Nitrogen carryover unlikely for most of Indiana
Since both NH4 and NO3 are plant available and much of the NH4 may not have been converted to NO3, request the laboratory measure both N forms. Most laboratories will report ppm of NH4‐N, but if ppm NH4 is reported divide by 1.3 to convert NH4 to NH4‐N. Background levels of NH4‐N are typically less than 10 ppm at corn sidedress time.
Nitrogen fertilizer is one of the most expensive and impactful inputs in corn management. Excess applied N reduces profit and negatively impacts the environment. Insufficient N reduces yield and profit.
If you believe carryover N from last year’s drought stricken crop is likely in your fields then soil sampling for NO3 and/or NH4 as a basis for a reduction in this year’s fertilizer application is wise. Otherwise utilizing the general N recommendations (which are based on an average level of background N over the previous 7 years) are warranted. Read the most current Nitrogen Management Guidelines for Indiana.