LW-I-2: Yield fluctuations
2023 Monitoring Report on the German Strategy for Adaptation to Climate Change
2023 Monitoring Report on the German Strategy for Adaptation to Climate Change
Yields fluctuating from year to year can be attributed more directly to changes in weather patterns than to long-term yield trends. Any increase in yield variability increases the production risk for agricultural businesses. Extreme years tend to result in substantial deviations – either positive or negative – from yields achieved in preceding years.
An extended vegetation period, higher temperature totals and higher CO2 concentrations in the atmosphere are apt to stimulate photosynthesis and plant growth. On the other hand – droughts, storms, heavy rain, hailstones and floods can entail increasing risks of yield losses.
Over the past fifty years, advances in plant breeding and technical progress have brought about increases in agricultural yields for important crop species in Germany. Breeding efforts have produced new varieties with improved properties in terms of amounts and stability of yields, quality, resource efficiency, stress tolerance and disease resistance. Likewise, there were improvements in terms of sowing, plant care and harvesting methods as well as fertilising and plant protection. It is true to say, however, that yields are dependent on several other factors besides. In respect of wheat, it was possible to observe stagnation in yields, especially since the turn of the millennium, and in recent years even a slight decline. This development was due to a complexity of causes that will have to be examined more closely. Apart from factors already mentioned, it is possible that cultivation on less fertile soils, so-called marginal sites, may be one of the causes; another factor may be crop rotation at closer intervals. With regard to silage maize, the yields recorded in the time series concerned indicate stronger fluctuations; there is no distinct trend discernible regarding yields. It is important in agriculture to optimise operational management and use of resources. To what extent yield-enhancing measures are taken continues to depend largely on the achievable level of product pricing. The higher the price level, the greater the benefit from the use of yield-enhancing or yield-safeguarding materials such as mineral fertiliser and pesticides. In the past two years, it was above all the high price increases in respect of fertilisers which impacted management operations.
For the time being it is difficult to estimate to what extent climate change influences the absolute yield levels in Germany. Some participants in the debate argue that at least regionally the climate might impose limitations on a further increase in yields. Others argue that the CO2 fertilising effect is making itself felt, and those individuals expect that the agricultural sector will be able to cope with long-term climate trends. In particular regarding the cultivation of annual crops, there are many options available for responding to the changed framework conditions, for instance by choosing appropriate crop species and varieties, by crop rotation and by adapting management planning accordingly. Such adaptive responses have already been in use for decades in agricultural practice, because changing market conditions have always meant that businesses have had to be highly responsive.
It is to be expected that increasing weather- or weather-pattern – fluctuations will occur from year to year, associated with climate change, and these are less easy for agricultural businesses to prepare for. On one hand, weather extremes such as long drought periods, but also heavy rain (for instance during harvest) can lead to unpredictable drops in yield. On the other hand, it is also conceivable that unexpectedly favourable weather scenarios entail surprisingly high yields. Both versions make forward planning difficult and entail production risks, because any calculation will have to be inclusive of the materials to be used and the storage capacities required, based on the yields expected.
Looking at the example of winter wheat – currently the most important cultivated crop in Germany – in respect of the deviations of annual yield from the average yield achieved in the six preceding years, it becomes clear that the yields in this sector – from the turn of the millennium onwards – went through a lot of ups and downs. The trend towards more frequent and more negative impacts on yield outliers has become significant too. The situation is similar in respect of silage maize, but so far it is not possible to see a statistically distinct trend. A possible explanation for the reduction in the yield capacity of winter wheat is above all the shortened phase of grains filling as a result of heat and drought in June. If the harvest month of August turns out to be too wet, this will lead to damage during storage and to pre-harvest sprouting. As far as silage maize is concerned – which as a summer crop is sown and harvested later – other development phases might be vulnerable to weather patterns. In the hot and dry year of 2003, the wheat yield amounted to 65.5 dt / ha which was 14.6 % below the mean yield calculated for the preceding six-year period. Apart from heat and drought, regional outwintering damage owing to black frosts also impacted the yields. In respect of maize, the hot and dry weather pattern in July and August 2003 triggered premature ripening in many locations which enforced early harvesting. In 2010, many locations suffered persistent rain in August, and harvesting conditions remained poor well into September. Both factors entailed adverse effects on maize yields. There is also striking evidence for decline regarding maize yields in 2013. At the end of May flooding occurred throughout Germany, whilst there were also late frosts in some localities. Subsequently, there was a delay in flowering, and there were problems with weed control. In early August, hailstorms and stormy bouts of heavy rain resulted in harvest losses. The extreme drought years of 2018 and 2019 badly affected both winter wheat and silage maize. 2018 was the year with the most significant average drops in yields so far. The difficulties in respect of winter wheat – especially in northern Germany – already began in the autumn of the previous year. Owing to large amounts of rain, the autumn sowing of winter cereals was practically impossible in many cases, and in spring 2018 summer cereals were sown that produced very poor yields. High temperatures and low precipitation levels from April 2018 onwards resulted in an unusually early onset of harvest. Wheat yields for 2018, amounting to 67.7 dt / ha – that is higher than the total of yields for 2003. However, compared to the extraordinary wheat yields of the years of 2013 to 2015, it nevertheless signified a major decline. However, in respect of silage maize, the lowest yield to date was produced in 2018, amounting to 352.9 dt / ha.
It should also be borne in mind that there are, of course, distinct differences between Germany’s regions. In particular in eastern Germany – with its light and sandy soils which react especially fast and strongly to extreme precipitation levels – the interannual yield fluctuations were more pronounced than for instance in the central and western parts of Germany where soils in rather moist and cool upland regions produced more stable yields generally.