart Ledgard, Agresearch

Abstract

This project involved the use of the OVERSEER nutrient budget model (version 5.4.3.0) to estimate nutrient budgets and environmental emissions from farms in the Waikato region over time.

Dairy farms:

• Ten years data from 1997/98 to 2007/08 was supplied by DairyNZ from their DairyBase database for Waikato dairy farms for the average milksolids production/ha, the average for the top 25% of milksolids production, and the average for the lower 25% of milksolids production.
• Overall trends on the dairy farms over the time period showed increasing use of nitrogen (N) fertiliser and imported feed, and increasing stocking rates and milksolids produced across all farm categories.
• N leaching per hectare increased over time across all dairy farm categories, as did the concentration of N in drainage water from grazed farm areas.
• Nitrogen surplus increased while N conversion efficiency and farm P surplus decreased over time across all dairy farm categories.
  Greenhouse gas emissions/ha increased by about 20% over the 10 years.  Increased greenhouse gas emissions were correlated with increased N leaching, indicating that management or mitigations to reduce N leaching would also reduce GHG emissions.

Sheep, beef and deer farms:

• Twelve years data from 1995 to 2006 was supplied by Meat and Wool New Zealand from their database for Waikato sheep, beef and deer farms.  This represented the average of Class 3, Class 4 and Class 5 (steep low fertility, easy hill and rolling high intensity) land as determined by slope, stocking intensity and farm system.
• The sheep, beef and deer farms showed no change in overall stocking rate over time across all farm classes.  N fertiliser use increased over time, particularly on the more intensive Class 5 farms. 
• Total greenhouse gas emissions/ha remained relatively constant over time, with a slight decrease in methane and increase in CO2 from sheep, beef and deer farms.
• Nitrogen farm surplus increased slightly over time while N conversion efficiency decreased across all classes of sheep, beef and deer farms.
• N leaching and P runoff showed no changes over time.  An exception was on Class 5 farms where P runoff reduced after 1998 when deer were no longer farmed and corresponds with higher P runoff risk from farm systems with deer.
• Greenhouse gas emissions/ha increased with farm intensity between farm classes 3 to 5 but within each farm class there was no change in emissions over time.

Report comparison:

• Results produced from this report compared with those obtained in a similar report in 2004 showed similar values for N leaching, N concentration in drainage water from grazed farm areas and P runoff for the same assessment years.  Greenhouse gas emissions, particularly on the dairy farms, were higher with the current model which can be partially attributed to changes in the OVERSEER nutrient budget model which have occurred between the version used in 2004 and that used in this report.

Rainfall scenarios: 

• Model scenarios of the effects of increasing rainfall on each farm category for the latest year’s data showed increased atmospheric inputs and outputs, N leaching and P runoff.  The dilution effect of increased drainage with increased rainfall corresponded to a decrease in the N concentration in drainage water from grazed farm areas.
• Factors that are determined largely by stocking rate and production, such as greenhouse gas emissions, showed no change with increasing rainfall.

Nutrient Budgets for Waikato Dairy and Sheep, Beef and Deer Farms 1997/98 – 2006/07 [PDF, 393 KB]