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Figure 1. 

Radiation (MJ m⁻² day⁻¹), average daily temperature (°C) during rice growing periods in 2017 and 2018. The climate data regarding daily radiation and air temperature were measured at a meteorological station located within 3 km of the experimental site. The daily solar radiation and temperature were measured by a silicon pyranometer (LI-200, LI−COR Inc., Lincoln, NE, USA) and a temperature/RH probe (HMP45C, Vaisala Inc., Helsinki, Finland), respectively.

Figure 2. 

The response of LN to different N rates in two years 2017 (a), (b), (c) and 2018 (d), (e), (f). (a), (b), (c) and (d), (e), (f) represent N0, N150, N300 nitrogen rates for 2017 and 2018 respectively; Avg. - an average of LN at each nitrogen rate. Comparing the range of the LN at each nitrogen rate between the two years N0 N150 and N300 were 0.4, 0.8 and 0.4, respectively.

Figure 3. 

The LN comparison of Hybrid Indica and Japonica rice type at panicle initiation stage. (a) Expt.1 2017, (b) Expt.2 2018; HI - Hybrid Indica, J - Japonica rice type. Rice type's response to different nitrogen rates for each year is expressed by I and II, and different letters are significantly different at P < 0.05 as determined by the LSD test. There was a significant difference in the first year between HI and J with a range of 0.7 of LN and no significant difference registered in the second year with a range of 0.2 between the rice types.

Figure 4. 

Hybrid Indica and Japonica LN's responses to different nitrogen rate are expressed by I and II, and different letters are significantly different at P < 0.05 as determined by the LSD test. Hybrid Indica increased LN in function of nitrogen rate applications, with a maximum LN at N150 and N300 for both years ((a) 2017; (b) 2018)), and it decreased considerably in plots with less nitrogen rate at N0 registering the lowest LN. On the other hand, Japonica rice LN's response to different nitrogen rates was not as clear and uniform as it was in Hybrid Indica rice in both years.

Figure 5. 

Nitrogen effect on DTP for Hybrid Indica and Japonica rice types. (a), (b), (c) and (d), (e), (f) represent N0, N150, N300 nitrogen rates for 2017 and 2018 respectively. Avg. - an average of time duration from transplant up to panicle initiation. Nitrogen had a significant effect on DTP; however, the DTP had a downtrend in response to high dosages of nitrogen. The averaged values of LN for both years at different nitrogen rates had a range of 2.8, 3.2 and 2.7 for N0 N150 and N300 respectively.

Figure 6. 

Hybrid Indica and Japonica rice type LN and thermal time from transplant up to panicle initiation (TT °C/d). (a) 2017 Hybrid Indica and Japonica rice type, (b) 2018 Hybrid Indica and Japonica rice type, (TT - Thermal Time). The TT values resulted from averaged data of daily temperature. Based on the averaged data of both years Hybrid Indica and Japonica, LN under three different nitrogen rates was reached with less than 1,600 and 2,000 °C/d accumulated temperature respectively. Japonica cultivars required more accumulated daily temperature to reach panicle initiation stage as opposed to Hybrid Indica cultivars.

Figure 7. 

Comparison of DTP between Hybrid Indica and Japonica rice type in response to different N rates. (a) and (b) represent 2017 and 2018 respectively. There was a significant difference between Hybrid Indica and Japonica rice type in (a) and (b) with a range of 4 and 1.9 respectively.

Figure 8. 

Nitrogen effect on Hybrid Indica and Japonica rice types. (a), (b), (c) and (d), (e), (f) represent N0, N150, N300 nitrogen rates for 2017 and 2018 respectively. Avg. - Average of LAR at each nitrogen rate. The LAR had no significant difference between the two years and the ranges at N0, N150 and N300 were 0.1, 0, 0.1 respectively.

Figure 9. 

The LAR comparison between Hybrid Indica and Japonica in response to different nitrogen rates. (a) 2017, (b) 2018. There was no significant difference between Hybrid Indica and Japonica rice type as a response to different nitrogen applications and the range between them in both years was 0.1 and 0.2 respectively.

Figure 10. 

The relationship between LAR and DTP. Linear regression analyses between DTP and LAR in (a) 2017 and (b) 2018. The LAR increases linearly with DTP, R² = 0.1596 and R² = 0.2298 for (a) and (b) respectively.