LW-I-2: Yield fluctuations

The picture shows a maize field. The leaves of the already tall maize plants are heavily curled due to the drought. Click to enlarge
Yields can vary depending on weather conditions such as heat and drought.
Source: Photograph: © Konstanze Schönthaler / Bosch & Partner GmbH

2019 Monitoring Report on the German Strategy for Adaptation to Climate Change

Table of Contents

 

LW-I-2: Yield fluctuations

Yields fluctuating from year to year can be attributed more directly to changes in weather patterns than long-term yield trends. Any increase in yield variability increases a farmer’s production risk. Extreme years tend to result in substantial alternations between positive and negative deviations from yields of preceding years.

The bar chart shows the deviation in percent of the winter wheat yields from the mean of the 6 previous years for the period 1986 to 2017. Up to 2001, the positive values clearly predominate, in the years thereafter there were strong differences between the years with partly significant positive and negative deviations. There is no trend.
LW-I-2: Yield fluctuations

The bar chart shows the deviation in percent of the winter wheat yields from the mean of the 6 previous years for the period 1986 to 2017. Up to 2001, the positive values clearly predominate, in the years thereafter there were strong differences between the years with partly significant positive and negative deviations. There is no trend.

Source: BMEL (harvest and farm reporting: special harvest and quality assessment)
 

Increased yield fluctuations entail higher production risks

Weather patterns are amongst the most crucial variables which determine agricultural production. An extended vegetation period and increased accumulations of high temperature can increase harvest yields. In addition, higher CO2 concentrations in the atmosphere which are, after all, responsible for causing the greenhouse effect, can stimulate photosynthesis and plant growth. On the other hand, climate change associated with e.g. drought stress or extreme events such as storms, heavy rain, hailstorms and flooding also entails an increasing risk of yield losses.

In 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.

As far as wheat is concerned, agricultural practice has been marked by yield stagnation in the past few years; this phenomenon is due to a complex set of causes which require closer examination. 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. 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.

For the time being it is difficult to estimate to what extent climate change impacts on 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 agriculture can cope with long-term climate change trends because especially in the cultivation of annual crops there are several options of responding to changed circumstances, e.g. by choosing appropriate crop species and varieties, adapting crop rotation and by appropriate planning of management tasks.

It is to be expected that increasing weather fluctuations from year to year will engender greater challenges which confront farmers with greater difficulties to adapt. Weather extremes such as long drought periods can lead to unpredictable drops in yield. In the drought year 2003 for instance, the average wheat yield nationwide was 12 to 13 % below the trend yield expected for that year. Likewise, the past two years saw agriculture confronted with awkward weather conditions resulting in yield drops. In northern Germany rainfall in autumn 2017 was excessively high making autumn sowings of winter cereals impossible in many locations; this led to the sowing of summer cereal crops which produce lower yields. High temperatures and low precipitation levels from April onwards resulted in an unusually early onset of harvest with poor yields. According to findings by the ‘Besondere Ernte- und Qualitätsermittlung’ (special survey of harvest and quality data’ for 2018, compared to the three-year mean, yields for the German cereals harvest were down by 20 %25. In particular in northern and eastern Germany, yields for cereal crops were down by more than 30 %.

Interannual fluctuations in yields will reflect the impacts of climate change more clearly than long-term yield trends in view of the fact that the latter are a reflection of long-term adaptation plans not just in respect of climate change but also regarding market conditions. Fluctuations in yield were calculated by means of the deviation of annual yield from the average yield achieved in the six preceding years. The production risk faced by farmers increases as a function of increasing variability of yields. This is due to the fact that the calculation of factors such as operating resources and materials is based on the expectation of certain yield levels.

Looking at the example of winter wheat – currently the most important cultivated crop in Germany – in respect of the deviation of annual yield from the average yield achieved in the six preceding years, it becomes clear that the yields in this sector went through a lot of ups and downs. However, it is worth pointing out that the figures for this comparatively short time series must be interpreted with caution. These remarkable swings are clearly characterised by extreme years, which makes it currently impossible to refer to a generally valid trend. In the time series covering the period from 1986 to 2017, yield losses caused by the extreme spring drought of 2003 are particularly noticeable.

It should also be borne in mind that there are, of course, distinct differences between Germany’s regions. In particular in eastern Germany – where predominantly light sandy soils are farmed which react especially fast and vigorously to extreme precipitation levels – the interannual yield fluctuations were more pronounced than for instance in the central part of western Germany where soils in rather moist and cool upland regions produced more stable yields.  

25 BMEL – Bundesministerium für Ernährung und Landwirtschaft (Hrsg.) 2018: Ernte 2018 – Mengen und Preise. Berlin, 38 pp.
https://www.bmel.de/SharedDocs/Downloads/DE/_Landwirtschaft/Pflanzenbau/Ernte-Bericht/ernte-2018.html

 

Interfaces

LW-I-3: Hailstorm damage in agriculture