SOIL CONDITIONS AND EFFECT OF FERTILIZATION ON THE EMISSION OF GREENHOUSE GASES IN AN ANDEAN COFFEE GRADIENT

Coffee (Coffea arabica and C. canephora) is an important agricultural export product in Ecuador, but yields reported at most coffee farms are low. The main reasons for this are a lack of understanding of soil nutritional status and fertilization management, which implies fertilizer misuse and results in gas emissions into the environment. In this study, the soil nutritional status of coffee plantations was evaluated along an altitudinal gradient of the Ecuadorian Andes as an indicator of soil fertilization plans. A total of 471 farmlands were selected and their pH, soil organic matter, and main macronutrients were determined. The impact of soil fertilization on nitrous oxide emissions was evaluated; for this purpose, an experimental coffee farm was chosen where different doses of mineral and organic soil fertilization were tested, and N2O emissions were determined. The results showed a negative correlation between soil organic matter, pH, and nitrate concentration with altitude. In all altitudinal strata, the nitrate concentration was higher than that of ammonium. In addition, a strong correlation was observed between soil organic matter and soil nitrate concentration. The amount of potassium decreased as altitude increased, whereas medium and high concentrations of available phosphorus were observed in all altitudinal ranges. However, significant statistical differences were found when comparing low mineral fertilization doses to organic fertilization. The N2O analyses showed that coffee plantations fertilized with mineral fertilizers emit from 300 to 1142 mg N2O m-2 into the environment. High mineral fertilization resulted in the highest N2O emissions, with statistically significant differences when compared to low mineral doses and organic fertilization. Therefore, it was concluded that changes in soil nutritional status were observed along the Andean gradient of coffee plantations in southern Ecuador, and that high doses of mineral fertilizer can have a significant impact on N2O emissions.