Field fertilizer trials were conducted in four of the important agricultural areas of Colombia. These areas were the Sinu and Cauca Valleys, the Savanna of Bogota, and the Mountains. Elevation ranged from about 70 to 10,000 feet above sea level with a correspondingly wide range in temperature, soils, and crops. Greenhouse pot tests with lettuce as the indicator crop and laboratory studies were made on samples of soils from field test sites. Soils from the Savanna of Bogota and the Mountain areas were found to be low in available P as shown by crop response in the field. Yield increases of about 40% were obtained with both potatoes and wheat by application of P fertilizer. There was little crop response to added N fertilizer, except in the Mountain area. With the exception of one soil, K was found to be present in ample quantities for the crops tested in all of the areas. There was a poor correlation between the field response to applied N and P, and the greenhouse and laboratory results under these widely different soil conditions. Mean values for soil pH were inversely related to the elevation of the areas. Values for pH ranged from 6.6 for the sample from the Sinu Valley (elevation 66 feet) to 5.2 for the Mountain area (elevation 7,000 to 10,000 feet). Mean organic matter content of the soil was positively related to the elevation. Mean values for organic C were 2.07 and 9.44% for the Sinu Valley and Mountain areas, respectively.
