NITROGEN MINERALIZATION POTENTIAL AND NUTRIENT AVAILABILITY FROM FIVE ORGANIC MATERIALS IN AN ATOLL SOIL FROM THE MARSHALL ISLANDS

Abstract

Soil nutrient deficiencies are a major constraint to crop production on the low-lying atoll soils of the Marshall Islands. Despite the critical role organic matter plays in controlling the fertility of these soils, there is little information on the use of organic inputs to improve soil fertility and crop production. In this study, we evaluated the N mineralization potential and nutrient supplying capacity of five organic soil amendments (Vigna marina and Cocos nucifera leaves, chicken manure, fish meal, and copra cake) available in the Marshall Islands. Nitrogen mineralization kinetics were best described by using a modified Gompertz equation with three parameters estimating N mineralization potential (No), mineralization rate (k), and mineralization lag phase (λ). There were significant differences in Chinese cabbage growth in the soil amended with the different organic amendments. Chinese cabbage growth in the Vigna and chicken manure treatments was similar to the chemical control, but the fish meal and copra cake treatments showed significantly less biomass production than the chemical control. The reduced growth in the fish meal treatment was attributed to K deficiency due to the low K supplying capacity of the amendment. The soil amended with coconut leaves showed the lowest biomass production, and the poor growth was attributed to net N immobilization. Optimum corn growth was achieved by adding fresh Vigna leaves at 8.9 T ha -1 (dry weight), and Vigna seems to be a good locally available soil amendment that corrects the multiple nutrient deficiencies found in Marshall Island soils.