Tufts OpenCourseware
Authors: Kathleen Merrigan, Ph.D., William Lockeretz, Ph.D.


  • US Geological Survey. Fertilizers – Sustaining Global Food Supplies. 1999. University of Massachusetts Amherst. Fertilizers.

Key Questions

Fertilizers – Sustaining Global Food Supplies

  • Which crops among the major crops of the US have high fertilizer recommendation?
  • Why is fertilizer application more than recommended in most crops – corn, cotton and rice?
  • Why is nitrogen application lower than recommended in soybean?
  • What are the reasons for increasing sulfur deficiency in the soils of the world?
  • How self sufficient is the US pertaining to the major nutrient ( N,P,K,S) requirements?
  • What are the issues that may lead to variations in fertilizer production and use in the US?
  • What are the environmental risks posed by fertilizer manufacture and use?
  • Which nutrient is a major contributor to eutrophication of lakes? What are the options available to manage this phenomenon?


  • What is the distinction between high and low grade fertilizers?
  • What does it mean when the fertilizer grade on the bag reads 10:10:10?
  • What are the roles of N, P and K in crop production?
  • What is nitrogen fixation?
  • What are the problems from over-fertilizing with N?
  • Why does overfertilization with nitrogen result in the crop being more susceptible to pests?
  • What are the major differences between organic and chemical sources of nitrogen fertilizers?
  • What special considerations would a farmer take while using organic nitrogenous fertilizers?
  • Which forms of nitrogenous fertilizers are most commonly and widely used in US agriculture?
  • What are some of the important points to be considered while applying urea on crops?
  • Why should safety precautions be taken while using ammonium nitrate?
  • Would you recommend ammonium sulfate on an acidic soil?
  • Would you recommend ammonium sulfate on sulfur deficient soils?
  • What is the disadvantage of calcium nitrate, despite it being a high quality nitrogenous fertilizer?
  • How is nitrogen mineralization different in blood and seed meals? Does this affect the time of application for crop production?
  • Can sewage sludge application on food crops pose a risk?
  • What is phosphorous fixation? How can this be reduced?
  • Does P pose a risk of leaching?
  • Which other nutrients do superphosphate fertilizers supply?
  • Despite occurring naturally, why is potassium chloride not accepted in organic farming?
  • What precaution would be necessary if one were to use plant materials as a source of potash?