EFFECTS OF LIMING, K-FERTILIZATION AND LEACHING ON K-RETENTION, NUTRIENT-UPTAKE AND DRY-MATTER PRODUCTION OF MAIZE GROWN ON A SAMOAN OXIC INCEPTISOL

Effects of coralline lime and leaching on dry matter production and nu trient uptake by maize (Zea mays) were studied in 21 cm deep leaching columns/pots filled with an Oxic Inceptisol (12 kg) from Alafua, Weste rn Samoa. Ground (< 0.25 mm) coralline material containing approximate ly 80% CaCO3 was used as lime. There were 12 treatments, factorially a rranged: 4 liming rates (0, 10.5, 21.0 and 31.5 g pot-1) which were ap plied to the top 5 cm of the pots, and 3 K applications (0, 0.69 1.38 g pot-1) which were applied after the initial leaching period of 10 da ys (3 1 pot-1 day-1) following the lime applications. Leaching continu ed for 15 more days, using 1 1 pot-1 day-1, after K fertilizations. Du ring the initial leaching period, liming intensified K losses. The app lied Ca-ions displaced the exchangeable K which was subsequently leach ed out of the pots. During the second leaching period, liming increase d K retention only when K concentrations in the soil were high (treatm ent receiving 1.38 g K pot-1). These effects of liming and leaching on K retention were not detectable in the nutrient uptake of maize grown for 50 days after the second leaching period. This may have been beca use the leaching losses made up only approximately 2% of the K-turnove r in the pots. A calculated nutrient balance for the pots showed that a large portion of K taken up by maize came out of a pool of nonexchan geable K. The Alafua soil had 0.45 % (11.5 cmol(+)kg-1) total-K, indic ating a relatively large K reserve. Since mineralogical studies failed to detect the presence of any known 2:1 minerals, the K reserve of th e Alafua soil might be located in amorphous material.