[Effects of spraying P and K fertilizers during panicle primordium differentiation stage on cold resistance, yield and physiological characteristics of early rice].

Super hybrid early rice variety Ganxin 203 was used as test material, and four foliar spraying treatments were set using clear water as the control group (CK), and 3 concentrations of potassium dihydrogen phosphate (KHPO) with 0.1% (P1), 0.3% (P3), 0.5% (P5) and po-tash (MH). The effects of spraying P and K fertilizers on the leaf temperature, yield and physiolo-gical characteristics in double-season early rice under low temperature conditions during panicle primordium differentiation stage were studied. The results showed that during the low temperature period 6:00-18:00, rice leaf temperature under the different treatments with potassium dihydrogen phosphate and potash was higher than that of CK. Leaf chlorophyll content and net photosynthetic rate (P) of rice plants decreased gradually with the treatments under low temperature, while the reduction range was the smallest in treatment P3. The activities of the antioxidative enzymes varied to different extents, and the increase range for the activities of superoxide dismutase (SOD) and peroxidase (POD) in treatment P3 were higher than those in the other treatments. The decrease range of the activity catalase (CAT) in treatment P3 was lower than that in the other treatments. At the end of low temperature treatment, malondialdehyde (MDA) content was the highest in CK. Under low temperature, foliar spraying of potassium dihydrogen phosphate or potash could improve dry matter accumulation to varying degrees and achieve the purpose of slowing down the yield decrease, among which treatment P3 was the best. It could be found from the yield components that the total grains per panicle, seed setting rate and 1000-grain mass were significantly improved for all treatments compared to CK. The application of foliar spraying of 0.3% potassium dihydrogen phosphate was the most effective agronomic measure to enhance the resistance to low temperature during panicle primordium differentiation stage for double-season super hybrid early rice.