Effects Of Nitrogen Reduction Combined With Silicon Application On Yield And Nutrient Use Efficiency Of Rice Rotated With Tobacco

Tobacco-rice rotation is an important way to enhance tobacco and rice yield,thus guaranteeing food security and offering extra bonuses for growers in tobacco-producing areas in Fujian and other provinces in Southern China.However,there is growing concern over the overuse of nitrogen fertilizers to increase tobacco yield during the planting season.As a typical silicon-accumulating crop,rice(Oryza sativa L.)absorbs greater amounts of Si than the sums of nitrogen,phosphorus and potassium uptake.Silicon application has widely been reported to enhance crop yield.However,far too little attention has been paid to the potential of silicon application combined with nitrogen reduction,until recently,it is unclear whether this method can be applied to enhance rice rotated with tobacco yield and achieving sustainable development.This study thus seeks to investigate the effect of nitrogen reduction combined with water-soluble siliceous fertilizer on the growth,yield and nutrient use efficiency of rice rotated with tobacco through field trials.This study follows a fractional design,the main area of which encompasses four levels of nitrogen application:no nitrogen application(0Kg/hm~2),a 50%reduction in nitrogen application(75 Kg/hm~2),a 25%reduction in nitrogen application(112.5 Kg/hm~2)and conventional nitrogen application(300 Kg/hm~2);and the sub area of which encompasses two levels of silicon application:no silicon application(0 Kg/hm~2)and silicon application(300 Kg/hm~2).Rice yield and its influencing-factors,soil nutrients,dry matter accumulation,nitrogen and silicon nutrient accumulation at different growth stages were examined.The main results are as follows:(1)On the condition of no silicon application,there are trends that with the increase of nitrogen addition,the height,biomass,effective tillers,panicle number and yield are increased,and these indicators peak at 25%reduction range of nitrogen and then decline.On the condition of silicon application,there are trends that with the increase of nitrogen addition,the height,biomass,filled grains number and yield are increased,and these indicators peak at 50%reduction of nitrogen and then decline.Silicon application can significantly increase the height and biomass of rice rotated with tobacco when the nitrogen reduction range reaches 50%or nitrogen fertilizer isn’t applied.The yield increment is attributable to the beneficial effects of Si including the increase of effective panicle number,setting rate and thousand grain weight.In each nitrogen level,silicon application increased rice rotated with tobacco yield by 9.2%(p<0.01),7.3%(p<0.01),2.3%(p=0.214)and 3.4%(p=0.027),respectively.The greatest yield was achieved with a 50%reduction in nitrogen combined with the application of Si,reaching 578 Kg/mu.(2)From the result of biomass accumulation and tillering dynamics,it is shown that silicon application can optimize biomass accumulation and tillering by accelerating the tillering of rice when the reduction range of nitrogen reaches 50%or nitrogen fertilizer isn’t applied.However,when the reduction range of nitrogen is less than 25%,there is no significant effect of Si application.(3)When the nitrogen reduction range reaches 50%or nitrogen isn’t used,applying Si can significantly increase nitrogen content and accumulation throughout growth.However,when the conventional amount of nitrogen is used,Si application would decrease nitrogen content and accumulation.With or without Si application,nitrogen utilization efficiency decreased with increased nitrogen addition,meanwhile,Si application can increase significantly the nitrogen use efficiency in the group of 50%reduction in nitrogen and conventional nitrogen application.(4)In each nitrogen level,Si application can increase significantly the silicon content and accumulation of rice rotated with tobacco.Silicon use efficiency declined with the increase of nitrogen addition,reaches the lowest point in the group of 25%reduction in nitrogen,and then increased slightly in the group of conventional nitrogen application.(5)Silicon application can significantly increase the effective silicon content in the soils;the alkaline nitrogen and total nitrogen content increase as the addition of nitrogen increases.Silicon application increased the alkaline nitrogen content when the decrease range of nitrogen amount reached 25%or above at the tillering stage,but significantly reduced the content of alkaline nitrogen in the ear pumping stage in the group without nitrogen application and 50%reduction nitrogen.At the harvest stage,silicon application significantly reduced the content of alkaline nitrogen in the group of no nitrogen application and 50%reduction nitrogen.Silicon application significantly reduced the total nitrogen content in soils in the group of no nitrogen application,50%nitrogen reduction and 25%nitrogen reduction,at the ear pumping stage in the group of no nitrogen application and 50%nitrogen reduction,and at the mature stage in the group of no nitrogen application.In conclusion,overuse of nitrogen fertilizer remains a problem in rice rotated with tobacco,compared to conventional nitrogen application,reducing 50%nitrogen combined with the silicon application can produce a higher grain yield while saving the input of nitrogen fertilizer.The effect of silicon is significant in stimulating nitrogen uptake in rice and nitrogen release in soils so as to optimize tillage and biomass accumulation and enhance rice rotated with tobacco yield by increasing the number of effective tillers,seed setting rate and thousand grain weight.Moreover,silicon application can also inhibit nitrogen uptake when nitrogen fertilizer is in excess and increase the yield.This study gives a theoretical account and the practical reason for the widespread use of the technique of nitrogen reduction combined with silicon application,thereby enhancing the yield of rice rotated with tobacco and realizing sustainable development.