As expected, photoperiod extension during the post-flowering phase prolonged its duration with respect to the control with the concomitant increases in cumulative photosynthetically active radiation and above-ground biomass production. This indivisible increment in cumulative radiation and biomass due to photoperiod extensions generally overshadows possible direct photoperiodic effects on yield determination that are independent of the extra cumulative radiation due to the extension of the post-flowering phase. The simultaneous photoperiod extension and shading treatments used in this work allowed us to analyse soybean yield determination in response to photoperiod extension somewhat independently of the increased cumulative radiation.