Several fertilizer trials with potatoes were conducted for 2 to 3 years (1942 ta 1944) in Trumiw-Osorno fine sandy loam at the Centinela Plant Breeding Station, Puerto Octay, Chile. One trial consisted of applications of N, P, K and Ca singly and in aH possible combinations while another dealt with low and high applications of N, P and K. The object of a thíxd experiment was to compare the effect of a mineral fertilizer with white guano, an organic fertilizer long used by potato growers in southern Chile.
Concerning the results of t.he first test, of the 4 elements alone the greatest and most significant increase in yield of potatoes was obtained with phospbate although a combination of N, P and K gave the highest yield each of the 3 years. Two-years' results on the rate of application were not conclusive but in sorne cases high phosphate and high potassium were more effective than low applications. The results of the third experimeilt indicate that under the conditions of the trial white guano alone was not superior to a mineral fertilizer in increasing the yield of potatoes.