What is your residual soil nitrate telling you?
Oct 05, 2020
Residual soil nitrate is a valuable measure in soil testing because it reveals the amount of nitrogen left over from the growing season and provides a starting point for nitrogen fertilizer plans for next year’s crop.
Weather is the driving factor for residual nitrogen variability, and with this year’s variable weather, we are seeing a wide range of residual soil nitrate levels this fall. AGVISE Soil Labs has found that soil nitrate levels following wheat in our area, are distributed approximately a third in each of the 0-30, 31-60 and >60 lb/ac ranges (tested to the 0-24 inch depth).
If your residual soil nitrate is less than 30 lb/ac, yield or protein may have taken a hit in the past season’s crop. Low levels of residual soil nitrate may be explained by using lower rates of nitrogen fertilizer, higher crop yields, cool summer temperatures which would reduce nitrogen mineralization, or excess rainfall which could lead to leaching and denitrification. It is important to note that our new high-yielding cereal and oilseed varieties generally require higher nitrogen fertilizer rates to account for their higher yield potential.
If levels are higher than 60 lb/ac, there may have been an over-application of nitrogen fertilizer. High levels of residual soil nitrate may also be explained by lower than expected crop yield, warm summer temperatures which would increase nitrogen mineralization, or reduced nitrogen loss due to drier conditions.
The 31-60 lb/ac residual soil nitrate level is a good equilibrium for post-harvest nitrogen status and a good base to build an effective nitrogen fertility plan for next season. Please consult with your local Shur-Gro agronomist for assistance with your fertilizer strategy.