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【Objective】Based on the evaluation of growth period and grain yield performance of ratooning rice under different cutting heights, suitable varieties were selected for ratooning rice production in North Guangdong.【Method】Thirty-four rice varieties (bred or approved in Guangdong Province) were selected for tests under mid- or low-stubble cutting heights. The growth period, grain yield and yield components under different cutting heights among the tested varieties were investigated.【Result】The main crop yield was 5 210.9-8 566.8 kg/hm2, and grain yield of Huangguanghuazhan 1 was the highest. The ratoon crop yield of low-stubble ratooning rice was 3 335.0-6 357.3 kg/hm2, 16.1% higher than that of mid-stubble ratooning rice (2 084.4-5 940.5 kg/hm2). Qingxiangyou 19 Xiang was the highest in ratoon crop yield under both cutting heights. According to cluster analysis, the ratoon crop yield and total annual grain yield under mid-stubble ratooning rice mode could be categorized to four major groups, namely, high-yield, mid-high-yield, medium-yield, and low-yield levels. Each group contained 4, 7, 18, and 5 varieties for ratoon crop yield and contained 1, 14, 14, and 5 varieties for total annual grain yield under mid-stubble ratooning rice mode. Under low-stubble cutting height, the ratoon crop yield was also categorized to four major groups with 2, 17, 14 and 5 varieties, while the total annual grain yield was divided into three major groups, containing 10, 21, and 3 varieties, respectively. In ratoon season of low-stubble ratooning rice, the growth period was prolonged by an average of 9.1 days, the number of spikelets per panicle was increased, and the effective panicles and seed setting rate were reduced compared with those in ratoon season of mid-stubble ratooning rice. Under mid-stubble cutting height, the ratooning rice regenerated from the 3rd, 4th, and 5th nodes from the top (D3, D4 and D5) contributed 4.7%, 33.3%, and 62.0% of the total grain yield per plant, respectively. Under low-stubble cutting height, the ratooning rice regenerated from D3, D4, and D5 contributed 0%, 11.9%, and 88.1% of the total yield per plant.【Conclusion】If assessed with the criteria of high- or mid-high-level ratoon crop yield and high-level total annual grain yield, 9 rice varieties, including Huangguangyouzhan, Huangguanghuazhan 1, Huangguangtaizhan, Wuyouyuehesimiao, Guang 8 Youjinzhan, Hengfengyou 387, Qingxiangyou 003, Qingxiangyou 132, and Qingxiangyou 19 Xiang are recommended for production of mid-stubble ratooning rice. Ten rice varieties, including Erguangyouzhan 3, Huangguangyouzhan, Huangguanghuazhan 1, Huangguangtaizhan, Yuehesimiao, Nanjingzhan, Yuetaiyouzhan, Wuyouyuehesimiao and Guang8youjinzhan are suitable for production of low-stubble ratooning rice. For mid-stubble ratooning rice, new tillers mainly regenerate from the 4th nodes from the top and other lower nodes below. For low-stubble ratooning rice, new tillers mainly regenerate from the 5th nodes and other lower nodes below.

【Objective】In order to further enhance grain yield of rice and nitrogen (N) use efficiency (NUE), N fertilizer was reduced and topdressing was delayed, together with alteration in row and plant spacing and planting density.【Method】In two late seasons, comparison trials were conducted with 8 treatments, including zero applied N (T1), farmers' practice (T2, control), 3 moderately-delayed N topdressing (T3-T5) and 3 highly-delayed N topdressing (T5-T8). T3-T8 also had alteration in N application rate, planting density and row and plant spacing.【Result】In comparison to T2, the average grain yields under T3-T5 were increased by 29.7% and 15.9%, and those of T6-T8 were increased by 26.4% and 18.6% in two late seasons, respectively. In both late seasons, nitrogen uptake and plant growth under T3-T5 and T6-T8 were slower before panicle initiation and they were both increased or accelerated thereafter. Based on average results in two late seasons, leaf area indexes at heading stage were enhanced by 8.5% and 11.8% respectively under T3-T5 and T6-T8 compared with that under T2. Leaf nitrogen contents at heading stage were enhanced by 16.8% and 23.5%, respectively. The numbers of panicles per hectare were increased by 14.5% and 15.2%, panicle size remained unchanged or was increased by 12.5%, sink sizes were increased by 13.6% and 29.3%, seed setting rate was enhanced by 9.0% or remained the same, 1000-grain weight remained identical or was decreased by 9.0%, biomasses were increased by 14.8% and 15.5%, and harvest indexes were increased by 7.2% and 6.4%, respectively. The total amounts of N uptake were increased by 27.6% and 40.7%, N uptake efficiencies were increased by 85.9% and 124.2%, agronomical efficiencies were increased by 99.1% and 102.5%, and partial factor productivity was increased by 32.1% and 36.2%, respectively. Additional N input, dense planting and alteration in row and plant spacing had little effect on yield and NUE. Highly-delayed N topdressing could further expand sink size and improve NUE, but could not enhance grain yield anymore.【Conclusion】With reduced N input, both source and sink of rice were substantially enlarged, and the yield and NUE were dramatically increased under moderately-delayed and highly-delayed N topdressing.

Fish pond rice planting is an agricultural production activity that uses aquaculture ponds to grow rice. The development of fish pond rice planting technology can keep the aquaculture area, expand the rice planting area, improve food security, and reduce pollution from aquaculture tail water. In the early season of 2022, we conducted a fish pond rice planting experiment in Guangzhou and achieved initial success. The tested rice varieties were Yuetai Youzhan, Huangguang Youzhan, Meixiangzhan No. 2, Taifengyou 208, Guanghong No. 3, Yuexiang 430, Yuenong Simiao, Wushan Simiao, and Nanjing Xiangzhan. The aquaculture varieties were largemouth black bass, Australian freshwater lobster, crucian carp and yellow catfish. The results showed that there was significant difference in grain yield among tested rice varieties under fish pond cultivation and the difference was much greater than that under field cultivation. The yield of Yuexiang 430 was the highest, reaching 390.8 kg/667m2, which was 148.6% higher than that of Taifengyou 208. The four aquaculture varieties all performed well, with high survival rate and fast growth speed, among which the Australian freshwater lobster performed the best. At present, there are still some critical problems such as high cost, lack of technical standards and lagging behind in basic research in fish pond rice planting. Coordinated efforts should be made to enhance low-cost floating bed development, improve rice and fishery matching, screen out more rice varieties, optimize fertilizer management and pest control, manufacture or adapt supporting machinery and equipment, and strengthen relevant theoretical researches. Finally, the green, high-yield and high-efficiency fish pond rice planting procedures and standards should be established through technical integration. With the deepening of research and the maturing of technologies, the fish pond rice planting technology will make increasing contributions to food security, farmers' income increase, environmental protection and beautiful countryside construction in China, especially in the southern regions.