The net primary production (NPP) of a maize (Zea mays L.) field in Poland was estimated, in weather conditions close to those predicted for the middle of the century, given the ongoing changes in the global climate. The average temperature during the maize cropping period (May–September) was 16.9 °C and the total rainfall was 392.5 mm. In such conditions maize NPP reached exceptionally high levels – 3.29 kg m−2, on average. Such an unprecedented level of NPP was achieved as a result of climatic conditions favourable to C4 photosynthesis. The above-ground biomass of maize made up 78% of the total NPP, while the below-ground production was only 7.7% of NPP; weed production was very low, only slightly exceeding 8 g m−2 14.5% of the total NPP consisted of dying and decomposing biomass. Conducted under conditions close to those foreseen for the mid-21st century, this field study enabled NPP levels as well as future relations between plants in different photosynthetic pathways to be predicted. The expected changes in climatic conditions offer good prospects for maize cropping. The beneficial relationship between the above- and below-ground parts of maize and the low percentage of dying and decomposing biomass mean that this plant can be used for silage or biofuel production.