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Spatial variations in soil properties, soil productivity, and crop yield in selected corn producing provinces in Cagayan Valley Region, Philippines
Dissertation Abstract:
The future of food security and nutrition relies on the availability of productive soil resources for cultivation of economically important crops. Soil threats such as loss of soil organic carbon (SOC) and decline in soil productivity occur that may lead to the decline in overall land productivity. This study aims to assess the importance of soil and climatic variables that affect the current levels of SOC (a key soil health indicator) and sequestration potential of different soil types; develop SOC sequestration and soil productivity indices; and formulate policy options for SOC and soil productivity improvement in support to improvement in soil governance. The SHAPE procedure as applied to SOC was used to determine SOC sequestration potential; and machine learning algorithms like random forest in R and SHAP module in Python were used to determine feature importance contributing to actual yield of corn. The current SOC levels are low in Isabela and Cagayan; and only 0.92% in soil types of Quirino; although the maximum inherent SOC potential is 3%. This is lower than the critical threshold limit of 1% SOC for soils in the tropics. Inherent SPIs range from 0.18 to 0.73. Using these SPIs, highest inherent yield of 5.61 t ha-1 is computed in areas with San Manuel silt loam while the predicted potential yield is 6.35 t ha-1, which is higher than the actual average yield of 4.19 t ha-1 from 2019-2021. These results imply that with proper soil management alone, productivity could be increased from 1.42 t ha-1 to 2.16 t ha-1. The SOC is linked to significant positive impact on yield estimation from 2019-2021. Some of the policy options to increase SOC and productivity and improve Soil Governance are: a) signing of an Executive Order (EO) for the implementation of the National Soil Health Program including the national adoption of the FAO normative documents on sustainable soil management; b) drafting of a House Bill on the proposed National Soil Management Act in collaboration with the Legislative Branch; c) preparation of the Department Circular signed by the DA Secretary for the full operationalization of the Philippine Soil Partnership and creation of the Philippine Technical Panel on Soils for the refinement of science-based governance instruments; and d) formulation of the Department Order for the "Recarbonization of Philippine Agricultural Soils," to facilitate the provision of incentives on increasing SOC sequestration and soil productivity.