Question

why does soil have to be plugged before seeds are sawn

Answer 1

so that it gets sufficient nutrients sometimes manure is added before plugging it helps in proper mixing it with the soil , so that roots can penetrate freely

Answer 2

The  soil  should  be  ploughed  thoroughly  before  sowing  of  the  seed  as  this  helps  the  roots  to  penetrate  deep  into  the  soil.  This  also  brings  the  nutrient- rich  soil  to  the  top.  Another  advantage  of  this  method  is  that   the  particles  of  weeds  will  be  uprooted  completely  from  the  soil.  This  also  helps  in  the  growth  of  benefitial  bacteria.