Another major N credit to include in the corn N requirement is the N released when sods are tilled under and/or killed.
Sods of all kinds (e.g. alfalfa, grass, mixes, etc.), when tilled under or killed, will release large amounts of plant available N for up to 3 years after the plowing (see the table, below). The N in the sod residue is mineralized over time by soil microorganisms, thereby making the N available for the next crop in the rotation, for example corn. The table, below, contains average annual N availabilities from four major categories of plowed/killed sods. The amount of N released depends on the percentage of legume in the plowed sod, as well as all of the factors that drive N mineralization and nitrification. The percent legume in the sod is based on your in-field estimate of the proportion of legume plants to non-legumes (i.e. grasses, etc.) in the stand.
How many lbs of N/acre are available to a first year corn field following a sod of 26-50% legume?
Legume in Sod |
Total N Pool |
Year 1* |
Year 2 |
Year 3 |
% |
lbs N/acre |
lbs N/acre |
lbs N/acre |
lbs N/acre |
0 |
150 |
83 |
18 |
8 |
1-25 |
200 |
110 |
24 |
10 |
26-50 |
250 |
138 |
30 |
13 |
50 or more |
300 |
165 |
36 |
15 |
*First year following tilling under and/or killing sod.
To read more on this subject: Nitrogen Guidelines for Field Crops in New York (section 3.2)