Study On Construction And Application Effect Of Variable Nitrogen Application Model Based On SPAD Value In Rice

Nitrogen was one of the most important elements for crop growth,and nitrogen application was the most important management measures for rice planting.It was an important content in the research of rice nitrogen management that how to apply nitrogen reasonably,and not only to ensure the yield but also to reduce the environmental pollution and the resources waste.SPAD chlorophyll meter was an important instrument of real-time nitrogen management and site-specific nitrogen management which can diagnose crop nitrogen nutrition status conveniently,quickly,in time and without loss.But the nitrogen application model based on SPAD value was more belong to threshold model,and often as auxiliary measure of other nitrogen application models.But traditional fertilization technology that once decided the amount of fertilizer before production did not have its advantage.In this study we explored SPAD value distribution characteristics of rice canopy leaves and nitrogen nutrition diagnosis parameters under different nitrogen conditions,and study the relationship between SPAD value secondary index,yield,apparent nitrogen supply of field and nitrogen application rate under different soil fertility conditions through field tests,using Qyou6 and Zhunliangyou527 as material,and SPAD-502 chlorophyll meter as the main instrument.We built a nitrogen application model — leaf value model,and compared and evaluated its application effect using Qyou6 as material.The main results of this study were as follows:(1)SPAD value dynamic change of rice plants was similar to "three black three yellow" change,which could be as a feature of rice varieties.The appearance times of maximum SPAD value and the third “increase or decrease”change were different under different nitrogen application conditions and rice varieties.The ranges of SPAD value dynamic change was different for same rive varieties in different year,but their change trends were close.(2)Leaves SPAD value of two rice varieties increased with nitrogen application rate.There were significant or over significant positive correlation between SPAD value of canopy leaf and nitrogen application rate under multiple measurements in whole growth periods.The order of ability of indication nitrogen nutrition about the four leaves was as follows:L4>L3>L2>L1.There were significant or over significant correlation between many kinds of SPAD value secondary index and nitrogen application rate in fertilizing stage.The fitting relationship between SPADL4×L3/mean value of rice leaf and nitrogen application rate was obvious,which is not affected by time and variety.So SPADL4×L3/meanvalue could be an ideal parameter of the model of variable-rate nitrogen fertilization of rice based on SPAD value.(3)There was over significant curve correlation relationship between yield and apparent nitrogen supply of field under different soil fertility conditions.Data of two years showed that R2 was 0.5523 or 0.7418.The apparent total nitrogen uptake of the highest yield were close in different years,that was 575.27 kg/ha,546.71 kg/ha,respectively.The difference of maximum yield was 1903.14 kg/ha in two years,having an increase of 20.54%,but the difference of apparent total nitrogen uptake was only 28.56 kg/ha,having an decline of 4.96%.(4)Linear relationships between SPADL3?SPADL4?SPADmean?SPADL3×L4/mean and apparent nitrogen supply of field were significant or extremely significant under different soil fertility conditions at joining stage and heading stage in Qyou6.And fitting effect of heading stage was better than that of joining stage.(5)A general expression for leaf value model was Nw=Nz-[Ys-B)÷k-Ng],Nw,Nz,Ys,Ng meant total nitrogen application rate,apparent total nitrogen uptake,SPAD value secondary index,already using manure amount,respectively,and k,b was slope and origin of linear relationship between apparent nitrogen supply of field(Nx)and SPAD value secondary index(Ys),and Nx was sum of apparent nitrogen supply of soil and already using manure amount.Leaf value model could recommend nitrogen rate of panicle fertilizer(Spikelet promoting and developing fertilize)and basic tillering fertilizer of next season at jointing and heading stage,respectively.(6)Application effects of leaf value model in Qyou6 showed that nitrogen application rate was higher than nitrogen requirement,if irrigation water was insufficient and farmland was arid,when leaf value model was used in field.Variable nitrogen application based on leaf value model could reduce yield difference,increase yield,nitrogen agronomic efficiency and nitrogen partial productivity.