Rice (Oryza sativa L.) is highly sensitive to cold stress, which leads to large reductions in rice yield at the booting stage. In this study, Kongyu131 and Kenjiandao6 rice cultivars with different levels of cold stress sensitivity were sprayed with diethylaminoethyl hexanoate (DA-6) concentrations of 500, 200, 20, 2, 0.2, and 0 mg/L one day before undergoing cold water stress (CWS). We analyzed changes in yield and its factors, dry matter production, stem characteristics, and physiological and biochemical characteristics of the rice plants. The results showed that DA-6 increased peroxidase activity, delayed nitrogen and chlorophyll degradation, maintained soluble protein and potassium contents, and suppressed the accumulation of malondialdehyde in the leaves of both cultivars under CWS. DA-6 also increased the phosphorous content and superoxide dismutase activity in Kenjiandao6 under CWS; however, in Kongyu131, DA-6 increased the soluble sugar content. In addition, DA-6 treatment increased the weight of the panicle at maturity, and of the leaf, panicle, and stem-sheath at heading in both cultivars. The lengths of the panicle, the top first internode, the export rate of stem-sheath, translocation rate of stem-sheath, and export of stem-sheath from heading to maturity were increased in Kenjiandao6; however, in Kongyu131, DA-6 increased the dry weight ratio of panicle to total plant and reduced the dry weight ratio of stem-sheath to total plant at maturity. Furthermore, DA-6 improved yield in both cultivars, mainly by increasing the grain weight in the inferior grains (IG) and middle grains (MG) under CWS. DA-6 increased the grain weight in the IG and MG in Kenjiandao6 mainly by enhancing the seed setting rate and number of filled grains (NFG) in the IG and MG, and in Kongyu131 by improving the NFG in MG and IG. The optimal concentration of DA-6 to alleviate CWS was 2 mg/L. In conclusion, exogenous DA-6 was effective for maintaining dry matter production and physiology in two early japonica rice cultivars under CWS at booting, thereby improving cold tolerance and enhancing yield. The less cold-tolerant cultivar Kenjiandao6 was more sensitive to the effects of DA-6 and displayed better results than the more cold-tolerant cultivar Kongyu131.

The influence of 2-chloro-6-(trichloromethyl) pyridine (CP) on growth, nitrogen (N) absorption and utilization, and yield of rice were examined to offer a technical reference for enhancing rice yield and efficient production under nitrogen limitation in cold regions. In this experiment, Japonica rice was planted with six treatments: 115 kg·ha⁻¹ N (local conventional application, N115), application of N reduced by 20 % (N92), N reduced by 20 % + 900 g ha⁻¹ CP (N92 + CP), N reduced by 30 % (N80.5), N reduced by 30 % + 900 g ha⁻¹ CP (N80.5 + CP), and no-N fertilizer (N0) were used to study the effects of CP on factors relating to yield. In 2022, compared with N92, N92 + CP significantly increased soil available N content (SAN), N uptake (NU), and N fertilizer utilization efficiency (NUE). These factors contributed to an increase in the leaf area index of all leaves at jointing and the leaf area index of the top three leaves at heading. In 2021, the tiller number per hill, dry matter accumulation (DMA) from jointing to heading, DMA from heading to maturity (DMAH), crop growth rate (CGR) from jointing to heading, and CGR from heading to maturity (CGRH) were increased and thus contributed to an increase in total yield. Compared with N80.5, N80.5 + CP significantly increased tiller number per hill, SAN, and NUE in 2022, while the DMAH, CGRH, and yield were increased in 2021 and 2022. This study indicates that CP can maintain rice yield by increasing NU and NUE even under reduced N rates.