Evaluating the Soil Carbon Dynamics Under Cropping Rotations and Conservation Tillage Management On Severely Eroded Soils of Southern Guam.

Severely eroded lands of southern Guam are referred to as badlands.  These are actively eroding areas of very deep, well–drained saprolite derived from tuff and tuff breccia.  These badlands are exposed to overland flow, wind and rain causing sever erosion as the result of rapid runoff from the pitted, sloping sites that are void of vegetation.  The challenge facing soil and agricultural scientists is to develop conservation and restoration strategies that address crop production needs within a framework of increasing environmental and financial constraints.  Toward this end, we will emphasize crop residue management and green manure as means of restoration and conservation of badly eroded soils of southern Guam.  In this investigation, an integrated approach is designed to evaluate the effect of crop rotation with leguminous plants as well as conservation tillage practices not only for soil conservation but also for evaluating the soil carbon sequestration in these severely eroded soils of southern Guam.  An annual legume cover crop (sunnhemp) is planted in rotation to corn as green manure to provide a baseline nitrogen source and increase the organic matter content of these eroded soils.  The objectives of this project are to:  1) Evaluate cropping rotation and tillage management practices on the dynamics of soil carbon content of these severely eroded soils.  2) Assess the effects of conservation practices and restoration techniques on water runoff and infiltration as soil quality improvement indices. Twelve field plots (33ft X 28ft⁾ are set up at the Ija experiment station in southern Guam for this project.  Plots consist of four treatments, replicated three times.  Treatments include conventional till (CT), conventional till in rotation with sunnhemp (CT/SH), reduced till (RT), and no till (NT) practices.   In this presentation, the methodology as well as up-to-date data will be presented to show the effect of aforementioned management practices on soil conservation as well as on the dynamics of carbon sequestration under each treatment.

Key Words:  Conservation practices, No-till, Soil erosion, carbon sequestration, Guam, Sunnhemp.