| The planting area and yield of Coix lacryma-jobi in Xingren City,Qianxinan Prefecture,Guizhou Province rank first in the country.In recent years,the production of Coix lacryma-jobi has developed rapidly,and continuous cropping is very common,leading to a decline in yield and quality,which seriously restricts the sustainable development of the industry.In order to explore the obstacle effect of continuous cropping of Coix lacryma-jobi,experiments were conducted in Xingren City,Qianxinan Prefecture in 2021-2022,the effects of continuous cropping on agronomic traits,dry matter and nutrient accumulation,yield,quality,soil nutrients,enzyme activity and microbial population changes during the main growth period of Coix lacryma-jobi were studied,and the changes and correlations of soil nutrients,enzyme activity and microbial population in the rhizosphere were clarified.At the same time,combined with indoor biological determination experiments,the effects of Coix lacryma-jobi plant,decomposition products and rhizosphere soil leachate of different continuous cropping years on seed germination and seedling growth were studied.The obstacle effect of continuous cropping of Coix lacryma-jobi and its autotoxicity mechanism were initially explored,providing a theoretical basis for effectively alleviating the obstacle effect of continuous cropping of Coix lacryma-jobi.The main research results are as follows:1.Continuous cropping reduced the contents of available phosphorus,available potassium,alkali-hydrolyzable nitrogen,total phosphorus,total potassium and organic matter in the soil of coix rhizosphere,which made the soil acidified,the total nitrogen nutrient enrichment,the number of microorganisms in the soil decreased significantly,the activities of urease,sucrase and acid phosphatase gradually decreased,and the activity of catalase increased.Among them,the content of available phosphorus and available potassium in soil after 6 years of continuous cropping decreased by 69.11%and 62.68%,the number of bacteria and actinomycetes decreased by 89.04%and39.86%,and the activities of urease,sucrase and acid phosphatase decreased by 60.13%,26.82%and 49.33%.Compared with crop rotation,the total nitrogen content of soil in6 years of continuous cropping was increased by 66.67%,and the activity of catalase was increased by 63.87%,and the difference was significant.The activities of urease,sucrase and acid phosphatase in soil were significantly positively correlated with the number of bacteria and actinomycetes,and were affected by the contents and p H of available potassium,total potassium,available phosphorus,total phosphorus,organic matter,alkaline hydrolyzable nitrogen and p H,while the activity of catalase enzyme was positively correlated with the number of fungi and total nitrogen content.2.Continuous cropping reduced the total root length,total root surface area,average root diameter and total root volume of coix,resulting in a decrease in plant height,stem thickness and group dry matter,nitrogen,phosphorus and potassium nutrient accumulation,resulting in a deterioration in the yield and quality of coix.The dry matter accumulation of coix plants after 4 and 6 years of continuous cropping was low,and the overall growth was the worst,and the dry matter accumulation of coix plants after 4 and 6 years of continuous cropping was only 62.35%and 39.26%of that of crop rotation.For each year of continuous cropping,the weight of 1,000 grains and grains per hole decreased by 3.318g and 18.97g,the setting rate decreased by 1.4%,the yield decreased by 632.276kg/hm~2,and the dry matter accumulation in the population decreased by 16.29t/hm~2.The yield of coix decreased by 44.13%～53.43%after 6 years of continuous cropping,and the content of soluble sugar,lysine and pullulan in coix grains decreased significantly after 6 years of continuous cropping,which decreased by60.91%,27.39%and 29.17%compared with crop rotation,and the difference was significant,and the crude protein and crude fat content showed a trend of rising first and then decreasing but the difference was not significant.The nutrient contents of available potassium,alkali-hydrolyzable nitrogen and total phosphorus,urease and acid phosphatase activities in continuous cropping soil had obvious effects on the root growth of coix,the soil total nitrogen content was significantly negatively correlated with the yield and quality of coix,the content of alkali-hydrolyzable nitrogen was positively correlated with the content of 1,000 grains and crude fat,negatively correlated with the crude protein content,and the content of phosphorus and potassium nutrients and organic matter were positively correlated with the yield and quality of coix.3.The inhibition effect of coix plants and rhizosphere soil water extract with different continuous cropping years on seed germination and seedling growth of coix has a concentration gradient effect,and the higher the concentration,the more obvious the inhibitory effect.At 0.025 g/m L,the comprehensive allelopathic effect index of decaysate and rotational soil water extract on seed germination of coix was positive,while the comprehensive allelopathic effect index of root and stem and leaf water extract and soil water extract for 4 and 6 years of continuous cropping on seed germination and seedling growth was negative.When the concentration of water leachate was 0.05 g/m L,the treatment of each part of the water leachate reduced the protease andα-amylase activities and soluble protein and soluble sugar content of coix seed at the germination stage,and also reduced the plant height,stem thickness,leaf area,plant dry weight,root vitality and photosynthetic capacity of coix seedlings,but increased the enzyme activity of the antioxidant system(SOD,POD,CAT)and the content of major osmoregulatory substances(proline,malondialdehyde),which stimulated the self-regulation ability of plants.When the concentration≥0.1 g/m L,the treatment of water extract significantly inhibited seed germination,significantly reduced the root length and bud length of coix seeds,and significantly reduced the plant height,stem thickness,leaf area,root vitality,photosynthetic capacity and SOD,POD and CAT activities in leaves,while the content of proline and malondialdehyde increased significantly,which finally led to slow growth of coix seedlings.The order of self-toxicity of coix stems and leaves,roots and decaysate water extract on seed germination and seedling growth was as follows:roots>stems and leaves>decay;The longer the continuous cropping period,the more obvious the inhibitory effect of soil water extract on seed germination and seedling growth of coix.In summary,continuous coix cropping led to soil acidification,soil nutrient imbalance,decreased the number of bacteria and actinomycetes in the soil,increased the number of fungi,decreased the activity of soil sucrase,urease and acid phosphatase,and increased the activity of catalase.Continuous cropping also deteriorated the root growth of coix,which in turn affected the growth and development of the upper part of coix,affected the reproductive growth of coix,and the yield of coix decreased with the extension of continuous cropping years 2.When the concentration of water extract in the rhizosphere soil water extract of coix plants and decaysates and rhizosphere of each continuous cropping year was≥0.1 g/m L,the germination,root viability,photosynthetic ability and antioxidant system(SOD,POD,CAT)enzyme activities of coix seedlings were significantly inhibited,and the content of the main osmoregulatory substances proline and malondialdehyde in the cells was increased,resulting in the slow growth of coix seedlings. |
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