Study On Biodegradability And Mechanical Transplanting Technology Of Rice PLA Biodegradable Tray

The traditional mechanical transplanting usually uses plastic trays,which are made of polyethylene or polyvinyl chloride.It cannot be degraded naturally after being abandoned,and exists in the environment for a long time,and is difficult to recycle.Long-term and extensive use of plastic trays will have a large pollution hazard on paddy environment.In addition,the sowing rate of nursing seedling is generally above 70 g/tray for forming seedling carpet and reducing the unplanted hill percentage,which leads to weak seedlings,excessive basic seedlings in fields,and poor yield representations for hybrid rice.The biodegradable tray is made with bioplastic-polylactic acid（PLA,a kind of material widely used）and designed as bowl-blanket shape and mechanical transplanting with seedling tray,which could provide a new idea to realize mechanical transplanting of hybrid rice under thin sowing model and green production of rice.In this study,the biodegradability of PLA biodegradable tray and the impact on the ecological environment of rice fields were studied.The seedling quality,the characteristics of mechanical transplanting and the yield in different sowing rates and sowing dates were studied,and the theoretical basis for further improvement and promotion of biodegradable tray was provided.Results showed that:1.The change of degree of biodegradation with time conformed to the Richards equation model when biodegradable tray under controlled composting condition(r²=0.99^**).The maximal biodegradation rate was 1.25%/d in 42 d.The final degree of biodegradation reached 75.55%,which conformed to the requirements of ASTM D5338 and GB/T 20197 on biodegradable plastics biodegradability.Under paddy soil condition,the weight loss of biodegradable tray was first linear and fast rising,and the growth rate slowed down in about 80 days.During biodegradation of one year,the biodegradable tray disintegrated completely into small fragments and the weight loss reached 42.86%.2.The content of heavy metals,polycyclic aromatic hydrocarbons and phthalates of biodegradable tray was far below the national standard and the DDTs were not found.There was no effect on the growth and yield of rice,but little influence on soil nutrient,enzyme activity and microbial quantity.And the survival rate of rice at different treatment levels was 100%,and no damage or malformation was observed.3.Nursing seedling with biodegradable tray resulted in significant the emergence rate increase（P<0.05）,and the lower sowing rate,the higher the emergence rate.The emergence rate of Zhongzheyou 8 in 30 g/tray treatment was higher by 20.57 percentage points than that of the carpet seedling tray.The seedlings roots in biodegradable seedling tray treatment were white,stubby,separate and coiled in bowls due to bowl-blanket design and the average root diameter was 8.63%greater than that of the carpet tray.In addition,the root entwining force of seedlings with biodegradable tray was greater than 100 N in all sowing rates treatments,which met the demand of mechanical transplanting4.Because of bowl-shaped precision transplanting with biodegradable tray,the unplanted hill percentage of Zhongzheyou 8 in 30 g/tray treatment declined by 6.67 percentage points compared with carpet seedling tray.The yield t of biodegradable tray treatment were slightly higher than that of carpet seedling tray.According to the performance of nursing seedlings,mechanical transplanting and yield,70g/tray was appropriate sowing date for biodegradable tray.5.The effects of the different seeding dates(July 1^st,July 6^th and July 11^th)on the seedling quality and yield of the double-cropping late rice were studied in Hangzhou,Zhejiang.Wuyou 308 and Yongyou 2640 were used as materials.The result showed that nursing seedling using biodegradable tray in double-cropping late rice was suitable for Just 1^st.This sowing date treatment could realize safe panicle of late rice and ensure seedling quality,which was not at over-optimum age.In terms of yield,there was a large population spikelets on July 1^st treatment,while the high yield and 1000-grain weight were maintained,and the yield was the highest.