Carryover issue is mostly due to low temps and lack of moisture out this way.  In the East, you guys have plenty of rain to help break things down.  We get 20" annual precip including snow here so things tend to "stick" around longer.  The only thing we have going for us is good PH and relatively high OM. Depending on the chemical soil PH and OM can play an important part as well.  Bottom line is it takes something to break the chemical down so if you don't get enough rain or your PH or OM is out of a normal range you have to be really careful.