An experiment was conducted for two years at Pale Seco (Guarico Slate, Vene
zuela) on loamy and acid (pH 4.5) soils,vith high potential for soybean pro
duction and low to medium levels of available P, K and Ca. The main objecti
ve was to obtain maximum soybean (FP-3 variety) yields by using increasing
rates of P (0-70 kg/ha) and K (0-135 kg/ha) fertilizers, and to study the e
ffect of these nutrients on the mineral nutrition of the plant. The experim
ental design used randomized blocks and the final plant density was equival
ent to 400,000 plants/ha, with 3 replications. Seeds were inoculated with B
radyrhizobium japonicum, and N (30 kg/ha), Ca (300 kg/ha) and Mg (40 kg/ha)
were applied. A combined year yield analysis showed a linear response to P
and K fertilizers and therefore maximum yields were not obtained. However,
higher yields were produced in the first year, with better rainfall distri
bution, and lower yields, due to excess moisture, occurred in the second ye
ar. The combination of 70 kg P/ha and 108 kg K/ha produced the highest soyb
ean grain yields at 12% moisture, of 2938 kg/ha for the first year and 2713
kg/ha for the second year. In 1997, where P was not applied the leaf P con
centration was at the deficiency level, and the highest P concentration,vas
reached with the rate of 60 kgP/ha. The 18 kgK/ha treatment produced K lea
f concentration within the sufficiency range.