## Materials and Methods  
### Field Plots  
We used field data from 162 plots with six different crop species: oat (_Avena sativa_ L.), turnip rape (_Brassica rapa_ L. ssp. _oleifera_ (DC.) [PERSON]), barley (_Hordeum vulgare_ L.), lupin (_Lupinus angustifolius_ L.), wheat (_Triticum aestivum_ L. emend Thell), and faba bean (_Vicia faba_ L.) (Figure 1). The plots were located at the Patoniitty and Porvoontie agricultural experimental sites on the Viikki campus of the University of Helsinki, Finland (60.22\({}^{\circ}\) N, 25.02\({}^{\circ}\) E, Table 1, Figure 2). The plots varied in soil type, planting density and fertilization (Table 1).  
We applied the species-specific leaf tilt angle distributions determined at the same experimental site by [PERSON] et al. (2011). They measured the leaf tilt angle, defined as the angle between the leaf surface normal and the zenith, from leveled photographs taken approximately 1 m from the edge of the plots growing the crops. Leaves orthogonal to the camera viewing direction (i.e., with their normals inside the image plane) appeared in the photos as narrow lines. [PERSON] et al. (2011) determined the directions of these leaves (lines in photographs), thus quantifying their tilt angle distribution. Assuming that leaves were distributed uniformly in the azimuth direction, the tilt angle distribution was taken as representative of the whole canopy and the species in general. Finally, the leaf angle distribution was used to calculate leaf mean tilt angle (MTA).  
We used the leaf chlorophyll a and b content (Cab) determined with a SPAD meter (SPAD-502, Minolta, Japan) on 19-22 July 2011 and reported by [PERSON] et al. (2013). After a single leaf was inserted into the SPAD meter, the instrument determined its transmittance of red light quantified as a 'SPAD value'. [PERSON] et al. (2013) converted these SPAD measurements to absolute chlorophyll content using a general relationship available in the literature [PERSON] et al. (2013)  
\[\text{Cab}\ (\mu\text{g}\ \text{cm}^{-2})=0.0893\ (10^{\text{SPAD}^{2,0 5}}). \tag{1}\]  
Altogether, \(15-30\) SPAD readings were converted (Equation (1)) and averaged for each plot [PERSON] et al. (2013).  
The leaf area index data reported by [PERSON] et al. (2011) were applied in this study. [PERSON] et al. (2011) used measurements with a SunScan SSI ceptometer bar (Delta-T Devices, Cambridge, UK) on 20-21 July 2011 from the study plots. The ceptometer bar determined the canopy-penetrated photosynthetically active radiation under a clear sky using 64 miniature sensors. Within the instrument hardware, the readings were averaged and, using data from a separate top-of-canopy sensor, converted to the canopy transmittance of the direct solar beam. [PERSON] et al. (2011) used the standard method for converting canopy transmittance to LAI (based on the Beer-Lambert law of radiation extinction) with extinction coefficients determined from the leaf angle measurements described above. The mean values of LAI, MTA, and Cab for the plots used in this study are presented in Table 1, and further details have been reported by [PERSON] and [PERSON] [PERSON] and [PERSON] (2012).  
We used the soil spectral reflectance measurements by [PERSON] and [PERSON] [PERSON] and [PERSON] (2012). They determined the mean soil spectral reflectance from harvested plots using a handheld Analytical Spectral Devices spectrometer (ASD Inc., Boulder, CO, USA) and a white Spectralon reflectance panel under cloudless skies on 7 October 2011. [PERSON] and [PERSON] [PERSON] and [PERSON] (2012) corrected the measured reflectance for differences in the solar angle between the measurement times in July and October.