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.