fAPAR, SR and NDVI to characterize the vegetative and/or phenologic stages of guava (Psidium guajava']java L.) to forecast its yield

One SPOT satellite image, and field data of 16 guava orchards and 2 blind sites located at Calvillo, Aguascalientes, were used to find if guava's photosynthetic activity rate, could be related with the mean value of spectral indices; the blind sites were a production unit of Agave (Agave tequilana) and the other one an orchard of peach trees (Prunus persica (L)). Two field data collections were performed on March 16 and July 15, 2005. The collected data was: point coordinates, altitude, plantation system and guava's stage. The spectral indices derived were NDVI (Normalized Difference Vegetation Index), SR (Simple Ratio Vegetation) and fAPAR (fraction of Absorbed Photosynthetically Active Radiation). Consistently fAPAR mean values were more adequate than the other two on describe the phenologic stage of guava where the higher mean value point to "cruise fruit" and the minor to "fruit development"; 0.403 and 0.263, respectively. For A. tequilana and P. persica (L), the mean values were 0.120 and 0.236, respectively; the lowest mean value for A. tequilana, was strong influenced by the lacking of any vegetative cover between the rows of plantation. These results support that it is feasible to characterize the phenologic stages of guava using the fAPAR index as first option instead of NDVI and SR. The fAPAR image will play a key role to scale the field data to image extension to estimate guava's yield by developing an integration model.