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Long-term nitrogen, phosphorus and potassium fertilization of cassava influences soil chemical properties in North Vietnam

Nguyen, H., J.J. Schoenau, K. Van Rees, D. Nguyen and P. Qian. 2001. Canadian Journal of Soil Science 81: 481-488


The long-term effects of yearly fertilizer applications on soil chemical properties and nutrient availability are not well documented for cassava (Manihot esculenta) production in Vietnam. In 1990, research plots were established (randomized complete block design) with 12 treatments to test effects of different rates of N, P and K on soil properties in Acrisols (FAO-UNESCO Soil Classification) at Thai Nguyen University, North Vietnam. In June 1988, composite soil samples (0- to 10-cm and 10- to 20-cm depth) were collected from each plot. Nine years of N application significantly reduced the labile pools of soil inorganic P, total soil P and soil extractable K and Mg. Total soil N was only slightly increased in the 10- to 30-cm depth. Long-term applications of P significantly increased soil inorganic P fractions, but reduced concentrations and supply rates of nitrate and K. Moreover, 9 yr of K application significantly increased soil organic C (two depths), soil total N (10-30 cm) and soil extractable K in the 0- to 10-cm depth. Generally, the results show that long-term applications of mineral fertilizers in a ratio of N:P2O5:K2O of 2:1:2 (at the rates of 80 N:40 P2O5:80 K2O or 160 N:80 P2O5:160 K20) are effective in maintaining the total content and availability of applied nutrients, but when applied alone are associated with decreases in other nutrients.

Key Words

nitrogen, phosphorus, potassium fertilizers, cassava, ion-exchange resin, soil properties.