As a by-product generated from the pyrolysis of biomass, biochar is extraordinary for improving the soil environment of agricultural fields, improving soil fertility, and promoting nutrient uptake and the utilization of crops. In recent years, breakthroughs in progress have been made regarding the fertility value of biochar and in investigations into the physicochemical properties of soil and into plant nutrient utilization. This review focuses on the physicochemical and biological properties of soil, on soil pollution remediation, on greenhouse gas emissions, and on the effects of biochar on the uptake and utilization of soil nutrients and plant nutrients, as well as on the preparation of biochar, and on biochar produced under different conditions. The results of the relevant studies show that the main characteristics of biochar depend on the biochemical properties and pyrolysis temperature of raw materials, which play an important role in nutrient transport and transformation in the soil. At low temperatures (≤400 ℃), the biochar prepared from manure and waste contains a large amount of nitrogen, which can be used as a nutrient source for plants. In addition, biochar enhances soil fertilizer retention by reducing soil nutrient loss, which in turn promotes nutrient uptake and utilization by crops. By controlling pyrolysis temperature and by optimizing biochar input, one can effectively reduce soil respiration, as well as reduce carbon emissions to achieve the goal of controlling carbon sources and increasing carbon sinks. Therefore, a long-term series of mapping studies on the effects of biochar application on agricultural ecosystems should be conducted, which in turn, it is hoped, will provide a theoretical reference for the physiological and ecological effects of biochar croplands.

Organic fertilizers are an important source of nutrients for improving farmland fertility. To explore high-yield, efficient and green production technology for oilseed flax in dryland agricultural areas, a field split plot experiment was conducted in the semi-arid area of the Loess Plateau in northwest China from April to August in 2020 and 2021. The study compared and analyzed the effects of different nutrient sources and their application rates on water consumption characteristics, grain yield and water use efficiency of oilseed flax. The main plots were fertilizer types (sheep manure, chicken manure and chemical fertilizer), while the subplots were fertilizer application rates (sheep manure: S1-12,500 kg·hm⁻² and S2-25,000 kg·hm⁻²; chicken manure: C1-5800 kg·hm⁻² and C2-11,600 kg·hm⁻²; chemical fertilizer: F1-N 112.5 kg·hm⁻², P 75 kg·hm⁻², K 67.5 kg·hm⁻² and F2-N 225 kg·hm⁻², P₂O₅ 150 kg·hm⁻², K₂O 135 kg·hm⁻²). The results showed that compared with chemical fertilizers, organic fertilizers significantly increased the soil water storage capacity of the 0–160 cm soil layer during the whole growth period of oilseed flax and significantly reduced water consumption. During two growing seasons, the application of 25,000 kg·hm⁻² sheep manure significantly reduced water consumption during the seedling-bud period and green fruit period-maturity period of oilseed flax by 16.13% and 23.19% compared with CK, respectively. Thousand-grain weight, yield and water use efficiency were significantly increased by 14.70%, 48.32% and 61.29%, respectively. These results indicate that the application of 25,000 kg·hm⁻² sheep manure can significantly increase soil water storage capacity of the 0–160 cm soil layer, reduce water consumption during the whole growth period of oilseed flax and thus improve grain yield and water use efficiency of oilseed flax. It is a suitable fertilization technology for the high-yield, efficient and green production of oilseed flax in the semi-arid areas of northwest Loess Plateau.

In order to understand the mechanism of action of oil and fatty acid accumulation and desaturase gene expression in how oilseed flax responds to different fertilization conditions, a three-factor split-plot experiment was conducted to investigate the accumulation trends of oil and fatty acids. The results revealed that soluble sugar (SS) and sucrose (SUC) contents decreased, and the starch (ST) content increased gradually with the grain development and maturity of oilseed flax. The application of sheep manure promoted the accumulation of nonstructural carbohydrates in the grains. Soluble sugar (SS) and sucrose (SUC) contents were negatively correlated with the oil content. Compared with chemical fertilizer, organic manure decreased the total saturated fatty acid but increased the unsaturated fatty acid. Organic manure significantly upregulated the expression of various genes, and fad2a gene expression was higher with the 5.8 t ha⁻¹ chicken manure treatment. The 25 t ha⁻¹ sheep manure treatment was more conducive to the expression of fad3a and fad3b genes and promoted the accumulation of linolenic acid (LIN), and the LIN content increased by 0.64–3.90% compared with other treatments. Consequently, an ongoing anthropogenic sheep manure input may impact the regulation of grain oil quality and yield per unit area.

Various crop rotation patterns can result in differences in nutrient consumption and the accumulation of toxic substances in the soil, indirectly impacting the soil environment and its nutrient supply capacity. Implementing optimized crop planting practices is beneficial for maintaining the favorable physical and chemical properties of farmland soil in the arid area of northwestern China. This study aimed to establish a crop rotation pattern to improve key enzyme activities and soil nitrogen conversion efficiency, as well as understand the underlying mechanism for enhancing nitrogen supply capacity. A field experiment was conducted to study the effect of four flax planting patterns, which included 13 crop rotation patterns with different crop frequencies: 100% Flax (Cont F), 50% Flax (I) (WFPF, FPFW, PFWF, FWFP), 50% Flax (II) (FWPF, WPFF, PFFW, FFWP), 25% Flax (WPWF, PWFW, WFWP, FWPW), on the key enzyme activities and the rate of soil nitrogen conversion, as well as the nitrogen supply capacity. Here, F, P, and W represent oilseed flax, potato, and wheat, respectively. The results indicated that the wheat stubble significantly increased the intensity of soil ammonification and denitrification before planting. Additionally, the activity levels of soil nitrate reductase and nitrite reductase under wheat stubble were significantly increased by 66.67% to 104.55%, while soil urease activity significantly decreased by 27.27–133.33% under wheat stubble compared to other stubbles. After harvest, the activities of soil nitrate reductase and nitrite reductase under the wheat stubble decreased significantly, and the intensity of soil ammonification, nitrification, and denitrification reduced significantly by 7.83–27.72%. The WFWP and FWFP treatments led to a significant increase in soil nitrogen fixation intensity under various crop rotations after harvest and significantly increased the levels of inorganic nitrogen in the soil before the planting of the next crop. This study suggests that the long-term rotation planting patterns WFWP and FWFP can significantly enhance the key enzyme activities of soil nitrogen conversion and significantly improve soil nitrogen conversion before crop sowing. This may increase the rate of soil nitrogen transfer and raise the available nitrogen content of the soil. These findings are crucial for reducing soil nitrogen loss and improving soil nitrogen nutrient supply capacity in dry areas of the Loess Plateau of China.

Organic fertilizers could be useful for agricultural sustainability. Therefore, this study explored green cultivation techniques to improve the grain yield of oilseed flax in dry areas of the Loess Plateau of China. With no fertilization (CK) as the control, the effects of sheep manure (S1: 12.5 t ha⁻¹; S2: 25 t ha⁻¹), poultry manure (C1: 5.8 t ha⁻¹; C2: 11.6 t ha⁻¹), and chemical fertilizers (F1: N 112 kg ha⁻¹, P 75 kg ha⁻¹, K 67.5 kg ha⁻¹; F2: N 225 kg ha⁻¹, P 150 kg ha⁻¹, K 135 kg ha⁻¹) on the growth and development, the grain filling characteristics, and the yield of the Zhangya 2 oilseed flax (Linum usitatisimum L.) variety were compared and analyzed based on a two-factor split plot experiment. The results showed that the application of manure significantly increased the emergence rate (ER) of oilseed flax. Poultry manure increased plant height while sheep manure increased stem diameter. The dry matter production was higher in the 25 t ha⁻¹ sheep manure treatment by 2.47–40.11% compared with that of the other treatments, and it promoted the distribution ratio of dry matter to grains after anthesis. The observed relationship was in accordance with that presented by the logistic equation between grain weight and days after anthesis, and there were significant positive correlations between the 1000-grain weight and the average filling rate (V-ave), the maximum filling rate (V-max), and the growth at the maximum filling rate (W-max). The application of organic manure accelerated the grain filling rate (GFR); under the treatment with 25 t ha⁻¹ sheep manure, V-ave, V-max, and W-max increased by 4.84–22.72%, 1.16–17.54%, and 4.58–22.63%, respectively, and the grain yield and the net income per unit area increased by 6.35–39.25% and 3.04–95.07%, respectively, compared with those under the other treatments. Consequently, the treatment with 25 t ha⁻¹ sheep manure can significantly promote the growth and development of oilseed flax plants, optimize the grain filling characteristics, and increase the grain yield and net income, making it a suitable fertilization technique for oilseed flax in dry areas of the Loess Plateau of China.

Crop rotation aims to improve the sustainability and production efficiency of agricultural ecosystems, especially as demands for food and energy continue to increase. However, the regulation of soil microbial communities using crop rotation with oilseed flax and its relationship with key soil physicochemical driving factors are still not clear. In order to investigate this matter, we carried out a field study lasting four years involving various crop rotation sequences including FWPF, FPFW, PFWF, FWFP, ContF, and ContF1. In addition to evaluating soil physicochemical parameters, we employed Illumina high-throughput sequencing technology to explore the structure and variety of soil microbial communities. The findings indicated a notable rise in pH value with the FPFW treatment in contrast to other treatments, along with significant increases in AP, MBC, MBN, and qSMBC compared to ContF. The number of OTUs in the FPFW, WFPF, FPFW, and PFWF treatments was significantly increased by 4.10–11.11% compared to ContF (p < 0.05). The presence of Actinobacteria and Acidobacteria was greatly impacted by the FPFW treatment, whereas the presence of Actinobacteria and Chloroflexi was notably influenced by the ContF treatment. The soil bacterial community was primarily influenced by TC, pH, and NO₃⁻-N according to correlation analysis. Specifically, the FPFW therapy notably raised the soil pH level while lowering the TC level. Furthermore, the FPFW therapy led to a notable rise in the proportion of Acidobacteria and a significant decline in the proportion of Actinobacteria. These findings provide important theoretical support for using FPFW rotation to regulate soil microbial communities and solve the problems of continuous cropping.