Text: Bread Clip Knowledge
Edit|Bread Clip Knowledge
«——【Preamble】】 ——»
Yam, also known as dioscines, dioscaceae, perennial root-growing creeping plants, yam contains polysaccharides, flavonoids, diosgenins, a variety of proteins and other components.
The mainland has a long history of yam cultivation and a wide variety of varieties. In the long-term cultivation process in various places, due to environmental and artificial selection and other reasons, a series of characteristic local varieties have gradually been formed.
For example, Guizhou Anshun has cultivated yam for nearly 400 years, and the local provenance cultivated in the region has formed a local characteristic variety "Anshun Yam", which has short roots and stems, thick flesh, solid quality, long-cooked non-stick soup, soft and glutinous entrance, and has extremely high edible and medicinal value.
Soil is the basic measure to maintain productivity and ensure the good growth of plants in agricultural production, and its physical and chemical properties will directly affect the yield and quality of medicinal materials.
«——【Mineral elements in the soil not only affect plants】——»
The physiological and metabolic activities and root nutrition are also the effective nutrients or constituent factors of medicinal and edible homologous plants.
As a tuber crop, the growth and quality of yam are deeply affected by the soil environment.
According to the requirements of GB/T19630 organic product standard and other agricultural regulations and principles, the high-quality production and cultivation of yam have strict regulations on soil environmental conditions, growth technology, and fertilization types.
In recent years, due to long-term continuous planting, the use of a large number of chemical fertilizers and pesticides, and industrial pollution, soil compaction, fertility decline, harmful microbial invasion, heavy metal pollution and other phenomena have been serious, resulting in the inability to increase the yield of Anshun yam and reduce the quality.
Heavy metals pose a huge toxic threat to plant growth and development and human health, and soil heavy metal pollution is an important factor restricting food and drug safety and the development of ecological agriculture, and is one of the most serious ecological and environmental problems.
At present, the measures for the treatment of heavy metals in soil mainly include physical remediation, chemical remediation and biological remediation.
China is the world's largest producer of edible fungi, accounting for 75% of global edible mushroom production. Although the production of edible fungi has important economic value to people all over the world, it produces 5~2.14 million tons of fungus residue every year, which brings waste disposal problems and causes trouble to the environment.
Composting is an environmentally friendly technology, which uses bacterial residue as raw material to compost with lignite to produce high-value organic fertilizer, which avoids environmental pollution and resource waste in the process of discarding and incinerating bacterial residue, and has positive significance for the ecological environment and the utilization of agricultural resources.
In addition, many studies have shown that the organic fertilizer of traditional Chinese medicine compound preparation is rich in nutrients such as cellulose, protein, trace elements, etc., and also has the unique active ingredients of traditional Chinese medicine, which has the effect of disease resistance and sterilization, and has significant effects in soil improvement, pest control, quality improvement, etc.
Moreover, the abundant organic matter and beneficial microorganisms can also reduce the bioavailability of heavy metal ions in the soil by adsorbing and fixing them, thereby reducing the bioaccumulation of heavy metals in crops, which is an important fertilizer type for the sustainable development of agriculture and green organic planting.
However, the study also pointed out that the problem of excessive heavy metals in organic fertilizer is more serious, and can activate the activity of heavy metals in the soil, which is closely related to the raw materials of organic fertilizer, in 2018, a place in the western United States carried out organic fertilizer product quality supervision and spot checks, and the result was 79.3%, and the local government also ordered the company to recall the substandard products and rectify them within a time limit.
Although the long-term application of organic fertilizers such as pig manure significantly improved the soil chemical properties, the contents of available Cu, Zn, Cr, Cd, As and Fe in the soil were significantly increased. Moreover, the application of organic fertilizer lowered the pH of the soil.
While activating soil nutrients, it will also affect the morphology of soil heavy metals and change the bioavailability of heavy metals.
Therefore, the raw materials, methods, and test conditions for the preparation of bio-organic fertilizer are different, and the effects on heavy metals are different. The effects of organic fertilizer raw materials on the composition of organic fertilizers, the effects of the application of various types of biological organic fertilizers on the changes of soil heavy metal content, bioavailability and the effects on the accumulation of heavy metals in plants are still worthy of attention.
Using fungus residue and plant-derived Chinese herbal medicine as raw materials, adding minerals such as phosphogypsum and lignite ash, the fermentation method of active amino acids is used to make fermentation fertilizer of fungus residue and functional fertilizer of active amino acids.
Large-scale fertilization experiments were carried out in Anshun yam planting base to analyze the variation characteristics of heavy metals in soil and plants in Anshun yam at different growth stages under different fertilization treatments.
The effects of two kinds of organic fertilizers alone and chemical fertilizer on heavy metals in soil and yam tubers provide a scientific theoretical basis for the clean planting of Anshun yam and the safe development of bio-organic fertilizer.
«——【Materials and Methods·】——»
This experiment was carried out in Anshun yam planting base in Baotun New Village, Daxiqiao Town, Xixiu District, Anshun City, located at 106°14′62"E, 26°33′80"N, which belongs to the low hilly area, with more flat terrain distribution, deep and soft soil layer, acidic yellow soil, and rich soil nutrient content (Table 1).
Most areas are suitable for the growth of yams, farmers plant yams for a long time, and a certain scale has been formed in the area, with a total production scale of 15,000 mu and a total annual output of more than 30,000 tons.
Functional fertilizer: 40% active humic acid, 40% functional fertilizer matrix, 20% phosphogypsum, proportional mixture, stirring, natural stacking and fermentation for 10~15 days, crushed and granulated after drying, applied as base fertilizer. The preparation method of active humic acid and functional medicinal fertilizer matrix is referred to the patent
"A method for preparing functional medicinal fertilizers by fermentation of active humic acid".
Mushroom residue fermentation fertilizer: the use of mushroom sticks including shiitake mushrooms, oyster mushrooms, lion's mane mushrooms, Ganoderma lucidum, black fungus and other medicinal edible mushroom bran planting and cultivation mushroom sticks, crushed according to the solid-liquid ratio of 1:10, add cellulase, pectinase agent and koji for fermentation for 15 days, separate solid matter and dry, crush and granulation as base fertilizer.
The compound fertilizer is 18-18-18 compound fertilizer, that is, 100kg of fertilizer contains 18kg of nitrogen, 18kg of phosphorus pentoxide and 18kg of potassium oxide, and the ratio of nitrogen, phosphorus and potassium is 1:1:1. The experimental yam species was Anshun yam.
As shown in Table 2, a random block design was used to conduct field experiments, with a total of 5 treatments (Table 2) and 3 replicates in parallel for each treatment, with a total of 15 plots and 30 m2 per plot.
Organic fertilizer and compound fertilizer are mixed in proportion before application and then applied. Basal fertilizer (150kg/plot) was applied to each treatment during yam planting, and topdressing was carried out twice at the early stage of yam tuber expansion (60kg/plot) and late stage of swelling (90kg/plot).
The total dosage of each plot is 300kg. The content of heavy metals in fermented fertilizers, functional fertilizers and compound fertilizers is shown in Table 3.
The soil in the 15 cm tillage layer in the root zone was collected at an indirect equal time before fertilization and after top dressing until harvesting. Avoid fertilization points when sampling.
The sample points were evenly distributed in each cell, and 3 sample points were collected, and a total of 45 sample points were collected in 15 plots. Wooden utensils are used to avoid heavy metal residues during sampling, and samples are taken back to the laboratory for ventilation and drying immediately after collection.
The heavy metal enrichment coefficient (BCF) and the transfer coefficient (BTF) of heavy metals in each organ were calculated as follows:
According to the pollution indexes of potatoes and tuber vegetables, Cr, Cd, Pb, Hg and As were selected as the evaluation indexes of heavy metal pollution of yam (Table 4).
The single factor index and N.L.Nemerow composite index method were used to evaluate the heavy metal pollution in soil and yam as follows:
In Eq. (4), Pi is the single pollution index of heavy metal i, when Pi > 1, it is pollution, and Ci is the average value of heavy metal i; Si is the standard limit value for heavy metal i (Table 4).
There is the square of the maximum value in the heavy metal single factor pollution index; (Pi)2ave is the square of the average of the individual contamination factors in all the heavy metals in the sample.
The specific method of grading is carried out with reference to the national agricultural industry standard "Technical Specification for Monitoring Farmland Soil Environmental Quality" (NY/T395-2012), and the evaluation grades are shown in Table 5.
In this method, RfD is based on the safety limits set by the US Environmental Protection Agency and the tentative tolerable intakes of the World Health Organization (Table 6).
«——【Results and Analysis·】——»
The pH value was the main factor influencing the change characteristics of heavy metal content, and the soil pH decreased significantly at the expansion stage of Anshun yam tubers under different treatment measures, and increased again at the harvest stage, among which the 70% functional fertilizer + 30% compound fertilizer treatment group (GYF) had the largest change range, and the non-fertilization control group (CK) had the smallest change range (Table 7).
Soil organic matter (SOM) content was significantly increased by different fertilization treatments, and the SOM content of the functional fertilizer treatment group (GY) group increased the most significantly (Table 7).
When the pollutants exceed the screening value of soil pollution risk, there may be risks to the quality and safety of Anshun yams, plant growth and soil ecological environment, and the monitoring of the soil environment and the coordinated monitoring of yam products shall be strengthened, and safety and interest measures shall be taken.
Samples were collected from the stems and leaves (II.-y), underground rhizomes (II.-g) and rhizomes (III.-g) at the harvest stage of yam at the tuber expansion stage to analyze the changes of heavy metal content.
The heavy metal content of yam under different fertilization treatments was different in different growth stages and different parts, and the single factor pollution index method (Pi) of yam roots except for CK and GYF treatments at the expansion stage could measure the pollution degree of each heavy metal factor and the contribution degree to the comprehensive pollution, as can be seen from Table 8.
Because of its rich nutrients and active ingredients, yam is a widely loved medicinal and edible homologous ingredient, and yam rhizome is its medicinal edible.
Therefore, the health risk of six heavy metals in the tubers of harvested Anshun yam was evaluated by oral route, and there was no relevant limit standard for Ni in vegetables, so it was not evaluated here.
It can be seen from Table 9 that the single factor hazard quotient and comprehensive hazard index of the six heavy metals in the tubers of Anshun yam under different fertilization treatments were less than 1, and there was no non-carcinogenic health risk.
Among them, the heavy metals Pb, Cd, Cr and As are carcinogenic heavy metals, and it can be seen from Table 10 that the carcinogenic risk index CRisk of four heavy metals in yam tubers under different treatments is CRisk.
In adults, the CRisk was 2.23×10–9~1.79×10–6, and in children, the CRisk was 2.34×10–9~1.88×10–6. The TCRisk of adults and children was 2.55×10–9~4.42×10–6, and the CRisk index and TCRisk index were both lower than 1×10–4, indicating no carcinogenic risk.
The transport coefficient indicates the ability of heavy metals to transfer from rhizomes to shoots, and it can be seen from Table 11 that the transport capacity of yam to different heavy metals is different during the tuber expansion stage.
On the whole, the average transfer coefficients of the seven heavy metals and different fertilization measures improved the comprehensive transport capacity of yam to heavy metals, and continuously transported heavy metals from rhizomes to shoots, which may be the reason for the decrease of heavy metal content in yam rhizomes during the expansion stage.
The effects of each fertilization treatment on heavy metals in soil and yam were comprehensively evaluated by factor analysis, and the scores were shown in Table 12, and the higher the score, the more obvious the effect of the treatment on the increase of heavy metals. Different fertilization treatments had different effects on heavy metals in soil and yam.
In the soil, the comprehensive scores of GYF treatment were the highest in both swelling and harvest stages, which were significantly higher than those of control and other treatments, indicating that the combined application of GYF (functional fertilizer + compound fertilizer) had the greatest impact on soil heavy metal pollution, and GY and JZ were lower than CK at both swelling and harvest stages.
«——【Discussion·】——»
In recent years, the research on organic fertilizer has developed rapidly, and all kinds of resource wastes have been recycled. A large amount of biochar is produced after the fermentation of waste fungus sticks, which is conducive to improving soil structure, passivating and remediating soil heavy metal pollution.
The mainland is a big country of herbal Chinese medicine, and the research and development of plant-derived Chinese herbal medicines as compost raw materials for organic fertilizers is also a research hotspot in recent years.
Phosphogypsum is an associated by-product of phosphate rock production, and there is a large amount of phosphate rock industry and phosphogypsum waste in Guizhou.
Recycling has always been a problem that needs to be solved urgently. In recent years, due to its rich calcium, silicon, phosphorus and other mineral elements, it has been used as a soil conditioner and improver in agriculture, but the utilization rate of phosphogypsum is still low.
Therefore, whether it is a single application of organic fertilizer or a combination of organic and inorganic fertilizers, it is necessary to consider the ecological benefits and environmental carrying capacity in long-term agricultural production to avoid causing environmental and food safety.
At the same time of developing organic fertilizer, we should increase the separation technology of heavy metals from organic fertilizer, and develop green, clean and effective comprehensive functional organic fertilizer from the perspective of green, scientific and sustainable.
Fundamentally solve the problem of soil heavy metal pollution, maintain the stability of soil biological system, and ensure the clean production and safety of agricultural products in today's modern agriculture.