Effects Of Oyster Shell Soil Conditioner On Soil And The Quality Of Nandao Seedless Litchi

In shellfish processing,edible parts have been effectively processed while the shells are mostly discarded as processing by-products,which seriously pollutes the ecological environment.Therefore,how to increase the additional value of shells and realize the effective usage of resources has become an important research topic of circular economy.According to statistics,acidified soil accounts for more than 40%of total arable land in China and is still increasing.There is an urgent need to find effective way to control soil acidification.In this study,waste oyster shells were calcined at high temperature to prepare soil conditioner and applied to the soil of Nandao seedless litchi.The effects of oyster shell soil conditioner on soil physical and chemical properties and fruit quality were studied and the indicators of Nandao seedless litchi were discussed.This work aims to provide a basis for the utilization of oyster shells as resource and provide effective solutions for controlling soil acidification and improving crop quality.Shells of oyster,mussel,mussel,abalone,clam and scallop were calcined at 600,650,700,750 and 800°C for 30 minutes.The structure,p H value and exchangeable Ca²⁺content of the product was determined.The results show that all six calcined shell products can adjust acidity.However,among the 6 kinds of shells,only oyster shells showed obvious honeycomb-like microporous structure（diameter 2-10μm）after being calcined at 800°C for 30 min,and the exchangeable Ca²⁺content was the highest.Therefore,calcined oyster shells were used for the following work.To study the adsorption effect of oyster shells on heavy metals Cd²⁺and Pb²⁺,commercial oyster shells calcined at 800°C for 30 minwere obtained.Different addition amounts and reaction times on the absorption effect was investigated.The results showed that calcined oyster shells are effective in absorbing Cd²⁺and Pb²⁺andthe effect was in positive correlation with the addition amount.In order to explore the effects of calcined oyster shell powder on the soil acidification and fruit quality of Nandao seedless litchi,four oyster shell powder dosages,including 0 kg/tree（CK）,1 kg/tree（T1）,2 kg/tree（T2）and 3 kg/tree（T3）were used for field experiments,soil p H,bulk density and organic matter content were measured in the 10-month follow-up measurement.By analysis of the soil nutrient content of the Nandao seedless litchi,it is found that the oyster shell soil conditioner can significantly increase the p H value of the soil,reduce the soil bulk density,and significantly promote the absorption and utilization of the effective components of the soil by the litchi.Compared with the control group CK,for the application amount of 1kg/tree,the soil p H increased from 5.09 to 6.13,an increase of 1.04 units,and the bulk density decreased from 1.46±0.06 g/cm³to 1.28±0.05 g/cm³,a decrease of 12.33%.When the application rate was 2 kg/plant,the soil p H value increased from 5.01 to 6.33,an increase of 1.32units,and the bulk density decreased from 1.46±0.06 g/cm³to 1.28±0.02 g/cm³,a decrease of12.33%.When the application rate was 3 kg/plant,the soil p H value increased from 5.08 to 6.27,an increase of 1.19 units and the soil bulk density decreased from 1.46±0.03 g/cm³to 1.26±0.03g/cm³,a decrease of 13.70%.During the whole growth period,the content of soil organic matter,available potassium and available phosphorus that showed a trend of first rising and then falling.After the Nandao seedless litchi fruit matures,the fruit quality indexes such as fruit weight,sugar-to-acid ratio,vitamin C and so on were determined.It was found that the application of soil conditioners is beneficial to improve the fruit quality.Compared with group CK,for the application amount of 1 kg/tree,single fruit weight and fruit hardness increased by 20.79%and52.14%,respectively.Both the sugar-acid ratio and the solid-acid ratio significantly improved.When the application rate was 2 kg/plant,the fruit firmness,sugar-to-acid ratio and polyphenol content were the highest,which were 58.92%,42.32%and 12.5%higher than those of the CK group,respectively.When the application rate was 3 kg/plant,the weight of single fruit,the content of vitamin C and the content of polyphenol oxidase increased by 28.35%,31.86%and23.46%,respectively.After application of oyster shell soil conditioner,the total fruit yield of the experimental base（the area is 3 mu）in 2021 was about 3000 kg,an increase of approximately30%compared with the production in 2020（without application of oyster shell soil conditioner）.In summary,oyster shells calcined at 800°C for 30 min has a good effect of neutralizing acidity,replenishing calcium and adsorbing heavy metals.A soil conditioner based on oyster shells was developed and applied to the acidified soil of Nandao seedless litchi.The soilconditioner can significantly neutralize soil acidification,reduce soil bulk density,promote the absorption and utilization of soil nutrients by the plant,significantly improve fruit quality and increase production.