Video clip – How commercial growers increase crop yield

This video clip from the BBC TV series Botany: A Blooming History looks at how commercial growers manipulate the limiting factors of photosynthesis to increase crop yield.

With knowledge of limiting factors, it is possible to control the growing conditions for crop plants. This enables faster growing of plants and the increase of their quality and yield. In Holland, massive greenhouses are used to grow peppers in constant light conditions, enabling farmers to reduce the growing season by 4 weeks. Carbon dioxide levels on earth have in the past been much higher. Plants evolved the capacity to use higher levels of carbon dioxide, but under modern conditions the rate of their photosynthesis is limited. Waste carbon dioxide can be directed into greenhouses growing tomatoes. This extra carbon dioxide enables the tomatoes to photosynthesise faster. Increased sugar production improves flavour and increases yield.

A lesson ‘starter’ when discussing limiting factors. Students can do practical work looking at the effect of changing light intensity or carbon dioxide concentration on the rate of photosynthesis. Higher level students can develop the ideas discussed and look at the explanations for the effects seen. The light dependant reactions can be discussed as the point at which light energy is utilised. The features of the enzyme Rubisco can be discussed in an evolutionary context when discussing carbon dioxide utilisation. The impact of commercial plant cultivation on the environment can also be discussed. The balance between improving yield and the use of fossil fuels to generate light could be discussed in terms of costs and benefits. The re-cycling of materials from power stations can be used to illustrate the benefits of carbon neutral technology and innovation.