How Much Nitrogen is Left in Your Fields?

Despite some recent precipitation in some areas, producers in the Lower Loup NRD have experienced unusually dry conditions in recent years. Drought can contribute to leaving fields with considerable nitrogen carryover. This can lead to a buildup of nitrogen in the soil that producers should consider when making decisions about their nitrogen needs. Good sense tells us that when there is nitrogen left in the soil from the previous crop, producers should take credit for it –by using it. With the price of fertilizer these days, it just makes good economic sense to use up that nitrogen before it can contaminate groundwater and surface water sources. 

There are several situations that may cause substantial nitrogen carryover.  Dryland fields often have high carryover of nitrogen because they depend on Mother Nature to provide sufficient moisture for the plant to uptake nutrients.  When soil moisture is low enough to cause depleted yields, nitrogen carryover can be significant. Cornfields, whether irrigated or not, tend to have nitrogen carryover, especially if too much nitrogen fertilizer has been applied.  In terms of plant physiology, corn isn’t a very good scavenger of available nitrogen, so it will tend to leave more nitrogen in the soil than soybeans. 

Soybean plants can fix their own nitrogen but will take advantage of nitrogen that is already present in the soil.  Thus, soybeans tend to leave less nitrogen behind than corn.  But this doesn’t mean that you don’t need soil tests before planting corn in soybean stubble.  Another area where there can be nitrogen carryover is on irrigated acres where the amount of water was inadequate.  Some fields may have seen improper irrigation scheduling or there may have been problems with wells not having enough water to keep up with the crop’s water needs. 

The only way to identify the amount of residual nitrogen in a field is to take soil samples. To qualify for the LLNRD Advanced Soil Sampling Cost-Share program, landowners must have certified irrigated acres and must use an approved soil testing method. The LLNRD would then cost-share up to $55 per soil sample up to eight samples per year for four years. Participating landowners will also be required to conduct 36-inch-deep soil nitrate tests, the cost of which will be covered by the Lower Loup NRD up to $15 per soil sample. 

The funding for this program will be available in the next fiscal year, which begins July 2023. Landowners will be able to sign up at their local NRCS office at a date yet to be determined.  

Soil nitrate tests are inexpensive and are a great tool in determining how much nitrogen needs to be applied.  

The University of Nebraska’s Nutrient Management Suggestions for Corn is available at guide will help you determine the rate of nitrogen that is right for your field. 

Good management decisions regarding nitrogen carryover can reduce fertilizer expense. It can also help prevent contamination of the groundwater and surface water resources of our District and state and reduce the associated health risks that come with such contamination.