Supplying amendments alleviates aluminum toxicity and regulates cadmium accumulation by spinach in strongly acidic soils.

Al toxicity and Cd pollution are key limiting factors for agricultural production in the acidic soils in China. The application of amendments is an effective and promising measure for remediating strongly acidic Cd-contaminated soils. However, the information on applying amendments for alleviating Al toxicity and regulating plant Cd accumulation is still rare. Here, oyster shell (OS), red mud (RM), hydroxyapatite (HAP), and biochar (BC) at 30 g kg-1 were investigated for alleviating Al toxicity and decreasing Cd accumulation in spinach plants. The results showed that four amendments significantly increased soil pH, and reduced soil exchangeable Al3+ and DTPA-Cd, promoted spinach growth (P < 0.05). Al(OH)30 and Al-HA were the main forms of active Al in soil. The BC and OS were more effective to alleviate Al toxicity but significantly (P < 0.05) increased Cd accumulation in spinach. RM and HAP effectively reduced the uptake of Cd by spinach plants as well as alleviated Al toxicity (P < 0.05). Bivariate correlation analysis and the partial least squares path modeling analysis indicated that soil exchangeable Al3+ was the main limiting factor for biomass production. Our study demonstrated that HAP could significantly alleviate Al toxicity, promote spinach growth, and decrease Cd accumulation in strongly acidic Cd-contaminated soils. Besides, OS and BC effectively alleviated soil Al toxicity leading to promoting the growth of spinach. Compared with CK, RM treatment significantly reduced soil Cd bioavailability (61.2%) and decreased Cd concentration and uptake of spinach plants by 90.0% and 50.7%. These results indicated that RM could be used as an efficient amendment in Cd contaminated.

Veterinary antibiotics and estrogen hormones in manures from concentrated animal feedlots and their potential ecological risks.

The spread of pharmaceutically active chemicals (PACs), such as antibiotics and estrogenic hormones from animal manures can pose threats to the ecologic environment. In this work, animal manure samples were collected from 71 concentrated animal feedlots in Northern China and investigated for 24 antibiotics and 4 estrogenic hormones. Results showed that these micropollutants were ubiquitous in manures with the concentration ranges of undetectable (ND)-543,445 µg/kg (mean: 44,568 µg/kg) for antibiotics and ND-249.8 µg/kg (mean: 24.78 µg/kg) for estrogens. There was a significant variation in the amounts of PACs in different animal manures. The amounts of antibiotics in manures had following order: swine (83,177 µg/kg) >chicken (52,932 µg/kg) >beef (37,120 µg/kg) >dairy (305 µg/kg), while the estrogens in dairy (mean: 39.27 µg/kg) and chicken manures (mean: 40.08 µg/kg) were higher than those in beef (2.7 µg/kg) and swine manures (1.8 µg/kg). Based on the estimated farmland application rate of manure, antibiotics and estrogens may cause high ecological risks to terrestrial organisms according to the risk quotient evaluation. Estrogens could pose a relatively higher risk than antibiotics. The toxicological effects of antibiotics and estrogens to the terrestrial environment should receive more intensive study.

Unraveling the characteristics of microplastics in agricultural soils upon long-term organic fertilizer application: A comprehensive study using diversity indices.

Microplastics negatively impact soil health and productivity. Organic fertilizers constitute significant contributors of microplastics in agricultural soils. Nevertheless, comprehensive data on the diversity of microplastics in long-term fertilized soils remain unavailable. In this study, we assessed the presence of microplastics in soils subjected to application of three different organic fertilizers (pig manure, chicken manure, and sludge composts) over 12 years, and evaluated the potential ecological risks posed by microplastic accumulation. The average microplastic abundance in soil was 368.88 ± 207.97 (range: 90-910) items/kg. Microplastic abundance differed among fertilization treatments, with substantial increases of 16.67%, 71.67%, and 61.43% upon low to high application of the three treatments, respectively. Overall, the microplastics predominantly comprised fibers (70.94%) and fragments (25.25%), of which a substantial proportion constituted light-colored microplastics (transparent and white). The size of microplastics was mainly concentrated in the 1-2 mm range (39.96%), with rayon, polypropylene, polyester, and polyethylene being identified as the major types. The risk assessment indices of the three treatments were 229.38, 257.64, and 175.89, respectively, and were all classified as level 4 (high risk). The microplastic diversity integrated index and principal component analysis revealed that microplastics were uniformly distributed throughout the 0-20 cm soil depth consequent to tillage activity. Together, these findings provide a comprehensive assessment of microplastic pollution in long-term fertilized soils and serve as a scientific basis for reducing microplastic contamination in agricultural soils.

Does increasing the organic fertilizer application rate always boost the antibiotic resistance level in agricultural soils?

The amendment of organic fertilizer derived from livestock manure or biosolids is a significant driver of increasing antibiotic resistance in agricultural soils; however, it remains unclear whether increasing organic fertilizer application rates consistently enhances soil antibiotic resistance levels. Herein, we collected soils with long-term amendment with three types of organic fertilizers at four application rates (15, 30, 45, and 60 t/ha/y) and found that the higher the fertilization rate, the higher the antibiotic resistance gene (ARG) abundance. However, when the fertilization rate exceeded 45 t/ha/y, the ARG abundance ceased to significantly increase. Moreover, the soil ARG abundance was positively correlated with total nitrogen (TN) content and bacterial abundance, especially Firmicutes, and negatively affected by pH and bacterial diversity. Soil TN/bacterial abundance and pH/bacterial diversity reached maximum and minimum values at the 45 t/ha/y fertilization rate, respectively. Meanwhile, at this fertilization rate, Firmicutes enrichment peaked. Therefore, an organic fertilization rate of 45 t/ha/y appeared to represent the threshold for soil antibiotic resistance in this study. The underlying mechanism for this threshold was closely related to soil TN, pH, bacterial abundance, and diversity. Taken together, the findings of this study advance the current understanding regarding the soil resistome under different fertilization rates, while also providing novel insights into organic fertilizer management in agricultural practices.

Technical solutions for minimizing wheat grain cadmium: A field study in North China.

The minimization of Cd pollution in wheat is urgently needed in many parts of the world. Thus, the aims of the present study were to evaluate the feasibility of popular technologies (i.e., soil amendment and low-Cd wheat cultivar) at sites with different Cd risk levels (high and low) and to propose a risk-based strategy for safe grain production. At a high-Cd site, wheat variety JM22 yielded significantly lower grain Cd than SX828, regardless of soil amendment (biochar, sepiolite, and microbial agent YZ1). Neither biochar nor sepiolite amendment reduced grain Cd, DTPA-Cd, or bioconcentration factors, possibly due to low dosage. Metagenomic sequencing and quantitative PCR showed that YZ1 colonization had little effect on rhizospheric fungal community structure and could not be sustained through winter. At a low-Cd site, significantly lower grain Cd was observed in JM22, LX99, and JM262, which could be used as low-Cd cultivars in the study area. Interestingly, the grain Cd of JM22 was linearly correlated with soil Cd (R2 = 0.84), which allowed the inference of a soil Cd threshold of 1.55 mg·kg-1, below which JM22 alone was capable of producing safe grain. Cost-benefit analysis also indicated that the use of low-Cd cultivars is promising for pollution control. This study provides viable technical solutions for minimizing the grain Cd of wheat grown in northern China.

[Effects of Continuous Application of Sewage Sludge Compost on Heavy Metals Accumulation and Mobility Characteristics in Soil Profile and on Heavy Metals Uptake of Wheat].

The use of sewage sludge compost(SSC)as fertilizer may cause increased leaching due to its high content of heavy metals and thus pose a threat to groundwater quality. The effect of SSC application on heavy metals leaching in calcareous soils has been studied in field trials, which provides basis for determining heavy metals environmental capacity and preventing metal pollution in farmland soil scientifically. The results indicated that the contents of Cu, Zn elevated obviously with the increase of the age and the dosage of SSC utilization in the topsoil(0-15 cm) under 4-year continuous application of SSC. Under higher levels of the compost treatment, the heavy metals Cu and Zn were found to migrate into the 15-30 cm soil and 60-90 cm soil under the experimental condition. Nevertheless, the majority of Cu and Zn from SSC accumulated in topsoil and the highest accumulation rates could reach 75.3% for Cu and 85.9% for Zn. The contents of Cd, Pb increased significantly in topsoil after 4-year continuous application of SSC, and their increases could reach 57.2%-165.2% for Cd and 13%-34% for Pb compared with CK. At 60-90 cm soil, the contents of Cr, As and Pb were also significantly higher than those in CK treatment. Application of SSC not only caused accumulation of some heavy metals in topsoil but also leached heavy metals located in the subsurface soil down in this experiment. Continuous utilization of SSC increased Zn concentration of wheat grain, and the increase could reach 13.3%-47.9%. For the concentrations of Cr and Pb in wheat grain, the values exceeded the national food and healthy standards value (GB 2762-2012) in part of compost treatments. The cumulative ratio of heavy metals carried out by wheat were all below 10% after 4-year experiment, wheat grain carried much more Cu, Zn out than wheat straw, but it was opposite for Cr, As, Cd, Pb. The cumulative ratio of heavy metals carried by wheat decreased with the increasing level of SSC utilization. The amounts of heavy metals migrated to deeper soil should be considered when determining the environmental capacity of heavy metals in farmland soil.

[Distribution of Phosphorus in Soil Profiles after Continuous Application of Different Fertilizers].

This study clarifies the distribution and migration characteristics of phosphorus in the soil profile and discusses the phosphorus load of farmland after continuous application of different organic fertilizers. The distribution and migration characteristics of phosphorus in soil profiles were studied through a field experiment lasting four consecutive years. The results showed that total phosphorus and Olsen-P are mainly accumulated in the soil surface, and their contents decrease with the deepening of soil depth after the continuous application of different fertilizers. With a four-year application of higher levels of organic fertilizer, the total phosphorus was found to migrate into the 15-30 cm soil layer. Olsen-P was found to migrate into the 60-90 cm soil layer under higher levels of pig manure. The ratio of available phosphorus to total phosphorus in the soil surface increased, and there were significant differences after the application of different amounts of organic fertilizers. The amount of Olsen-P as a proportion of total phosphorus in the soil profile decreased as pig manure treatment > chicken manure treatment > sludge treatment > phosphate fertilizer treatment. After the application of chicken manure, pig manure, sludge, and phosphate fertilizer, the value of Olsen-P in the soil surface increased with an increase in phosphorus input and then remained stable. When applying the same phosphorus onto the soil, the contribution of different organic fertilizers to Olsen-P in the surface soil was quite different. The bioavailability and mobility of phosphorus from pig manure was significantly higher than that of chicken manure, sludge, and phosphate fertilizer.

[Accumulation and Migration Characteristics in Soil Profiles and Bioavailability of Heavy Metals from Livestock Manure].

The long term and high dosage application of livestock manure may result in heavy metal accumulation and migration in the soil, which may endanger food security and affect the top soil heavy metal environmental capacity. Thus, one of the most important tasks for prevention of soil heavy metal pollution is scientific determination of the safe use load of heavy metals in livestock manure. A 4-year field plot experiment was carried out to quantitatively study the accumulation and migration characteristics of heavy metals from pig and chicken manure in soil profiles and the differences of bioavailability. The results showed that the contents of Cu and Cd increased significantly by 43.8%-118.6% and 28.2%-44.9% in topsoil(0-15 cm) after 4-consecutive year application of pig manure, and the contents of Cu, Zn, Cd, Cr, As, Pb also increased by 29.7%-48.5%, 239%-456%, 19.9%-80.8%, 40.4%-163%,11.8%-22.0% and 80.3%~95.0% obviously after application of chicken manure. The accumulation rates of Cu and Zn in topsoil were 76.4%-119% and 14.2%-20.4% with pig manure, 72.1%-88.7% and 63.9%-78.9% with chicken manure. Under a high dosage of pig and chicken manure, Cu and Zn migrated to a deeper soil evidently. Applying 60 t·hm-2 of pig manure after 4-consecutive year, Cu could migrate to 15-30 cm soil layer, Zn migrated to 30-60 cm soil layer with chicken manure. Except topsoil, the contents of Cr, Cd, As, Pb did not significantly increase in other soil layers. 4-year continuous application of chicken manure significantly decreased the contents of Cu and Cd, but increased the contents of Zn and Cr in wheat grain and the content of Zn in wheat straw. Pig manure significantly decreased the content of Zn in wheat grain, but increased As content with 60 t·hm-2, the contents of Cu and As in wheat straw also increased significantly. Besides, the cumulative rate of heavy metals in wheat was no more than 6%, wheat grain carried out more Cu, Zn than straw, but the Cd, Cr, As, Pb were opposite. The cumulative rate of heavy metals in wheat decreased with the increasing application of manure. This research has an important significance in scientific determination of the heavy metal loads of plow layer, ensuring the quality and safety of agricultural production, and providing a scientific basis for the source control of soil heavy metal pollution and the safety production of agricultural goods.

Characteristics of Cd uptake and accumulation in two Cd accumulator oilseed rape species.

Two pot experiments were conducted under greenhouse conditions to investigate the characteristics of Cd uptake and accumulation by two Cd accumulator oilseed rape varieties and one Indian mustard grown on a loamy soil that had been artificially contaminated by different amounts of CdSO4 (0, 20, 40, 60, 80, 100 mg/kg soil). The relationship between shoot Cd uptake of the two oilseed rape cultivars and the soil Cd concentrations could be simulated via quadratic equations. The curve showed that maximum shoot Cd uptake of Indian mustard was 314.7 microg/pot at soil Cd concentration of 87.8 mg/kg, while maximum uptake of the variety Xikou Huazi was 543.3 microg/pot at soil Cd concentration of 69.1 mg/kg and that of the variety Zhongyou Za-1hao was 576.7 microg/pot at soil Cd concentration of 84.0 mg/kg, suggesting that shoot Cd uptake ability of the two Cd accumulator oilseed rapes was significantly higher than that of the Indian mustard. Xikou Huazi had higher phytoremediation potential for Cd contaminated soil. Shoot Cd accumulation ability of the two Cd accumulator oilseed rapes was correspond and Cd was easier translocated to the shoot than hyperaccumulator Indian mustard as comparation plant. Shoot Cd distribution pattern showed consistent and significant reduction from older leaves to younger ones of two oilseed rapes and Indian mustard. Cd uptake by oilseed rapes in growth prophase was higher than that of growth anaphase.