Dear All,
A theoretical variogram was fitted to empirical semivariogram model on
residual after accounting for the global trend by regressing the response
variable on the spatial coordinates as showed below. This is done for other
model such as exponential, Gaussian, and linear. I intend to carry out
2-fold cross validation through ordinary kriging. I defined model formula
as yield ~1 but no result. If I decide to use yield ~ easting + northing
for the function krige.cv, this is no  longer ordinary kriging but
universal kriging.

Please could anyone guide me on how the ordinary kriging should be carried
out whenever the variogram model is carried out on the residual of linear
model as given below?

## Fit empirical semivariogram

empvar<-variogram(yield~easting + northing, canmod.sp, cutoff=435,
width=30, Cressie=T)
plot(empvar,xlab="Lag distance (m)",ylab="Semivariance")


## Spherical variogram model
sph.var <- vgm(psill = 75, model = "Sph", range = 50, nugget = 260)
sph.mod <- fit.variogram(empvar, model = sph.var)
print(sph.mod)
plot(empvar, model = sph.mod, main = "Spherical variogram model")


#### Cross validation of the variogram models by ordinary kriging
sph.kcv <- krige.cv(yield~1,canmod.sp, model = sph.mod, nfold = 2)

Thanks while looking forward to reading from you.
Moshood

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