Important Note

Tufts ended funding for its Open Courseware initiative in 2014. We are now planning to retire this site on June 30, 2018. Content will be available for Tufts contributors after that date. If you have any questions about this please write to

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?