| At present,several problems existed in the fertilization process of rice production have been founded.Firstly,over-application of chemical N fertilizers has been a common problem in intensive agricultural regions of China,especially in Jiangsu province.Secondly,higher labour/time costs for split applications of urea-N which used to optimal plant root N uptake and improve NRF and grain yields.In generally,split applications of N fertilizer involves the use of 3-4 top-dressing applications over the entire growth stage,but more frequency times for machine-transplanted rice.Moreover,it is difficult for farmers to apply the right rate and amount of fertilizer by hand,and this can easily lead to over-application.Furthmore,surface fertilization of urea could lead to loss of nitrogen fertilizer and low utilization rate of fertilizer,resulting in environmental problems.Thus,it is crucial to research rice production technology with high yield and high efficiency as well as lower labour/time and fertilizer costs.A single basal application of controlled release nitrogen fertilizers(CRNF)can improve nitrogen use and rice yield,but it is greatly affected by the fertilizer type.Side-dressing placement fertilizer is a special band fertilization technique on machine-transplanted rice.With the continuous development of machine-transplanted rice,this technology has a great prospect.Combining the rice side-dressing placement with controlled release fertilizers have potential to minimize the labor input,but the effect on rice yield,quality,nitrogen absorption,distribution of soil nutrients and nitrogen leaching loss on paddy fields is still lacking.A field experiment was performed in 2015-2016 with three types of CRNF(bulk blending fertilizer(BBF),polymer-coated urea(PCU)and sulphur-coated urea(SCU))with two fertilizer placements(a single basal application with broadcasting(B)and banded-placement fertilizer use by mechanical side-dressing fertilization(S)).Conventional high-yield fertilization(four split applications of urea at 216 kg N ha-1(CK))and 0-N treatments were established as controls.The experiment was conducted at a farm belonging to Nanjing University,Yanling Town of Danyang City,Jiangsu Province,China.In this study,we studied the effects of different CRNF types and fertilization methods on rice yield;the synchronization relationship between temporal and spatial distribution of soil(soil solution)nutrients and nitrogen absorption of rice;as well as the evaluation of nitrogen leaching loss,N budgets and economic benefits from paddy field.Thus,the objective of this study was to derive management options for improving rice yield and N use efficiency of the machine-transplanted rice.The main results were as following:1.Combining controlled-released nitrogen fertilizers and side-dressing placement on plant growth and grain yields formation of blanket-seedling machine-transplanted riceThe rice yield cannot reach the level of conventional high-yield fertilization(CK)using a single basal application of SCU and PCU.In the single basal application of BBF,the tillering was apparently higher than CK in the prophase,and the dynamics of population growth(dry matter accumulation,leaf area index,plant type in heading stage,photosynthetic capacity)were equal to or slightly higher than that of CK in the middle and late stages,and thus led to a similar grain yield to that of CK.Compared with the broadcast fertilizer application,side-dressing fertilization significantly increased the peak seedling,dry matter accumulation in tillering and panicle differentiation periods,and the material production varied with the type of fertilizer after heading.The utilization of SCU on side-dressing placement significantly increased leaf area index at the heading stage,SPAD of flag leaves,net photosynthetic rate,promoted root growth,improved dry matter accumulation at heading and maturity stages,and eventually significantly increased rice yield.There was no significant difference in the yield using side-dressing placement of PCU,mainly due to a significantly lower seed setting rate.The utilization of BBF slightly increased yield,but not significantly.Overall,our results suggest that the side-dressing placement of fertilizers using SCU and BBF serve as a promising alternative to the use of conventional high-yield fertilization method,generating higher rice yields and economic benefits.2.Combining controlled-released nitrogen fertilizers and side-dressing placement on nitrogen uptake and utilization of blanket-seedling machine-transplanted riceThe N release of SCU tended to be "more in the early growth stage,less in the middle and late growth stage",while that of PCU appeared to be "less in the early growth stage,more in the middle and late growth stage".A single basal application of SCU and PCU significantly reduced N uptake and N apparent recovery(NRF)of rice compared with CK.The application of BBF showed more balance on N supply over the whole growth period,and the N uptake was not significantly different to CK at the mature stage.Compared with broadcasting,side-dressing placememnt fertilizer could supply higher NH4+-N concentration in the plant rhizosphere soil during the early growth stage and prolong the duration of N availability;as a result,side-dressing with SCU,PCU and BBF increased plant N uptake by 32.2%,10.7%and 4.3%,respectively.Compared with broadcasting,side-dressing of PCU significantly decreased the N uptake at heading and maturity stages,which might be related to the unreasonable population composition at heading stage.The efficiency of N recovery was higher than CK when using SCU and BBF under side-dressing placement,and the data of BBF reached a significant level after two years.Overall,our results suggest that side-dressing placement serve as a promising alternative to conventional fertilizer used by broadcasting.Side-dressing placement with SCU and BBF obtained higher N uptake and NRF when compared with conventional high-yield fertilization method.3.Combining controlled-released nitrogen fertilizers and side-dressing placement on N leaching and N budgets of blanket-seedling machine-transplanted rice in the Taihu region of ChinaThe variation of NH4+-N concentration in the percolation and surface water varied in distinct patterns for the different CRNF,irrespective of the fertilization placement.NO3--N concentration in the percolation water had a great temporal variability with rice growth in each year,which caused by the water management.Side-dressing placement with CRNF correspondingly increased mineral N concentration(NH4+-N+NO3--N)in the percolation at depths of 20 and 60 cm but reduced them in the surface water compared with broadcast,although the benefits varied depending on the CRNF type and growth stage.Side-dressing placement of SCU and PCU significantly increased N leaching and the mineral N in 40-60 cm soil layer relative to broadcast,due to the intensive N release during tillering and ineffective stage when the rice plant had a weak N uptake capability.Side-dressing of SCU received the highest N leaching by 6.65 kg N ha-1 and 5.34 kg N ha-1 in 2015 and 2016.By contrast,BBF exhibited the lowest N leaching,regardless of fertilization placement,because of the more balanced N supplied throughout the entire rice growth period.Moreover,side-dressing fertilization of BBF showed singficantly lower N apparent losses,and no singficantly increased in N leaching when compared with CK.Overall,taking economic and environmental effects into consideration,we believe that combining CRNF and side-dressing placement is a new potentail fertilization method for CRNF that can effectively replace conventional high-yield fertilization methods of machine-transplanted japonica rice. |
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