Forage crop opportunities as a result of climate change
Authors: S Trolove, H Kerckhoffs, R Zyskowski, H Brown, B Searle, A Tait, A Pearson, J Reid
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Executive summary
This report identifies the major opportunities that climate change brings to extend the growing season and increase forage crop yields through radical changes in forage germplasm and management.
The authors used existing crop models and simulated weather data to predict the likely changes in forage crop production in 2040 and 2090. The models grew maize silage over the summer, followed by winter wheat; the biomass was then summed to give total annual biomass production. Three different management practices (sowing dates for maize) were investigated. These studies were carried out for six regions of New Zealand, represented by weather data from Kaikohe (Northland), Hamilton (Waikato), Palmerston North (Manawatu), Masterton (Wairarapa), Lincoln (Canterbury) and Gore (Southland). More detailed modelling was done for Northland: a range of maize hybrids, from short-maturing to novel tropical maize, were tested across three sowing dates, followed by either winter wheat (to simulate a grass or cereal crop) or kale (to simulate a productive forage brassica).
The results suggest that climate change causes maize yields to decline slightly in the northern regions of New Zealand (from Hamilton north), change little in the central regions, and increase as it is grown further south, particularly in Gore. The warmer winters resulting from climate change increased the biomass of winter wheat by 13–19 percent by 2040, and 17–38 percent by 2090.
As a result climate change is predicted to have little effect on total annual biomass yields in Kaikohe (a 2 percent increase by 2090), but should increase yields further south (a 12 percent increase by 2090 in Lincoln). (Note that the Gore results are not quoted since late-maturing maize is not currently grown in Gore.) In general, there was little difference in total annual biomass yields between sowing maize in September or in November (Table 4).
The more detailed modelling in Northland showed that the tropical hybrid was the most productive maize, with the short-maturing hybrid the least productive. Again September sowings produced more maize biomass. A grass (wheat) winter crop was generally more productive than kale, except when medium- or late-maturing maize was sown in September.
The modelling simulations suggested that climate change may lead to increases in biomass production if maize can be sown in early September. However, in practice this may not be feasible due to the high August rainfall in Kaikohe and the heavy soils.
Gross margins on the crops indicated that there is potential to make more money from tropical and late-maturing maize hybrids sown early in the spring, in combination with a winter forage. Assuming that maize silage remains the most profitable forage, then higher income per hectare can be expected in 2040 due to greater production, but this declines in 2090 to similar returns to those in 1990. The greater returns from maize silage will tempt farmers to plant as early as possible, but this must be balanced by the risk of frost and how quickly the soil dries out over winter. Climate change reduces the frost risk, as expected, and reduces winter rainfall in northern and eastern regions, but increases rainfall in western and southern regions.
This analysis suggests that there are opportunities for maize followed by kale in Northland. However, this would require new methods for making silage out of kale to fully take advantage of this option, and adequate pest and disease control methods.
The report also suggested that more research should be done to match the timing of sowing, the maize hybrid, and the choice of winter forage to ensure that the feed quality of both the winter and the summer crop is maximised. The high value of maize silage also indicated that there may be economic benefits from using long-maturing or tropical maize hybrids. Tropical hybrids would require testing under New Zealand growing conditions. There is also the potential to increase biomass by sowing maize in Gore if it can be provided with adequate frost protection.
Further modelling studies are needed to understand the impacts on forage production of more extreme or more conservative emissions scenarios. These will help the government make the policy decisions now that are necessary for a sustainable future.
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