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The soil is the primary source of selenium intake for humans and animals. Investigating selenium's migration from soil to crops and the human body holds significant scientific value in assessing agroecosystems and human well-being. This study analyzes selenium levels in soils, crops, and human hair in Aksu, Xinjiang, a selenium-rich farmland, focusing on the Selenium-Crop-Hair System (SCHS). In Aksu's selenium-rich farmland, soil selenium ranged from 0.09 to 4.60 mg/kg, averaging 0.356 mg/kg. Among crops, average selenium content ranked as follows: wheat (0.084 mg/kg) > rice (0.079 mg/kg) > maize (0.065 mg/kg) > carrot (0.058 mg/kg) > walnut (0.044 mg/kg) > apple (0.042 mg/kg) > jujubes (0.039 mg/kg). Human hair displayed selenium content ranging from 0.34 to 0.57 mg/kg, averaging 0.46 mg/kg. Overall, selenium levels in soils, crops, and human hair fall within selenium-moderate to selenium-sufficient ranges. Comparatively, bioaccumulation factors (BAF) of rice/soil (0.22) and hair/soil (1.28) in Aksu surpass those in other Chinese regions, indicating higher selenium bioavailability in the northwestern, China. Rice and carrots, under intense irrigation, exhibited a strong correlation in selenium content among crops, rhizosphere soil, and background soil. Conversely, weak correlations were observed between the edible part of apples, walnuts, jujubes, wheat, maize, rhizosphere soil, and background soil. Intensively irrigated farmland showed higher selenium content in rhizosphere soil and crops compared to rainfed fields, suggesting that irrigation, potentially coupled with intercropping and residue management, may enhance selenium migration and circulation in soils. However, crop selenium content may be more influenced by biological absorption characteristics. • Northwest China has higher selenium bioavailability. • Irrigation is beneficial for the circulation of selenium in farmland. • Selenium content in root soil is controlled by cultivation mode. • The selenium content of crops depends on their biological species. [ABSTRACT FROM AUTHOR]

Intercropping has gained widespread adoption among farmers due to its ability to yield higher outputs. The primary reasons behind the yield advantage of intercropping systems are the border effects. Among various factors influencing the inter-species relationship, nitrogen (N) plays a crucial role. However, yield and border effects of wheat/maize intercropping at different N levels have been poorly studied, especially under rainfed conditions with different rainfall year types. The objective of this study was to compare the contribution of different crop strips to yield at different N levels and to explore the impact of different precipitation on crop physiological characteristics and water use of intercropping systems in rainfed areas. A field experiment was conducted between 2019 and 2021 in Yangling, Shaanxi Province, adopting a two-factor design, with the main treatment as planting pattern (sole wheat; sole maize; wheat/maize intercropping), and the secondary treatment as three N levels (0, 180, 300 kg ha−1 for wheat and 0, 235, 360 kg ha−1 for maize). Results showed that, intercropping increased total yield and land productivity, with a land equivalent ratio of 1.05–1.15. The intercropping system led to increased water consumption during crop growth, however, it also exhibited a notable improvement in water use efficiency, with a 5.2–16.9% increase compared to sole wheat cultivation. During the symbiotic period, intercropping wheat showed competitive advantages, resulting in yield increments of 16.4–31.2% over the two-year period. Border row wheat contributed 63.7% of the total production, with the increase in yield mainly attributed to an increase in the number of spikes and 1000-kernel weight. On the other hand, the intercropping maize showed a competitive disadvantage during the symbiotic period. The leaf area index, net photosynthetic rate, and yield of border row maize were comparatively lower than those of inner maize. However, no significant differences were observed between the yield of inner row maize and that of sole maize. After the wheat harvest, the intercropping maize resumed growth. The growth of intercropping maize was constrained by N and moisture conditions. In 2020 (Precipitation: 572.8 mm), the yield of intercropping maize increased by 3.2% compared to sole maize under N2 treatment, but in 2021 (Precipitation: 251.4 mm), the yield of intercropping maize decreased by 1.1%− 4.3%. Wheat/maize intercropping has clear advantages in land use in the Northwest China due to the availability of more resources for wheat/maize intercropping, especially in the border rows of wheat. The recovery of late-sown crops is limited by water and nitrogen, and increasing the water and nitrogen supply of late-sown crops can better play the advantages of intercropping. This study demonstrates that the contribution of intercropping system component crops to yield, and provides practical guidance for improving the productivity of wheat/maize intercropping systems in Northwest China. • The border effects of wheat/maize strip intercropping were studied. • Border wheat rows received better light, nutrition and moisture conditions. • The border wheat contributed 63.7% of the total wheat output. • The recovery growth of maize was affected by nitrogen and precipitation. • Wheat/maize intercropping improved land productivity in Northwest China. [ABSTRACT FROM AUTHOR]