Main Soil Obstacle Factors Affecting Garlic Growth In Pengzhou

Pengzhou is an important garlic planting area in Sichuan,but there have been serious obstacles in the garlic planting soil recent years,which affected the garlic yield and quality and resulted in huge economic losses to farmers.In this study,soil p H value,soil environmental factors,including nutrient content,Al³⁺concentration etc.,of the garlic planting soil in Pengzhou were determined,and the effect of solution p H on the garlic root growth was verified by hydroponics experiment,and the relationship between soil acidification and garlic growth obstacles was discussed.The main results were as follows:（1）A total of 52 garlic disease soil samples（disease soil）and 37 garlic normal growth soil samples（normal soil）were collected from garlic planting soil at Longfeng Town,Junle Town,Gexianshan Town and Danjingshan Town in Pengzhou.The soil p H value was determined and the results showed that,most of soil had low p H value.Among the 89 soil samples tested,the ratio of highly acidic soil samples（p H<5.5）accounted for 61.80%,and the extreme highly acidic soil samples（p H<4.5）accounted for 11.24%.Of them,in the garlic disease soil,the ratio of highly acidic soil samples（p H<5.5）accounted for78.85%;In normal soil,the ratio of highly acidic soil samples（p H<5.5）accounted for37.83%,which showed that acidification is common in garlic planting soil in Pengzhou.The spatial distribution diagram of soil p H value in the research area was drawn using Arc GIS10.0.The spatial distribution of different p H values of the soils in the study area showed small clumps or bands.The soil in the 0-20cm layer showed significant acidification,and the soil with a p H<5.5 accounted for 30%.The soil p H of 20-40cm layer is between 5.50～8.09,which belongs to neutral soil.（2）Furtherly,the acidification reason of the representative soil samples at Longxing town,Junle town,Gexianshan town and Danjingshan town was analyzed,the results showed that the hydrolysis acid content of disease soil was 16.17%,42.48%and 40.41%more than that of normal soil,respectively;and the exchangeable acid content of disease soil was 147.06%,388.10%and 138.04%more than normal soil,respectively.The ratio of exchangeable Al³⁺accounted exchangeable acid of disease soil was 81.85%,90.26%and82.10%,respectively;the proportion of exchangeable Al³⁺was obviously make the garlic planting soil acidification.The content of water-soluble aluminum in the diseased soil was significantly higher than that of the normal soil at 245%,45%and 71.43%.（3）The total exchangeable salt base in diseased soil was 29.99%,31.22%and 26.58%lower than that in normal soil.The base saturation of diseased soil was 19.56%,15.44%and 13.96%lower than that of normal soil.The decrease of soil base saturation,especially the decrease of exchangeable Ca²⁺content and exchangeable Mg²⁺content directly resulted in the decrease of soil p H.The concentration of main acid ions in diseased soil was 7.56%,30.70%and 29.71%lower than that in normal soil at Longxing town,Junle town,Gexianshan town and Danjingshan town.Soil Cl^-concentration was positively correlated with acidity index.（4）The results of hydroponic experiments showed that the growth potential of garlic seedlings was worse when the p H of culture medium decreased.When the nutrient solution p H≥5.0,the garlic root could grow normally.While the nutrient solution p H≤4.5,the total root length,root surface area and diameter of garlic roots was significantly less than that of p H≥5.0.When nutrient solution p H=4.0,the maximum root length was only 4.2cm and the total root length was only 17.99cm.In a nutrient solution with a p H of 3.5,the base of the garlic rotted and the root could not occur.The root growth status of garlic seedlings was consistent when cultivated in soil extract and Hoagland nutrient solution with the same acidity.After adjusting the p H value of the diseased soil extract to the same p H value of the normal soil extract（p H5.5）,the garlic root could grow normally.In summary,the increase of the active aluminum ions content and lower soil p H,lead to soil acidification,which was the main reason resulting in garlic planting obstacles in Pengzhou.