How to create a For loop with spplot in R?

Question

I have spatial dataframe with sampling locations and a variaty of variables. I would like to create a spatial plot for every variable in a For loop. I used spplot for this, which is working for a single variable when I remove the loop. I have below a short description of the database and the loop I made so far. How can I construct the For loop so it produces saperate plots for every variable?

class       : SpatialPointsDataFrame 
features    : 47 
extent      : -96.57795, -96.56407, 39.10135, 39.10672  (xmin, xmax, ymin, ymax)
coord. ref. : +init=epsg:4269 +proj=longlat +datum=NAD83 +no_defs +ellps=GRS80 +towgs84=0,0,0 
variables   : 18
names       :    Sample_id,         x,        y, bulk_density, Percentage_SOM, Clay, Silt, Very_fine_sand, fine_sand, medium_sand, stone,      Composite_depth, percentage_water, percentage_roots, Percentage_SOM_20cm, ... 
min values  : KLTER/K20A-1, -96.56407, 39.10135,        550.7,            6.9,  3.9, 66.9,            7.4,       0.0,         0.0,   0.1,             7.3,             16.8,             0.10,              4.2315, ... 
max values  : KLTER/K20A-9, -96.57795, 39.10672,       1031.8,           15.1,  8.5, 85.8,           18.5,       9.0,         5.2,  13.7,            20.0,             30.2,             2.16,             11.2000, ... 

df <- K20A_sp3
for(i in names(df))
{ 
  if(is.numeric(df[3,i])) 
    {
    spplot(df, names(zcol= i),
       scales=list(draw=T),
       cex = 1.4, 
       main="Watershed K20A",
       col.regions=brewer.pal(6, "Oranges"))
       dev.off()
     } 
  } 

Loop with making .png file

 for(i in names(df))
     { 
      if(is.numeric(df[3,i])) 
{
  dev.new()
  mypath  <- file.path("C:", "Users", "Ilona", "Documents", "A master thesis", "7.Rstudio", paste("Point_K20A_", i, ".png", sep=""))
  png(file=mypath)
  print(spplot(df, names(zcol= i),
         scales=list(draw=T),
         cex = 1.4, 
         main= paste("Watershed K20A_", i, sep = ""),
         col.regions=brewer.pal(6, "Oranges")
         sp.layout(K20A_DEM))))
  dev.off()
} 

}

Answer 1

You have probably found an answer for this by now, but adding the answer from an equivalent question.

Bottom line is that one needs to 'print' the plot when in a loop:

for(i in 1:10) {
    png(...)
    print(spplot(...))
    dev.off()
}