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.

The injudicious use of water and fertilizer to maximize crop yield not only leads to environmental pollution, but also causes enormous economic losses. For this reason, we investigated the effect of nitrogen (N) (N0 (0), N60 (60 kg ha⁻¹), and N120 (120 kg ha⁻¹)) at different irrigation levels (I0 (0), I1200 (budding 600 m³ ha⁻¹ + kernel 600 m³ ha⁻¹), and I1800 (budding 900 m³ ha⁻¹ + kernel 900 m³ ha⁻¹)) on oilseed flax in the Loess Plateau of China in 2019 and 2020. The objective was to establish appropriate irrigation and fertilizer management strategies that enhance the grain yield (GY) of oilseed flax and maximize water and N productivity. The results demonstrated that irrigation and N application and their coupling effects promoted dry matter accumulation (DMA) and non-structural carbohydrate (NSC) synthesis, and increased the GY of oilseed flax. The contents of NSC in various organs of flax were closely related to grain yield and yield components. Higher NSC in stems was conducive to increased sink capacity (effective capsule number per plant (EC) and thousand kernel weight (TKW)), and the coupling of irrigation and N affected GY by promoting NSC synthesis. Higher GY was obtained by the interaction of irrigation and N fertilizer, with the increase rate ranging from 15.84% to 35.40%. Additionally, in the increased yield of oilseed flax, 39.70–78.06%, 14.49–54.11%, and −10.6–24.93% were contributed by the application of irrigation and nitrogen and the interaction of irrigation and nitrogen (I × N), respectively. Irrigation was the main factor for increasing the GY of oilseed flax. In addition, different climatic conditions changed the contribution of irrigation and N and their interaction to yield increase in oilseed flax. Drought and low temperature induced soluble sugar (SS) and starch (ST) synthesis to resist an unfavorable environment, respectively. The structural equation model showed that the key factors to increasing the GY of oilseed flax by irrigation and nitrogen fertilization were the differential increases in DMA, EC, and TKW. The increases in EC and TKW were attributed to the promotion of DMA and NSC synthesis in oilseed flax organs by irrigation, nitrogen fertilization, and their coupling effects. The I1200N60 treatment obtained higher water use efficiency (WUE) and N partial factor productivity (NPFP) due to lower actual evapotranspiration (ETa) and lower N application rate. Therefore, the strategy of 1200 m³ ha⁻¹ irrigation and 60 kg ha⁻¹ N application is recommended for oilseed flax in semi-arid and similar areas to achieve high grain yield and efficient use of resources.

Interspecies interaction is key to achieving intercropping advantages. However, in semi-arid rainfed agricultural areas, research on how strip width influences interspecific relationships and system productivity in maize–flax intercropping remains insufficient. A three-year field experiment was conducted to assess the impacts of varying strip widths (80, 120, and 160 cm) on system productivity and interspecies interactions in a maize–flax intercropping system. The results demonstrated that the 160 cm strip-width treatment achieved the highest land equivalent ratio (LER) and total system yield, with average increases of 11.3% and 37.5%, 7.3% and 38.8% compared to the 120 cm and 80 cm strip-width treatments, respectively. The improvement in grain yield was primarily attributed to synergistic increases in maize kernel number per ear and 1000-kernel weight, as well as enhanced capsule number per plant, seeds per capsule, and 1000-seed weight of flax. Analysis of interspecific competition dynamics revealed that flax exhibited stronger competitive ability during its later growth stages (kernel-filling and maturity stage) under the 160 cm strip width, with an average increase of 97.2% compared to other treatments. Furthermore, the wider strip width optimized the relative crowding coefficient (RCC) and promoted the recovery effect of maize (RE) after flax harvest. Correlation analysis indicated a significant negative relationship between the intensity of interspecific competition during the maize V3 and V12 stages and flax yield. In conclusion, adopting a 160 cm strip width in the maize–flax intercropping system maximizes overall productivity by optimizing yield components, promoting dry matter accumulation, and balancing interspecific interactions.