Evaluating nutrient uptake and site-specific nutrient management zones in rice in Costa Rica from plant tissue and soil sampling is expensive because of the time and labor involved.  In this project, a range of measurement techniques were implemented at different vintage points (soil, plant and UAVs) in order to generate and compare nutrient management information.  More precisely, delineation of site-specific nutrient management zones were determined using 1) georeferenced soil/tissue sampling, 2) proximal soil sensing (soil pH, Electrical Conductivity ECa, and dual-wavelength optical measurements) and 3) multispectral (blue, green, red, red edge, near IR narrowband wavelengths) and thermal images (0.1 oC temperature resolution) generated from UAV platforms.

New nutrient management plans were designed and applied based on site-specific soil/plant deficiencies and nutrient uptake at commercial scale.  Two treatments were implemented to evaluate the benefits of site-specific nutrient management, namely i) Business-as-usual (control) where the conventional fertilization was maintained (4.33 ha) and ii) Optimized fertilization using nutrient deficiency maps (soil and plant) and variable rate applications (4.56 ha). The zoning maps were used to apply macro and microelements according to soil deficiencies and crop needs.

Delineation maps have shown to be a useful approach to guide fertilization operations.  The grain yield was 4.72 Mg/ha for the conventional fertilization and 5.62 Mg/ha for the optimized site-specific fertilization resulting in a production yield increase of 18.9%.  The yield of the optimized fertilization was 42.6% higher than the Costa Rican average.  A cost-benefit analysis was carried out indicating that the optimized site-specific fertilization resulted in gains of USD $188/ha per rice cycle compared to conventional fertilization practices.

This study indicates that this new multi-sensor and data fusion approach is a useful technique to improve yield, generate gains (after cost of data generation), and to optimize rice production.