Roles Of Nitrogen Application On Seed Yield And Yield Components In Siberian Wildrye

The field experiments were carried out from 2012 to 2016 at Guyuan Farm and Yuershan Farm in Hebei Province and Xihai Town in Qinghai Province to study:(i)the influence of N application and trimming spike on the dry matter and N content of plant different parts,seed weight,and seed setting rate,(ii)Siberian wildrye seed yield predicted modeling based on canopy Normalized Difference Vegetation Index(NDVI),(iii)the development of a critical N dilution curve for seed production,(iv)the effects of N application,N application split,the interaction of N and phosphorus,and different sites on Siberian wildrye seed yield and yield components to analyse the relationship between seed yield and yield components.The results showed as followings:1.A split plot experiment was carried out to determine the leaf,stem,and spike dry weights and N concentration at anthesis and seed physiological maturity stage and to measure the seed weight and seed setting rate at seed physiological maturity and milk stage respectively.The main plots were N level(0,90,180 kg N hm-2)and sub plots were source-sink treatments(half trimmed and unaltered spikes).Stem and spike dry weights were increased,whereas leaf dry weight was decreased between anthesis and maturity.N application significantly increased all plant parts of Siberian wildrye dry weight and seed weight compared with 0 kg N hm-2 application.The half-spike treatment increased seed weight and seed setting rate across all N levels,and stem dry weight accumulation,but there was no significant influence on N translocation.The results of this study indicate that Siberian wildrye seed yield is source limited since seed weight and seed setting rate were increased in the half-spike treatment with N application.Stem dry weight increased after anthesis suggesting that stems were sinks and competed for assimilates with spikes.Therefore,breeding for increased photosynthesis and partitioning of assimilates from stems to spikes may result in increased and more consistent seed yield.2.The experiments were carried out by completely randomized block design with N application treatments(0～225 kg N hm-2)in two successive growing seasons(2014 and 2015).Shoot biomass(t hm-2),nitrogen concentration(percentage of dry matter),and seed yield(kg hn-2)were measured to calculate critical N concentration,development and validation of the critical nitrogen dilution curve(CNDC).The CNDC for Siberian wildrye seed production was developed with the equation Nc = 3.00 W-0.32(determination coefficient 0.97),based on shoot biomass(between 0.9 and 7.1 t hm-2)and its N concentration.According to the independent data set grouped by seed yield,the developed CNDC could adequately identify the situations of N-limiting seed yield and N non-limiting seed yield before and during anthesis stage,the optimum seed yield was reached at around NNI=1.The CNDC developed in this study provides insight to improve N diagnosis and management in Siberian wildrye seed production under rain-fed conditions.3.A randomized completely block design with nitrogen application(0～225 kg N hm-2)was conducted to determine the canopy NDVI values at different stages and the seed yield at maturity.The results showed that the NDVI values in different stages and seed yield increased with the N application,and the model for predicting seed yield based on NDVI values was established.The equation,Y =27.99e4.71x(R2 = 0.96)was for the first seed production year.And the equation,Y = 11.32e0.90x(R2 =0.90),was for for the remained seed production years,where Y was the seed yield and x was the NDVI value.The validation with independent dataset showed that the determination coefficients of the two regression models based on measured and predicted seed yield were all above 0.98.4.Field experiments using different N application(0～225 kg N hm-2)were conducted at Yuershan Farm and Xihai Town to determine the Siberian wildrye seed yield and yield components.The mean temperature and precipitation during growing seasons in Yuershan Farm were higher than that in Xihai Town,while the seed yield in Xihai Town were higher than that in Yuershan Farm.There was no significant difference in yield components between two sites except for the seed number per spikelet.5.A randomized complete block design was conducted to determine the response of seed yield and yield components to N application split between spring and autumn.N application in spring and autumn both increased Siberian wildrye seed yield and yield components.Compared with N application in spring,N application in autumn significantly increased fertile tillers m-2.At 60 kg N hm-2 application,compared with application in spring,application split between autumn and spring significantly increased fertile tillers m-2,florets per spikelet,and seeds per spikelet,which were not different with application in autumn.In addition,seed yield in application spilt between spring and autumn was significantly higher than application only in spring or in autumn.There was no difference between application split and application in spring or autumn when N application was at or over 90 kg N hm-2.6.Based on the results from experiments above and experiment conducted in Guyuan Farm,the relationship between Siberian wildrye seed yield and yield components was studied by correlation and path analysis.Both fertile tillers m-2 and seeds per spikelet had significant direct effects on Siberian wildrye seed yield.Our results will allow seed producers,seed production researchers and plant breeders alike to more efficiently increase seed yield.