A farmer would like to know if a new fertilizer increases his crop yield. In an effort to decide this, the farmer recorded the yield for 9 different fields prior to adding fertilizer and after adding the fertilizer. The farmer assumes the crop yields are approximately normal. Does the fertilizer work as advertised?

If the fertilizer did not increase the yield of the crop so it means that the material the farmer used is not a fertilizer. Fertilizers has the ability to increase the yield of crops due to supply of essential nutrients that a plant requires for their growth and development.

There are two reasons if fertilizer did not work.

1) If the soil contains sufficient nutrients and you apply fertilizer so it causes toxicity and crop yield is adversely affected.

2) There are some crops like leguminous crops which make their own fertilizer through nodules. If a farmer apply fertilizer so it has no use.

true, i don't really know what you're asking but from the info you provided im guessing the answer is true.