Agronomic and Economic Potential of Vegetation Indices for Rice N Recommendations under Organic and Mineral Fertilization in Mediterranean Regions

Rice (Oryza sativa L.) farmers in Mediterranean regions usually apply organic or mineral fertilizers before seeding that are supplemented with mineral nitrogen (N) later in the season. In general, the midseason N is applied without consideration of the actual crop N status, which may lead to over-fertilization and associated environmental problems. Thus, the purpose of this study was to design and evaluate a N recommendation approach using aerial images for Mediterranean paddy rice systems. A two-year rice field experiment was established in northeastern Spain, with different rates of pig slurry (PS) and mineral N fertilizer. Multispectral aerial images were taken at the rice booting stage, and several vegetation indices (VIs) were calculated. The VIs showed strong relationships with yield and the relations significantly differed between the PS and mineral fertilization treatments. The strongest relations with yield were obtained with gMCARI(NIR), proposed in this study, (R-2 = 0.67), GNDVI (R-2 = 0.64) and MCARI(NIR) (R-2 = 0.64), indicating the importance of including the green band information. The N recommendation approach generated using the VIs information showed a high success (87.5%) in the preliminary evaluation. The economic and environmental analysis showed that this approach provides a useful tool when compared to the usual farmer practices.