Legume Genomics and Genetics 2025, Vol.16, No.6, 253-269 http://cropscipublisher.com/index.php/lgg 262 varieties are early-maturing or medium-early maturing types. In the past, the soybean planting density in Qiqihar was relatively low, about 200,000 plants per hectare, and the yield was around 1.8 tons per hectare. In recent years, with the implementation of the soybean revitalization plan, researchers have tried to increase the yield of soybeans in the north by increasing density and improving fertilization. In the dense planting and matching cultivation experiment of new and superior high-protein soybean varieties carried out by the Heilongjiang Academy of Agricultural Sciences in Qiqihar, the yield performance under different sowing periods and planting density combinations was compared. The results show that early sowing at the right time (early May) can make full use of the growth period and make the yield higher than the conventional sowing period; at the same time, under early sowing conditions, the density increased significantly from 250,000 to 350,000 plants per hectare, and the yield increase decreased when it continued to increase to 450,000. Comprehensive analysis shows that the optimal cultivation plan for local early-maturing varieties is to sow before May 5, with a density of about 300,000 plants per hectare. Based on this plan, large-scale demonstrations were carried out, and the average soybean yield per mu in multiple test sites in Qiqihar reached 300 kg, which is more than 10% higher than the conventional yield of farmers. In terms of fertilization management, a strategy of nitrogen-based, phosphorus-stabilizing and potassium-increasing was adopted according to the nutrient characteristics of black soil: 40 kg of pure nitrogen, 60 kg of phosphorus fertilizer, and 45 kg of potassium fertilizer were applied per hectare, and molybdenum fertilizer was applied in combination with the molybdenum requirement of soybeans. No nitrogen fertilizer was applied in the later stage to prevent vigorous growth and lodging (Hao et al., 2023). Under this fertilization measure, the nutritional growth and reproductive growth of densely planted soybean groups were coordinated, the number of effective pods per plant decreased slightly, but the total number of pods in the group increased significantly; more importantly, the protein and fat content of the grains increased simultaneously, and there was no high yield accompanied by a decrease in quality. Field surveys showed that the pods of the group under high density were more evenly distributed, and there were more effective pods in the lower part, which increased the harvest index. The experiment also paid special attention to economic benefits: due to the increase in soybean seed and fertilizer input, the cost increased slightly, but due to the increase in yield and the support of the national soybean subsidy policy, the net income still increased. Farmers reported that as long as the yield per unit area increased by more than 0.1 tons/hectare, the cost of dense planting and increased fertilization could be offset, and the yield increase in the demonstration generally exceeded 0.2 tons/hectare, with significant income increase benefits. Qiqihar's practical experience has proved that in high-latitude black soil areas, through dense planting of suitable varieties and precise fertilization, it is entirely possible to break through the traditional soybean yield limit and achieve a double increase in yield and quality. This has set a typical example for the large-scale promotion of high-yield and high-quality soybean cultivation in Northeast China. Figure 1 Illustration of peanut sowing and fertilization location (Adopted from Wang et al., 2022) Image caption: L1—Row distance 25 cm; L2—Rridge distance 85 cm; H1—Ridge height 15 cm; H2—Sowing depth 4 cm; H3—Fertilization depth at fruiting layer 8 cm; H4—Fertilization depth at root concentrated layer 16 cm (Adopted from Wang et al., 2022)
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