Monitoring the Environmental Impact of the Land Application of Composted Organic Waste While Evaluating Its Agronomic Value on the Calcareous Soils of Northern Guam.

One of the most limiting factors to soil quality in the tropical islands of Micronesia is the low organic matter content and poor fertility status especially for the calcareous soils of northern Guam. Soils in this part of the island are typically shallow, low in organic matter, and nutritionally depleted.   Soil organic matter (SOM) therefore, is the most important soil quality enhancer in Guam and the other islands of Micronesia. Soil organic matter content is enhanced by effective management strategies such as; conservation farming practices, and more effectively by land application of composted organic wastes.  The land application of compost helps with the enhancement of organic matter content which in turn improves the physical and chemical properties of Guam’s poorly structured soil.  In our soil program at the University of Guam, we are evaluating the use of compost as an alternative to synthetic fertilizers.  Our goal is to develop management strategies for using available resources for improving crop production while conserving resources and preserving environmental quality.  In our pilot project compost is produced from wood chips mixed with animal manure, chicken litter, and other organic wastes available at the local farms. For this study mature compost is applied on the field at the rate of; 0, 30, 60 and 90 tons per acre as soil amendment and compared with equivalent amount of nitrogen application in the form of triple 16 fertilizer on the poorly behaved ‘Guam soils series’ of northern Guam.  Following the compost and fertilizer application on adjacent plots, corn was planted and monitored for growth performance and yield evaluation.   However, the environmental impact of land application of composted organic waste on ground water quality is of great concern to the residents of northern Guam.  In order to address this concern, we are also investigating the environmental impact of compost application by using suction cup lysimeters for subsurface soil pore water collection and monitoring. In this paper, the methodology as well as up to date data will be presented to illustrate the effect of land application of composted organic wastes on organic matter content and other soil quality indices.  The paper will also discusses and compares the differences in yield and soil quality indexes observed from compost as well as fertilizer applied plots.