Mechanism of Photothermal Energy on the Growth and Yield of Rice under Water Level Regulation

The flooding caused by heavy rainfall in rice irrigation area and the drought caused by the drop of groundwater level are the research focus in the field of irrigation and drainage. Based on the comparative experiment and farmland water level control technology, this paper studied the average soil temperature under different soil layers (TM), the daily temperature change (TDC), the photosynthetic accumulation of single leaf and canopy in rice, and response of photothermal energy to rice root characteristics and growth factors in the paddy field under drought conditions. The results showed that the peak soil temperature under drought treatment was basically synchronous with the conventional irrigation, and the it was delayed by 2–6 h under flooding treatment compared to the drought treatment. Under different water gradients, the temperature decreased according to T_L > T_CK > T_H (L, H and CK represented water flooding, drought and control treatments), and the TDC was opposite. In addition to milky stage, the daily photosynthetic (Pn) accumulation of single leaf and canopy in the flooding and drought treated paddy fields were lower than conventional irrigation, and had a negative impact on leaf area index (LAI) and yield (YR), but did not form fatal damage. The root characteristic factors, RL (root length), RW (root weight), R-CR (root-canopy ratio) were promoted with drought, and YR under light drought was slightly higher than that under heavy drought. There was a strong positive correlation between TM and R-CR in all rice growth stages, while TDC-5 was negatively correlated with effective panicle number, TDC and R-CR in 20 cm soil layer were positively correlated. The correlation between daily Pn accumulation and YR was low, and the correlation between Pn and YR factors was negative or weak positive or negative. The total Pn was positively correlated with yield factors, and the correlation coefficient was higher than that of daily Pn.