SITE FACTORS, FOLIAR NUTRIENT LEVELS AND GROWTH OF CORDIA-ALLIODORA PLANTATIONS IN THE HUMID LOWLANDS OF NORTHERN COSTA-RICA

Within the perhumid, Atlantic lowlands of northern Costa Pica, Cordia alliodora plantations were studied in order to explain the observed pa ttern of growth irregularities. The soils, that were partly used as pa stures over long periods, could be classified roughly into two units: (i) red, deeply weathered, slightly acidic soils from Mg-enriched pare nt material and (ii) brown, strongly acidic soils with high saturation of exchangeable Al (up to 80%). Leaf analysis revealed that Cordia is a highly demanding species in respect to macronutrients. Poorly growi ng trees in slope position suffered from an insufficient supply of N a nd P. K/Mg ratios of chlorotic leaves are very low. Soil analysis show ed that nutrient deficiencies were related to (i) insufficient soil nu trient reserves of the poor, tropical soils or (ii) to an inhibition o f nutrient uptake by soil physical or chemical factors. All sites are characterized by very low K reserves and losses of nutrients that are organically bound (N, P) caused by erosion. In the Mg-rich red soils, low amounts of K lead to K/Mg imbalances. Soil compaction caused by ca ttle grazing occurs on both soil units. It negatively influences the r oot development of Cordia, and hence nutrient uptake. In the brown soi ls, high amounts of exchangeable Al hinder a sufficient supply of nutr ients (e.g. P) to the assimilation organs.