To investigate the distribution characteristics of selenium (Se) in mountainous soil-crop systems and examine the threshold value of Se-rich soil, 275 soil samples and 153 associated crop samples (rice, maize, tea, nuts, konjac, mushrooms, buckwheat, and coffee) were collected in Ximeng County, a typical mountainous area in southwest China. The total Se, available Se, organic matter, pH, sampling point elevation, and crop Se content were analyzed to examine the distribution characteristics of soil Se and the ability of primary crops to enrich Se in Ximeng County. Random forest and multiple regression models were established to identify the factors influencing the available soil Se and the crop Se enrichment coefficient. Finally, the Se-rich soil threshold was examined based on the total Se, available Se, and Se content in primary crops (rice, maize, and tea). The results showed soil Se resource abundance in the study region, with high Se soil accounting for 64.72% of the entire area. The soil Se content displayed significant spatial autocorrelation. The average Se enrichment coefficient of the main cultivated crops included mushrooms > nuts > rice > coffee > tea > maize > buckwheat > konjac. The total Se content in the soil had the highest impact on the available Se content in the soil and the Se enrichment coefficient of crops. A Se-rich soil threshold of 0.3 mg·kg⁻¹ was used for rice and maize, while that of tea was 0.4 mg·kg⁻¹. This result provided a theoretical basis for developing and utilizing Se resources in mountainous soil in southwestern China and dividing the Se-rich soil threshold.

The southwestern region of China is one of the major maize (Zea mays L.)-producing areas and a concentrated zone of farmland contaminated by heavy metals (HMs). Selection of maize varieties with low accumulation of HMs under complex HM pollution conditions is one the most feasible and effective ways for safe utilization of HM-polluted farmland. In this study, we conducted field experiments to investigate the differences in biological traits among 28 local maize varieties under combined soil pollution with Cd, Pb, As, Cr, and Hg. We analyzed the absorption, accumulation, and transport characteristics of Cd, Pb, As, and Cr in various parts of the maize plant (Hg was not detected in any part of maize plants) and explored the relationships of HM contents in different parts of maize with soil HM contents through cluster analysis, correlation analysis, and principal component analysis. The results indicated that among different biological traits of maize, root length, root dry weight, and plant height were the most significantly influenced by soil HM content, while stem dry weight was the least affected. The accumulation capacity of various maize parts for HMs followed the order of grains < stems < cobs < leaves < roots, while the transport capacity followed the order of root–grain < root–stem < cob–grain < stem–cob < stem–leaf. In addition, the accumulation capacity of maize grains for HMs followed the order of As < Cr < Pb < Cd. Different HMs exhibited synergistic effects in various maize parts, except for the stem, particularly in the grains. A synchronous transport mechanism was observed for As and other HMs in different parts. The accumulation of HMs in maize was primarily derived from human activities such as the extraction, storage, and smelting of non-ferrous metals, while the HMs in soil parent material and weathering products played a secondary role. The yield of the tested maize varieties ranged from 7377.6 to 11,037.0 kg·hm⁻², with M5 (Haoyu 1511) achieving the highest yield. M2, M4, M5, M9, M10, M21, and M25–28 were identified as suitable varieties with low Cd, Pb, As, and Cr accumulation for popularization in HM-contaminated soils in southwestern China due to their low accumulation of HMs.

To explore strategies for the safe utilization of farmland co-contaminated with cadmium (Cd) and lead (Pb), this field study systematically evaluated the impacts of humic acid (HA) and potassium fulvate (PF) at different application rates (0, 1500, 3000, and 4500 kg·ha⁻¹) on the growth, yield, and translocation of Cd and Pb within the soil–plant system of maize (Zea mays L.). The results showed that while HA and PF did not significantly alter total soil Cd and Pb concentrations, they markedly reduced their bioavailable fractions. This mitigation of heavy metal phytotoxicity significantly promoted maize growth and yield, with the high-dose HA treatment increasing yield by a maximum of 32.9%. Both amendments dose-dependently decreased Cd and Pb concentrations, bioconcentration factors (BCF), and translocation factors (TF) in all maize tissues, particularly in the grains. At equivalent application rates, PF was slightly more effective than HA in reducing heavy metal concentrations in the grains. Notably, a significant positive correlation was observed between Cd and Pb concentrations across all plant parts, confirming a synergistic accumulation and translocation mechanism. This synergy provides a physiological explanation for the broad-spectrum immobilization efficacy of these humic substances. In conclusion, applying HA and PF presents a dual-benefit strategy for increasing yield and reducing risks in Cd- and Pb-contaminated farmlands. This study proposes a differentiated application approach: PF is the preferred option when ensuring food-grade safety is the primary goal, whereas high-dose HA is more advantageous for maximizing yield in soils with low-to-moderate contamination risk.

Cadmium (Cd) in contaminated soil not only enters surface water via rainfall runoff but also penetrates groundwater, adversely affecting human health through the food chain. This research examined three kinds of soil from Luoping County in southwestern China, with different Cd pollution levels. Simulated rainfall and soil column leaching experiments were conducted to explore the risks and factors influencing Cd loss in surface runoff and underground leaching water at different ground slopes (6°, 12°, 18°, and 24°), rainfall intensities (30, 60, and 90 mm∙h⁻¹), and soil profile conditions. The results show that the risk of soil Cd runoff loss increased at a higher rainfall intensity or Cd pollution degree, reaching a peak at a ground slope of 18°. The main factor affecting soil Cd runoff loss was rainfall intensity followed by Cd soil pollution degree and slope. The risk of soil Cd leaching loss was mainly determined by the leaching time and soil depth. The primary factor affecting soil Cd leaching loss was leaching time, followed by soil depth. The soil organic matter (SOM) concentration and pH minimally affected soil Cd loss. The research results provide a theoretical basis for risk management and control of cadmium loss in contaminated soil, and indicate that the environment-friendly water treatment method of high concentration Cd polluted runoff deserves attention.

To improve the utilisation of mushroom residue waste resources and identify a replaceable matrix material for peat, 10 different formula substrates and three commercially available substrates were examined to determine their physiochemical properties. Furthermore, the correlation and influence of these physicochemical properties on the substrates were explored. Pot experiments were conducted using Brassica campestris L. ssp. chinensis Makino var. communis Tsen et Lee (cabbage), Brassica chinensis L. (pakchoi), Cucumis sativus L. (cucumber), and Cucurbita moschata Duch. ex-Poiret (pumpkin). The results showed that the matrix was most significantly affected by water-holding porosity, aeration porosity, air-water ratio, total porosity, pH, electrical conductivity (EC), available phosphorous (AP), and available potassium (AK). The random forest (RFF) model indicated that pH and total nitrogen (TN) had the strongest influence on the plant height and stem diameter of the cabbage. Moreover, pH, water-holding porosity, and total porosity most significantly influenced the plant height, stem diameter, and seedling vigour index. AP and air-water ratio substantially affected the root length and root-to-crown ratio of the cucumbers, while EC, air-water ratio, and AP influenced the stem diameter, root length, and seedling vigour index of the pumpkin most. The biological characteristics of the four vegetables during the pot experiment indicated that the overall effect of the 10 substrates supplemented with perlite and vermiculite was better than in the basic group. Of these, T2 (mushroom waste: sawdust: catalyst: vermiculite = 8:2:5:5) displayed the best result and could be used as an alternative for peat seedling.

Potentially toxic element (PTE) co-contamination in farmland severely threatens global food safety. To identify effective remediation strategies, large-scale field trials were conducted in two karst regions of Southwest China highly co-contaminated with Cd, Pb, As, Cr, and Hg. The efficacy of seven commercial soil amendments (biochar (BC), fused calcium–magnesium phosphate (FCMP), humic acid (HA), potassium humate (KH), oyster shell powder (OS), composite passivator (PA), and quicklime (QL)) on soil physicochemical properties, PTE bioavailability, maize (Zea mays L.) yield, and plant tissue distribution was systematically evaluated. The results indicated that organic amendments, specifically BC, HA, and KH, consistently outperformed inorganic treatments. These organic materials significantly decreased the diethylenetriaminepentaacetic acid (DTPA)-extractable fractions of cationic PTEs (e.g., Cd and Pb decreased by up to 39.5% under KH treatment) without inadvertently mobilizing As, unlike the alkaline inorganic amendments. This reduction in soil bioavailability closely correlated with improved plant performance, leading to maximum increases in root biomass (up to 130% with BC) and grain yield (up to 27.6% with HA). Furthermore, BC and humic substances effectively restricted PTE accumulation in grains (Cd and Pb reduced by up to 42.1%). Tissue distribution analysis revealed a consistently low root-to-stem translocation factor (TF < 0.2), indicating that roots acted as the primary sink for absorbed PTEs. This study indicates that commercial organic amendments support the use of a superior, broad-spectrum strategy for mitigating multi-PTE risks and ensuring safe agricultural utilization in severely co-contaminated areas.