Maize LAI values at each point were obtained by acquiring upward looking hemispherical photographs from beneath the maize canopy using a smartphone digital camera equipped with a fish-eye lens (iPhone 4S with Rollei Fisheye). The photographs were acquired at a height of about 200 mm from the soil, above the weed canopy, in order to capture only maize LAI. The processing of the hemispherical photographs was carried out using the CAN-EYE software (Demarez et al. 2008), which calculates the effective LAI from the gap fraction estimated from the classification of the hemispherical photographs. Concurrently with the LAI data acquisition, the above-ground maize biomass was collected from 1 m2 area at 42 different locations in the fields in 2014 and at 60 locations in 2015. The maize samples were weighted in the field and then dried in an oven for 48 h to obtain dry biomass. The relationship between LAI and dry maize biomass was used to estimate maize biomass at the points in which only LAI and not biomass had been measured, according to the equations shown in Fig. 4. Two different equations were used for the 2 years, since the harvest was carried out much later in the second year as compared to the first, thus the maize growth stage was different. It should be noted that the use of these regression equations entails a root mean square error of 2.80 t ha-1, but it was not feasible to collect maize biomass data in 65–82 points per field in a reasonable amount of time to avoid the introduction of perhaps even higher experimental error.