Appropriate irrigation schedules could minimize the existing imbalance between agricultural water supply and crop water requirements (ET_c), which is severely impacted by climate change. In this study, different hydrological years (a wet year, normal year, dry year, and an extremely dry year) in Heilongjiang Province were calculated by hydrological frequency methods. Then, the single crop coefficient method was used to calculate the maize ET_c, based on the daily meteorological data of 26 meteorological stations in Heilongjiang Province from 1960 to 2020. Afterward, the CROPWAT model was used to calculate the effective precipitation (P_e) and irrigation water requirement (Ir), and formulate the irrigation schedules of maize in Heilongjiang Province under different hydrological years. The results showed that ET_c and Ir decreased first and then increased from west to east. The P_e and crop water surplus deficit index increased first and then decreased from west to east in Heilongjiang Province. Meanwhile, the average values of the Ir in were 171.14 mm, 232.79 mm, 279.08 mm, and 334.47 mm in the wet year, normal year, dry year, and extremely dry year, respectively. Heilongjiang Province was divided into four irrigation zones according to the Ir of different hydrological years. Last, the irrigation quotas for the wet year, normal year, dry year, and extremely dry year were 0~180 mm, 20~240 mm, 60~300 mm, and 80~430 mm, respectively. This study provides reliable support for maize irrigation practices in Heilongjiang Province, China.

Precious metal-free NiMoM (M = Pr₂O₃, Cu₂O) catalysts have been synthesized through a simple coreduction method, without any surfactant or support material, and characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The resultant Pr₂O₃- or Cu₂O-modified NiMo catalysts exhibit different structures, which is due to a difference in the synergistic effects of NiMo and the modifying elements. NiMoPr₂O₃ has an amorphous structure, with low crystallinity and uniform particle dispersion, while NiMo@Cu₂O adopts the core–shell structure, where the core and shell are synergistic with each other to promote electron transfer efficiency. The support material-free nanocatalysts Ni₉Mo₁(Pr₂O₃)_0.375 and Ni₄Mo@Cu₂O are both highly efficient compared with bimetallic NiMo catalysts, in terms of hydrogen generation from hydrous hydrazine (N₂H₄·H₂O) at 343 K, with total turnover frequencies (TOFs) of 62 h⁻¹ and 71.4 h⁻¹, respectively. Their corresponding activation energies (Ea) were determined to be 43.24 kJ mol⁻¹ and 46.47 kJ mol⁻¹, respectively. This is the first report on the use of Pr-modified NiMo and core–shell NiMo@Cu₂O catalysts, and these results may be used to promote the effective application of noble metal-free nanocatalysts for hydrogen production from hydrous hydrazine.

To scientifically measure the water environment carrying capacity of Harbin City and its change trend, based on analysis of the implications of the sustainability of the urban water environment’s carrying capacity, an evaluation index system for the sustainability of the water environment carrying capacity of Harbin City was constructed. Most existing evaluation methods rely on static data to construct correlation functions between research objects and rank criteria, while the dynamic nature of the information is not considered enough. In this paper, we use hierarchical analysis (analytic hierarchy process, AHP) to determine the weights of each index of the system and then apply the projection tracing method (projection pursuit, PP) to optimize the determined weights. Combining the set pair analysis posture evaluation method and bias coefficients method to explore the dynamic balance mechanism between different index factor levels, a sustainability evaluation model for water environment carrying capacity integrating informational evolution is constructed. Finally, the applicability of the optimization model is tested by comparing the confidence criterion judging method. The model realizes quantitative evaluation of the carrying capacity of the urban water environment. It provides a new and effective means for accurate and reasonable determination of the coefficient of variance and the number of links and dynamic analysis of the water environment carrying capacity system and judgment of its sustainable development trend. The results show that the weight for water resource quality is 0.55, which is the subsystem with the greatest overall impact on the carrying capacity of the water environment in Harbin. The evaluation level of the set-to-potential eigenvalue for 2010–2017 is biased positive 2, and the rest of the years are quasi 2. The reduced value of the coefficient of oppositeness corresponding to the years 2010–2017 is more significant. The maximum value of the dynamic evolution of the load-carrying capacity level is nearly −0.35. From the vertical comparison of different levels, it is found that the water environment carrying capacity of Harbin City gradually recovered to the normal loadable level over time. This overall shows an improving trend.

An evaluation of soil quality sustainability can support decision making for the sustainable use of land resources. However, certain current problems associated with these evaluations remain unaddressed, e.g., the evaluation indicators do not fully reflect soil quality risks and the evaluation scale is not sufficiently small. In this study, 25,000 spatial grids of dimensions 3 km × 3 km are used to divide the major grain-producing regions in China, namely, the Sanjiang Plain and the Songnen Plain of Heilongjiang. Then, the soil erosion modulus, nutrient balance index, soil organic carbon (SOC) storage, heavy metal soil pollution index and crop productivity are calculated for each grid using the RULSE model, nutrient balance index model, soil type method, geoaccumulation index method and mechanism method, respectively. A spatial grid cluster analysis method is used to thoroughly evaluate and analyze the sustainability of soil quality in each grid. The results show that the overall soil status of the study area is good. The soil and water conservation levels are high, the soils show low levels of contamination, the crop production potential is high and the ratio of highly sustainable to moderately sustainable soils is approximately 2:1. Only 2.74% of the land is rated extremely unsustainable and needs to be restored to a basic level of productivity before subsequent functional restoration can be carried out. This study provides a new method for the fine-scale evaluation of soil quality and contributes to the management of land resources.

Aiming to address a series of problems caused by inefficient nitrogen fixation in soybean within the maize–soybean rotation system under cold-region conditions in Heilongjiang Province, China—such as reduced crop yields, declining soil fertility, and increased dependence on chemical fertilisers—this study investigated the partial substitution of chemical nitrogen fertilisers with bio-organic fertilisers at replacement rates of 10%, 20%, and 30% during soybean cultivation. The treatments included bio-organic fertilisers (OB1, OB2, OB3), inactivated bio-organic fertilisers (O1, O2, O3), Bacillus subtilis (B1, B2, B3), and a control (CK) with the conventional application of chemical fertilisers. In the rotational maize cropping phase, a 50% nitrogen reduction was applied. The results showed that replacing 20% of soybean nitrogen fertiliser with bio-organic fertiliser (OB2 treatment) yielded the most significant increase in productivity and economic return. Compared with CK, the OB2 treatment increased soybean yield by 26.56%, maize yield by 26.69%, and nitrogen fertiliser use efficiency by 3–5%. According to the GRA-TOPSIS model, the OB2 treatment demonstrated the greatest capacity to improve quality and efficiency in the maize–soybean rotation system. At the soybean maturity stage, the OB2 treatment increased soil total organic carbon, available phosphorus, and soil protease activity by 25.36%, 22.20%, and 87.50%, respectively, compared with CK. At maize maturity, soil ammonium nitrogen and soil protease activity increased by 80.24% and 62.47%, respectively. Bio-organic fertilisers combine the benefits of organic fertiliser substrates with those of functional microorganisms. Correlation, cluster, and interaction analyses revealed that the synergistic mechanisms between maize–soybean rotation and bio-organic fertilisers in cold regions are primarily reflected in improved soil quality, enhanced nutrient cycling efficiency, increased nitrogen fixation in soybean root nodules, stimulated microbial activity, and greater resilience to environmental stress. Sustainable agricultural production in cold regions can be achieved through the integrated functioning of these system components. This study provides a theoretical basis for enhancing yield and efficiency in maize–soybean rotation systems under cold climatic conditions.

In this study, we collected soybean inter-root soil (clay soil) from the cold region of Heilongjiang Province, China, screening for cold-tolerant phosphorus- and potassium-solubilizing bacteria by the gradient-cooling-directed screening and design of mixed bacterial agents. This study screened cold-tolerant phosphorus-solubilizing and potassium-solubilizing bacteria by gradient-cooling-directed screening and constructed mixed bacterial agents. We analyzed the strain’s phosphorus/potassium solubilizing capacity, as well as its organic acid secretion ability, to reveal its mechanism of detoxification of phosphorus and potassium. Clay soil from the cold region of Heilongjiang, China, was collected for soybean potting trials. The soybean pot experiment was used to investigate the growth-promoting effects of cold-tolerant strains applied to soybeans and to analyze the effects of changes in soil bacterial activity on soybean growth. A dominant phosphorus-solubilizing bacteria strain P-5 (Pantoea ananatis) was screened, and the amount of phosphorus-solubilizing bacteria was 34.94 mg/L with a PSI (Phosphorus Solubilization Index) of 1.80 for 7 days of incubation at 15 °C. The OD₆₀₀ value (optical density of 600 nm) on the 10th day was 0.61. The dominant potassium-solubilizing bacteria, K-1 (Rahnella aquatilis), solubilized 23.02 mg/L of potassium under the same culture conditions, with a KSI (Potassium Solubilization) of 1.51 and an OD₆₀₀ value of 0.59 on day 10. The dominant mixed bacterial agents H-5 (25% P-5 and 75% K-1), designed with the above two, detoxified phosphorus at 62.58 mg/L and potassium at 37.59 mg/L under the same culture conditions. It was shown that P-2 secretes gluconic acid and P-5 secretes lactic acid to degrade insoluble phosphorus at low temperatures and that K-1 secretes citric acid to degrade insoluble potassium. The soybean pot experiment study showed that the application of phosphorus-solubilizing bacteria (PSB), potassium-solubilizing bacteria (KSB), and mixed bacterial agents (MSB) alone could enhance the relative abundance of Pseudomonas, Rhizobium, and other bacterial genera in the soybean planting soil, compared with the control treatment without bacterial agents (BLK). Indirectly, they can enhance the accumulation of phosphorus and potassium in various organs of soybean, promote the development of soybean leaves and stems, and achieve the effect of promoting production and increasing income. This study has important theoretical value for the replacement of chemical fertilizer application by microbial agents in the cold region of China, and it has important practical and strategic significance for the promotion of income green safety in China’s main grain-producing areas.