AbstractThe effects of heavy applications of nitrogen from six different sources on yields and leaf composition of intensively managed coffee, and on acidity of a Los Guineos clay, were determined under typical conditions in the Coffee Region of Puerto Rico. Lowest yields were obtained when nitrogen was applied as sodium nitrate, while applications of ammonium sulfate, ammonium nitrate, potassium nitrate, ammonium nitrate-lime, and urea resulted in the production of similar high yields of coffee. Coffee leaves from plots on which the different sources of nitrogen were used were similar in nitrogen, calcium, potassium, magnesium, and phosphorus contents. However, leaves from the sodium nitrate plots were highest in sodium content and those from the ammonium sulfate plots were highest in manganese content. Soil pH was lowest in the ammonium sulfate, urea, and ammonium nitrate plots, and highest in the sodium nitrate, potassium nitrate, and ammonium nitrate-lime plots. Soil from the sodium nitrate plots was highest in exchangeable sodium. It is evident that sodium nitrate should not be used as a source of nitrogen for coffee. The desirability of using nitrogen sources other than ammonium sulfate on soils with a high content of manganese where this element can cause severe toxicity of coffee is also discussed.
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