[R-sig-ME] lmer to estimate batch variability

[array chip]

Dear all, I have this simple dataset to measure the yeild of a crop collected in 2 batches (https://drive.google.com/file/d/1lgVZVLHeecp9a_sFxEPeg6353O-qXZhM/view). when I ran a simple inear mixed model using lmer to estimate within-batch and between-batch variability, the between-batch variability is 0. The run showed that data is singular. Does anyone know why the data is singular and what's the reason for 0 variability? is it because the dataset only has 2 batches?
> daty<-read.table("datx.txt",sep='\t',header=T,row.names=NULL)
> library(lme4)> lmer(yield~1+(1|batch),daty)boundary (singular) fit: see ?isSingularLinear mixed model fit by REML ['lmerMod']Formula: yield ~ 1 + (1 | batch)   Data: datyREML criterion at convergence: 115.6358Random effects: Groups   Name        Std.Dev. batch    (Intercept) 0.000    Residual             2.789   Number of obs: 24, groups:  batch, 2Fixed Effects:(Intercept)        5.788  
Thanks!John

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