Abstract Nine field fertilizer experiments involving six major crops were conducted over an 18‐month period in the Cauca Valley of Colombia. The area of moderate fertility selected for study was a farm located on a slightly sloping outwash adjacent to the Andes mountains. In addition to different crops, other variables under investigation included kind and rate of application of fertilizers, plant population, and irrigation. With two similar experiments on corn conducted at the same time on different soil areas, marked yield response to phosphorus fertilizer was obtained at one location, whereas at the second, neither nitrogen nor phosphorus were beneficial. A third experiment dealing with fertilizer, irrigation, and plant population showed that supplemental water and adjustment of stand were more important than fertilizer requirements in determining corn yields. Yields of field beans in one trial were significantly increased by use of nitrogen fertilizer, but only small benefits were obtained from phosphorus. For soybeans, direct application of fertilizer was only of moderate value in improving yields of grain. With sugar cane, one experiment indicated both phosphorus and potassium were needed for high cane production. Nitrogen fertilizer applied to newly planted Pangolagrass was highly effective in increasing forage yield, while response to phosphorus was negligible.