Can I test my fields for nitrate in early spring, before preplant applications of nitrogen (N)? Many producers who do not want to sidedress their N are asking this question. The question is common because some states recommend testing soils for nitrate at this time. Such recommendations make sense where the amounts of nitrate carried over from one season to the next vary greatly. Great variability in this "residual nitrate" should be expected in fields treated with high rates of fertilizer N for the previous crop. The value of such testing is questionable, however, for corn grown after soybean or alfalfa in Iowa.