I Used Manure; How Much Nitrogen Do I Need for My Corn?

If you use manure, the amount of fertilizer nitrogen you apply at planting affects your pre-sidedress testing options later this spring.
I Used Manure; How Much Nitrogen Do I Need for My Corn? - News


Corn No-tilled into Bedded Pack Manure, Photo: Andrew Frankenfield, Penn State

The use of poultry manure has become much more popular as more chicken houses continue to be built in the region. The manure from many of those houses is typically exported off the farm. Manure can be an economical fertilizer source, but calculating the nitrogen availability can be a challenge. There are a few tools that are available to test corn before a sidedress application of nitrogen is made to determine if additional nitrogen is needed. These testing tools are most effective when there is a history of manure applications and less than 15 pounds per acre of fertilizer nitrogen is used at planting.

The pre-sidedress soil nitrate test (PSNT) for corn is a soil test taken just before sidedressing which determines the nitrate-N available in the soil at that time. The results are then used to make sidedress N recommendations. Research has shown that when the soil nitrate-N level is above 21 ppm, there is little chance of an economic response to adding additional N to the field. At soil nitrate-N levels below 21 ppm, sidedress N will be required to achieve optimum economic yield. Rates of N can be determined by the results of the PSNT and explained in Pre-sidedress Soil Nitrate Test for Corn.

A similar test, called the chlorophyll meter test, is used to estimate the nitrogen status of the growing corn crop based on the color of the corn leaves. This test is also a pre-sidedress test, run at the critical time just before the major demand by the crop. The color of the leaves is read directly on the plant in the field with a handheld meter. Thus, no samples need to be collected and analyzed and the results are available immediately. More information about the test is explained in The Early Season Chlorophyll Meter Test for Corn.

Both of these tests are recommended for use primarily on fields where there are significant organic N contributions, such as a history of manure applications or a use of forage legumes in the crop rotation cycle. These tests have limited value on most fields without organic N contributions, because these fields generally have low N levels and thus the standard recommendations are suitable.

The latest tools measure Normalized Difference Vegetation Index (NDVI) values to determine crop health status, such as GreenSeeker. This technology can be mounted on a sidedressing rig and used to apply variable N rates on the fly. See more information at Cornell's New Technology for Corn Nitrogen Needs.

No matter what tool you use they all recommend applying a high Nitrogen strip to a small area of each of your fields to calibrate the meters against. These nitrogen rich strips will be used as a reference prior to sidedressing. Nitrogen management will continue to be a challenge because of environmental conditions.

The other thing to consider is at the end of the year you can do a late season stalk nitrate test. The Late Season Cornstalk Nitrate Test has been demonstrated to be a reliable end-of-season indicator of crop N status based on research performed throughout PA as well as other states.