In moderate climate change scenarios, forage yields in the Waikato have potential to increase, unless there are more damaging extreme weather events and higher pest and disease pressures, according to a study by Plant and Food.

Change in crop varieties and sowing dates can minimise negative impacts of warmer temperatures on yield. However, farmers must continue to improve their farm management practices (irrigation, fertiliser and pest management) to exploit increased yield potentials.

Under severe climate change scenarios, long-term investment in infrastructure (for example, irrigation), and research (for example, crop varieties with new traits), will be necessary to ensure resilience.

The study modelled the potential impact of climate change on a Waikato cropping farm for the period from 2030 to 2049, using NIWA climate change scenarios for 'low” and 'high” carbon emissions during a 20-year period.

The study found the expected average monthly temperature increases ranged from 0.9 degrees Celsius (low carbon emissions) to 1.2 degrees Celsius (high carbon emissions). Average rainfall changed from -1.4 per cent in summer (low) to +20 per cent also in summer (high). The intensity and frequency of rainfall is unknown.

The impacts of climate change for the period 2030-2049 are forecast to result in maize silage yields declining on average by 10 per cent, with a range of -23 to 0 per cent. Warmer temperatures shortened the crop cycle, reducing the opportunity for light interception and photosynthesis. Meanwhile, C4 crops, like maize, do not benefit from the higher atmospheric CO2 levels.

Winter planted green-feed cereal yields increased by 12 to 33 per cent, depending on the climate scenario. These increases were attributable to longer growth periods from the opportunity of earlier planting after the summer maize crop was harvested.

Changes in potato yields ranged from -20 to 16 per cent, with an average decline of three per cent. The yield decrease was due to shortened cycle lengths caused by warmer temperatures, particularly under dry land conditions.

There will be opportunities to adapt to climate change, including to diversify crop rotations, the study says. For example, in dairy supply systems:
• Maize can be sown earlier, and longer maturity hybrids could be used.
• Sowing dates will change; winter forage crops can be sown earlier.
• Adapt storage and processing infrastructure for potato crops.
• Consider use of irrigation to reduce inter- annual yield variability.

Under more severe climate change, selection and breeding of varieties adapted to warmer and drier climates; regional investment improving and expanding irrigation infrastructure and increasing the farming business's financial resilience by reducing debt and diversifying activities will be important.

What is unknown is:
• The way the amount and distribution of rainfall happens will change in the future.
• The impact of elevated CO2 levels on photosyn thesis under field conditions.
• The impact of climate change on the yield damage caused by insects, weeds and pathogens.
• The size of yield losses caused by extreme events such as floods, storms and heat waves.

In the modelling exercise: Low is the B1 emissions scenario, and High is the A2 emissions scenario from the Intergovernmental Panel on Climate Change (www.ipcc.ch), downscaled by the Regional NIWA1 climate model.

The report is published on the Foundation for Arable Research website: www.far.org.nz