2.1.2 Observations from field destructive sampling
Field destructive sampling was conducted in both years and its regimes in 2019 and 2020 are shown in Table 3. Seven types of observations at the canopy level were conducted: W above, grain weight (W grain), leaf weight (W leaf), aboveground N content (N above), grain N content (N grain), leaf N content (N leaf), and LAI. All observations in 2019 from different treatments were used for model calibration and those in 2020 were used for model validation.
Aboveground plants in an area of 1 and 2.25 m2 in each plot were cut during each field measurement in 2019 and 2020, respectively. At harvest, two sampling sites were selected in each plot and their sampling areas were 2 and 4 m2 in 2019 and 2020, respectively. The total fresh samples were bagged and weighed, while ca. 20% was dissected into component plant parts, including green leaves, yellow leaves, stems and leaf sheaths and panicle chaffs, and grains. The area of fresh green leaves and other green parts like stems was measured immediately using an LI-3100C Area Meter (Li-Cor, Lincoln, NE, USA). The dissected plant organs were weighed after oven-drying at 70 oC until constant weight and then ground to powder to assess N concentration using the Micro-Kjeldahl method. The N content in each plant organ was calculated as the product of their corresponding weight and N concentration. As all green parts are considered as functional leaves in GECROS (Yin and van Laar, 2005), the measured LAI,W leaf and N leaf were adjusted correspondingly following equations Eqns S1-S3 to make the crop model simulations and field measurements comparable.