TABLE 1.
Environmental covariates (ECs) description, modified from Lecomte (2005) and Heslot et al. (2014).
| Code | Variable description | Category |
| ave.glorad | Average global radiation (MJ/m2) | Radiation |
| ave.temp | Average temperature (°C) | Temperature |
| ave.vpd | Average vapour pressure deficit (VPD, kPa). VPD measures difference between air moisture and potential moisture and is related to water loss | Water/evapotranspiration |
| cumglorad | Accumulated global radiation (MJ/m2) | Radiation |
| ratrdtmp | Ratio between global radiation (MJ/m2) and temperature (°C) | Photothermal ratio |
| cumpospetp | Accumulated positive precipitation (mm) – evaporation (mm) | Water |
| cumnegpetp | Accumulated negative precipitation (mm) – evaporation (mm) | Water |
| cumpetp | Accumulated total precipitation (mm) – evaporation (mm) | Water |
| cumntdryd | Number of total dry days [precipitation (mm) ≤ evaporation (mm)] | Water |
| cumnsti4 | Accumulated temperature (°C) lower than −4°C | Frost/temperature |
| cumndt0 | Number of days with minimum temperature (°C) lower than 0°C | Frost/temperature |
| cumsti0 | Accumulated temperature (°C) lower than 0°C | Frost/temperature |
| cumprec | Accumulated precipitation (mm) | Water |
| cumvpd | Accumulated vapour pressure deficit (kPa) | Water/evapotranspiration |
| GDD | Growth degree days estimated as the thermal sum of daily average temperature over 0°C | Temperature |
| ndi10m | Number of days with radiation lower to 1,045 J/cm2 | Radiation |
| sri10m | Sum of daily radiation (MJ/m2) when radiation is lower to 1,045 J/cm2 | Radiation |
| pvt | Plant available water (%) | Soil/water |
| wscmm | Water storage capacity (mm) | Soil/water |
| claynor | Sand content (%) | Soil |
| fsandno | Fine sand content (%) | Soil |
| gsandno | Coarse sand content (%) | Soil |
| kulstof | Carbon content (%) | Soil |
| siltnor | Silt content (%) | Soil |
| Ks_250 | Saturated hydraulic conductivity (%) | Soil |
The ECs for the categories radiation, temperature, frost, photothermal ratio, water and evapotranspiration were computed each 100 GDD for the complete growth cycle starting from the sowing date. The ECs for the category soil were available at all localities for four depths: 0–30, 30–60, 60–100, 100–200 cm. The ECs from the different categories were used together to describe the environmental conditions in each year-location combination.