The Non-destructive Diagnosis Of Corn Nitrogen Status And The Effects Of Soil Moisture And Nitrogen Supply On Corn

Excessive nitrogen （N） application and water deficit are the major global problems. Theyare the foundation of crop growth and development and become the main factors on limitingagricultural sustainable development. Therefor, the reasonable management of irrigation andfertilizer application is the key to achieve energy conservation and emission reduction inagriculture. In current study, the SPAD-502chlorophyll meter, Dualex-3polyphenol meter,Dualex-4N balance index meter, and Multiplex fluorescence meter were emplyed to assesssthe plant N status in maize （Zea mays L.）. The effects of different soil moisture and nitrogenapplication rates on SPAD, Dualex, Multiplex’s parameters readings and their N sufficiencyindex [NSI] of the latest fully leaf were investigated. According to three criterions includinghighly strong relationships with applied N rates, independence from soil water content, andconsistency among growing stages, the corn optimal N diagnosis indicator was selected.Furthmore, the relationships between N assessment indicators, on the one hand, and grain yield,grain NO3-N content, and soil NO3-N content, on the other hand, were analysised. Moreover,the responses of corn leaf phtosyntheis, grain yield, and the soil NO3-N content in differentlays to different soil moisture and N application rates have been studied. It got the mainfindings as follows:1. The N assessment indicator values of the uppermost fully expanded leaves in cornplants, on the one hand, and plant biomass, tissue N content, and plant N nutrition index （NNI）,one the other hand, were highly significant. Compared among N assessment indicators,1/NSIDualex, BGF_G, RF_G, RF_R, NSI_RF_G, NSI_RF_R, and NSI_BGF_UVwere notsuitable to assess N status in corn.2. According to three criterions including highly strong relationships with applied Nrates, independence from soil water content, and consistency among growing stages,NSISPAD/Dualex, NSI_NBI_Dualex-4, RF_UV, FRF_UV, NSI_RF_UV, NSI_FRF_UV,NSI_NBI_G, and NSI_NBI_R were up to criterions, howerver, the range of RF_UV andRF_UV under different N application rates were less than other N assessment indicators, andNSI_RF_UV and NSI_FRF_UV were bad for predicting grain yield. Therefor, NSISPAD/Dualex,NSI_NBI_Dualex-4, NSI_NBI_G, and NSI_NBI_R were optimal N status diagnosis indicators in cuurent study. Furthermore, the grain yield could achieved the maximum vales as the cornoptimal N diagnosis indicators were reach to0.94-0.98during V5-VT growth stages.3. The significant linear or non-linear correlation between SPAD, Dualex, SPAD/Dualex,NSISPAD,1/NSIDualex, and NSISPAD/Dualexreadings, one the one hand, and grain yield, grainNO3-N content, and soil NO3-N content, one the other hand, were observed. Compared amongN assessment indicators, Dualex, SPAD/Dualex, and NSISPAD/Dualexreadings could predictepreferably grain yield; Dualex and SPAD/Dualex readings could predicte preferably grainNO3-N content; and SPAD/Dualex readings could predicte preferably soil NO3-N content.Among Multiplex’s parameters, SFR_G, FLAV, NBI_G, NBI_R, NSI_SFR_G,1/NSI_BRR_FRF,1/NSI_FLAV, NSI_NBI_G, NSI_NBI_R, and1/NSI_ANTH+1readingscould predicte preferably grain yield in corn.4. The N fertilizer topdressing treatments could improve the PNas it was done beforedrought stress, but resulted in reduction after; and the PNin leaves induced drought stressthrough rewatering recovered rapidly and even was higher than rich-watered control. Itindicated that more N supply did not alleviate the effects of drought but aggravated thephoto-damage. Little significant effects of N rates and SWC levels were existent on Fv′/Fm′. Inthe field experiment, LAI and SPAD×LAI increased gradually with increasing N from0to180kg ha^-1, but decreased as N application rate was higer than180kg ha^-1. It indicates thatexcessive (250kg ha^-1) or less (0-60kg ha^-1) N application rates could decreased the LAI andSPAD×LAI process at the end of corn growth stages and the leaf became aged in advance.PN×LAI increased progressively with N rates. The correlation between PN×LAI and corn grainyield was extremly significant, indicating that the improvement of the canopy photosynthesis isthe key to increase grain yield, but there was little value for increasing grain yield as Napplication rates was higher than180kg ha^-1.5. Soil NO3-N contents increased with increasing N ferilization rates, but decreased withincreasing the depth of soil layer regardless of N ferilization rates. With increasing soil watercontents, soil NO3-N contents increased in0-30cm soil layer and had a little change in30-60cm soil layer. After harvest, soil residual NO3-N contents increased with N fertilization rates orsoil water contents. Soil residual quantity of NO3-N was highest in0-60cm soil layer whentotal N fertilization rate was below140kg ha^-1and was highest in60-90cm soil layer whentotal N fertilization rate was below180kg ha^-1.