Disadvantages of Fertilizers

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Excessive air- and water-borne nitrogen from fertilizers may cause respiratoryailments, cardiac disease, and several cancers, as well as can "inhibit crop growth, increase allergenic pollen production, and potentially affect the dynamics of several vector-borne diseases, including West Nile virus, malaria, and cholera

1.  Crops grow better, but so do weeds. Therefore herbicide sprays are required too.
2.  Better quality plants attract insects so pesticides may be needed.
3. Excess nitrogen from fertilisers gets into water supplies, causing fish to die.
4. Chemicals need to be used safely. In poorer countries in particular, farmers can 
5. damage their health by applying fertilisers, pesticides and herbicides incorrectly.
6.  Artificial fertilisers, applied without organic additions, do not improve soil structure.

The biggest issue facing the use of chemical fertilizers is groundwater contamination. Nitorgen fertilizers break down into nitrates and travel easily through the soil. Because it is water-soluble and can remain in groundwater for decades, the addition of more nitrogen over the years has an accumulative effect.

Groundwater contamination has been linked to gastric cancer, goitre, birth malformations, and hypertension  testicular cancer and stomach cancer

And then there is the highly questionable use of raw sewer sludge as a fertilizer. Yes, you heard me right. In some countries, raw, uncomposted and untreated human waste is applied directly to crops and soil, a practice known as "night soil" since it's typically applied at night. The risk of disease is obvious and high  and this practice should never be confused with "humanure", a long, highly involved process of decomposing human waste into a safe resource.