Soil testing is going strong on harvested wheat fields in many areas and other areas are struggling to get the crop harvested with wet soil conditions. The early trends in soil nitrate levels following wheat production are a reflection of crop yields, N rate applied, rainfall, summer temperatures and many other factors.
Weather each season is a big reason why the amount of nitrate-N left in the soil profile changes from field to field and year to year. Early this spring many areas started out very dry at seeding time (early forecasts were for drought conditions like 1988!). Once we got to June, some areas started getting normal rainfall amounts and other areas received way too much precipitation the rest of the growing season. The result has been variable crops yields within short distances due to isolated storms. This year was also one with hail damage occurring in many areas. In some situations the hail came early and destroyed the crop and there will likely be more nitrate left in the soil profile because the crop did not use it. If the hail came later in the season, most of the N had already been taken up by the crop and the soil nitrate levels will be normal even though the crop was destroyed by hail.
The table below shows the percentage of soil samples that fall into each nitrate range from the first 10,000 wheat fields tested so far this fall. This data gives you a general idea of how variable the nitrogen level is from field to field in this region. As you can see in the table, soil testing is the only way you can determine how much N is left in the soil profile in each field or zone within each field so you can determine how much N fertilizer to apply for next year’s crop.