Julie told her teacher, that she thought additional light would be the best way to increase the yield of crops because it gave the largest increase in yield. Explain why Julie may not be correct.

-Cost-effectiveness matters

Extra light increases yield by 20% for £200 this is 0.1% yield per £

CO₂ increases yield by 15% for £100 this is 0.15% yield per £

Heating increases yield by 10% for £300 this is 0.033% yield per £

CO₂ gives the most yield increase for the least money, so it is more cost-effective.

Limiting factors

Adding light is only effective if light is the limiting factor.

If light is already sufficient, extra light will not increase photosynthesis much.

CO₂ or another limiting factor might actually limit the rate of photosynthesis, so adding them gives better results per cost.

Economic reasoning

Spending £200 on extra light might increase yield only slightly if light isn’t the limiting factor.

Spending £100 on CO₂ gives a large increase for less money, so profit is higher.