EFFECTS OF LONG-TERM NITROGEN, PHOSPHORUS, AND POTASSIUM FERTILIZATION ON CASSAVA YIELD AND PLANT NUTRIENT COMPOSITION IN NORTH VIETNAM

Abstract

The effects of repeated yearly fertilizer applications on cassava (Manihot esculenta Crantz.) yield and plant composition are not well documented in Vietnamese soils. In 1990, a research plot experiment was established on abandoned grassland with 12 treatments to examine effects of different rates of nitrogen (N), phosphorus (P), and potassium (K) on cassava yield and tissue nutrient concentrations in Acrisols in North Vietnam. Cassava yield was measured every year over the period from 1990–1998. In June 1998, composite plant samples (leaf blades) were collected from each plot for nutrient analysis. Generally, cassava showed greater response to N in the latter years of the study due to gradual depletion of N fertility in the absence of N fertilization since cultivation. In plots where P fertilizer was added every year, response to added P fertilizer diminished over time due to accumulation of residue P. Yield responses to added K were large and consistent throughout the nine years of the study. Leaf blade N, K, and P concentrations increased with increasing rates of nutrient addition. The equation: log (yield) = −1.46 + 0.067(leaf N) + 0.225(leaf P) + 0.074(leaf K) -  0.046[leaf magnesium (Mg)] was determined to be effective in predicting cassava yield (R² = 0.93). Based on the results obtained, an N:P₂O₅:K₂O balance of 2:1:2 is recommended for cassava production on these soils.

ACKNOWLEDGMENTS

The financial and technical support ofCentro International de Agricultura Tropical(CIAT) and of the Canadian International Develo±ent Agency (CIDA) are gratefully appreciated.