The addition of biochar-based organic fertilizer (BOF) can improve sugar beet yield, but its effects on the growth of sugar beet and on soil quality at different densities remain unclear. Six treatments, comprising two densities D1 and D2 (80,000 and 90,000 plant ha⁻¹) and three application rates B1, B2, and B3 (2.75, 3.25, and 3.75 t ha⁻¹) of BOFs + mineral fertilizer, respectively, are investigated in this research. The mineral fertilizers are typically used to supplement the total N, P₂O₅, and K₂O deficiencies. The BOFs were used in the soil before sowing, and the mineral fertilizer was added to the soil after the first pair of true leaves was grown. At 160 days after sowing (DAS), the root-to-shoot ratio under the D2B2 treatment was significantly higher than that under the other treatments. The effect of density on the photosynthesis rate of sugar beet was not significant. The BOF application amount and density exerted interaction effects on soil physicochemical properties and the activities of different soil enzymes affecting each other. Both the D2B2 and D2B3 treatments reduced the content of NO₃^–-N in the 40–60 cm soil layer. Combined 90,000 plants ha^–1 with 3.25 t ha⁻¹ BOFs can increase the soil nutrient content of the 0–60 cm soil layer, improve the rhizosphere soil environment, promote the uniform distribution of dry matter, and increase sugar production.

Maize (Zea mays L.) is the largest grain crop in Heilongjiang Province. Carbon-based fertilizer is a mixed fertilizer produced by adding a certain proportion of chemical fertilizer with biochar as the loading substrate. In this study, the effects of carbon-based fertilizer on the rhizosphere soil microenvironment and maize root system were discussed. Two maize varieties, Xianyu 335 and Jingke 968, were selected and six treatments were set as follows, including no fertilization (CK1), conventional fertilizer (CK2) and the amount of carbon-based fertilizer, which were 3 t/hm², 3.75 t/hm², 4.5 t/hm² and 5.25 t/hm², respectively. The results showed that carbon-based fertilizer increased the total root length, root volume, root area and root tip number of maize, and the root length, root volume, root area and root tip number of 4.5 t treatment performed better at all stages, which was significantly higher than that of chemical fertilizer. On 16 August (early filling stage), most of the root color changed from milky white to dark brown, the root clarity decreased, the number of roots decreased, the root volume significantly decreased and the root began to age, while the number and volume of roots treated with the carbon-based fertilizer remained stable, the root color was milky white, the morphological structure was clear and there was basically no aging. The carbon-based fertilizer treatment significantly increased the root biomass of 0–15 cm above the plant, 15–30 cm and 30–45 cm between the plants and 0–15 cm between the ridges, forming a wide and deep high-yield root system. The carbon-based fertilizer significantly increased the bleeding rate. On 8 July (jointing stage), Xianyu 335 and Jingke 968 reached the maximum value at the 3 t and 3.75 t treatments, respectively. The carbon-based fertilizer treatment had no significant effect on the amino acid content, but significantly increased the amino acid transport rate on 8 July (jointing stage) and 16 August (early filling stage). The transport rate of inorganic phosphorus gradually decreased with the advancement of the growth process. On 8 July (jointing stage), the ammonium nitrogen content and transport rate of the two varieties reached the maximum value at the treatment of 4.5 t and 3.75 t, which was significantly higher than the treatment of chemical fertilizer and no fertilizer, and showed a gradual downward trend with the advancement of the growth process. The soluble sugar content was relatively low in the early stage and increased rapidly on 4 September (waxy ripening stage). Both varieties reached the maximum value at 4.5 t treatment, and the transport rate reached the maximum value at 3.75 t treatment, which was significantly higher than that of the chemical fertilizer treatment. In conclusion, the carbon-based fertilizer significantly increased the yield of maize, and the yield of maize under the 4.5 t treatment reached the maximum, which was 15.02% and 18.24% higher than that of the chemical fertilizer treatment, respectively.