Research On The Effect Of Silicon Supply On Synergistic Reduction Technology Of Pesticide And Fertilizer In Double-Cropping Areas Of The Middle And Lower Reaches Of Yangtze River

Double-cropping areas of the middle and lower reaches of Yangtze River is the largest main rice growing region of China,which rice production capacity is very important for rice production and food security of China.As a silicon-liking crop,dozens of studies have proved that rice growth,nutrient uptake by rice and resistance of rice to biological and abiotic stresses effectively promoted with Si?silicon?supply,and addition of organosilicon additives can effectively improve herbicidal efficiency of herbicides,which means Si supply has a certain potential to improve the efficiency of fertilizer and pesticide application in rice production process.However,to date there is no reprots have been reported,which systemically studied the Si application potential and mechanism of synergistic reduction technology of pesticide and fertilizer in double-cropping areas of the middle and lower reaches of Yangtze River.Accordingly,a series of field experiments were conducted in the rice planting system of double-cropping in the middle and lower reaches of the Yangtze River.Combined with greenhouse hydroponics experiments,this study systemically analysed the Si application potential and mechanism of synergistic reduction technology of pesticide and fertilizer in double-cropping areas of the middle and lower reaches of Yangtze River,and provides theoretical basis and technical guidance for reducing the input of chemical fertilizers and pesticides in the rice production process in double-cropping areas of the middle and lower reaches of the Yangtze River.The main findings are as follows:1)Appropriate Si supply could significantly improve utilization rate of fertilizer and rice yield.Within the five gradients of Si application rates set in the experiment,the utilization rates of nitrogen?N?and phosphorus?P?fertilizer and rice yield increased first and then decreased with the increase of Si supply.When the the application of SiO₂ was 23.40 kg hm^-2,the utilization rates of N,P and rice yield of four groups all reached the peak.In addition,base application 23.40 kg hm^-2 SiO₂ and 137.10 kg hm^-2 N,67.48 kg hm^-2 P-2O₅,80.98 kg hm^-2 K₂O(early rice without any topdressing,late rice topdressing at tillering stage of 11.25 kg hm^-2N,11.25 kg hm^-2 P₂O-5,13.50 kg hm^-2 K₂O)is the best fertilization method for rice in the double-cropping experimental area of the middle and lower reaches of the Yangtze River,which could reduce about 17%of N and P fertilizer input under the premise of significantly improving the utilization rate of N,P fertilizer and ensuring no reduction in yield.2)Appropriate application of Si can effectively improve the availabilities of N,P and the microbial community structure and diversity of soil microorganisms under the relatively low contents of available N and P in soil.Within the five gradients of Si application rates set in the experiment,the mineralization of N,P,the reserve of organic nutrient that was easy to mineralize and the activity of soil microbial,the number of microorganisms and the activity of important metabolic enzymes related to N,P nutrient cycle increased first and then decreased with the increase of SiO₂ supply,and all reached the maximum at the application of 23.40 kg hm^-2 SiO₂.Statistical analysis results show that the in ecological mechanism of Si can effectively increase the utilization rate of fertilizer and thus increase rice yield was due to Si supply significantly increased the total amount of soil microorganisms of paddy soil,the number of microorganisms and the activity of important metabolic enzymes related to N,P nutrient cycle compared to the control,which contributed to the mineralization of N,P and increased the reserve of organic nutrient that was easy to mineralize,making the soil nutrients easy to be absorbed and utilized by rice roots.The results of high-throughput sequencing also showed that appropriate application of Si can effectively improve the abundance and diversity of soil microbial community structure,and increase the number of microorganisms related to the decomposition of soil organic matter and the cycling of soil N,P,which further explain the ecological mechanism of appropriate Si supply could promote soil N,P mineralization and improve the availabilities of N,P.3)Appropriate application of Si could effectively alleviate the severity of rice fungal diseases.The results of field experiments showed that the severity of fungal diseases in rice alleviated first and then aggravated with the increase of silicon application within the five silicon application gradients,and the severity of fungal diseases in rice were the least at the application of 23.40 kg hm'2 SiO₂.The results of hydroponic showed that appropriate concentration of Si treatment could significantly promote the silicification of epidermal cells to form compact silicified cell lines,increase the content and distribution of the cuticle wax of the rice leaves,and significantly increase the content of Si in rice leaves and stems,which depressed the growth of pathogenic fungi mycelium.Thus,the mechanical resistance of rice to the invasion of pathogenic fungi was improved.In addition,appropriate concentration of Si treatment could reduce the content of Malondialdehyde?MDA?and enhance the activity of Peroxidase?POD?,Polyphenol Oxidase?PPO?,Superoxide Dismutase?SOD?,which enhanced the physiological resistance of rice and thus further alleviated the damage of pathogenic fungi to cells.4)Adding appropriate amount of organosilicon additives can obviously improve the efficiency of herbicides and the foliar fertilizer.When the addition volume fraction of organosilicon additive reached the critical micelle concentration?0.05%?,the weed control efficiency of herbicides and the accumulation of zinc?Zn?and manganese?Mn?in leaves were the best.In addition,the addition of organosilicon additives in foliar fertilizer can obviously improve the interfacial properties of fertilizer liquor.The surface tension is negatively correlated with the volume fraction of organosilicon additives in the range of volume fraction of silicone additives added,wetting diameter and spreading area of fertilizer liquor are positively correlated with the volume fraction of organosilicon additives in the range of volume fraction of silicone additives added in the experiment.And the drying time of fertilizer liquor and the maximum retention on rice leaves showed a trend of first increasing and then decreasing with the increase of the volume fraction of organosilicon additives,and reached the peak when the addition volume fraction of organosilicon additive was 0.05%,respectively increased by 25.90%and 88.79%than that of the control.It was concluded that the key mechanism of increasing the application effect of foliar spraying fertilizer and pesticides by adding appropriate volume fraction of the organic silicon additive was that organosilicon additives could improve the interfacial properties of the spray fertilizer and pesticides solution,thus increase their infiltration,spreading and retention time on rice and weed leaves.