Nitrogen fertilizers are required in large quantities for both corn and wheat. N added to the soil is transformed into several different products. In most Ohio soils Ammonia-N or Ammonium-N is rapidly converted to Nitrate-N with the aid of a group of Nitrosomonas bacteria. This process takes from 2 to 4 weeks when the soil temperature is above 50 degrees.
Due to this rapid conversion of Ammonium-N to Nitrate-N, most of the N utilized by plants is the nitrate form. Corn and wheat can take up either ammonium or nitrate nitrogen.
For Ohio, it has been estimated that 50 percent of applied N is taken up by the plant, 25 percent is incorporated into the soil organic matter (available for future crops) and 25 percent is lost from the soil.
Very little can be done to change the amount of N which is incorporated in soil organic matter. Therefore to improve uptake of applied N, N lost from the soil must be reduced. There are three pathways by which N can be lost from soils. One is AMMONIA VOLATILIZATION. This occurs only when soils have a high pH (greater than 6.5), warm temperatures (greater than 50 degrees F), and the N is in dry soil at or very near the surface. Ammonia volatilization is normally of concern only under reduced tillage production systems. Volatilization is of little or no significance in most Ohio soils.
LEACHING accounts for approximately 20 percent of the N lost. Leaching occurs only to nitrates in most soils. Ammonium-N can leach in soils with extremely low cation exchange capacities such as such as sands.
DENITRIFICATION is the biochemical reduction of nitrates, under saturate conditions, to N gases, N2 or N20, and accounts for approximately 80 percent of the N lost.
Nitrate N is the only form of N which is of major importance in N loss from most soils. Once N is converted to nitrate there is little one can do to reduce losses except improve the drainage of the soil. Another alternative is to reduce the conversion of ammonium N to nitrate N. The only practical way to reduce this conversion is to control the Nitrosomonas bacteria which are required for this reaction to proceed.
There are several chemicals which will kill or control the number of Nitrosomonas bacteria in soils. One is nitrapyrin marketed under the trade name N SERVE (REGISTERED Trademark of Dow Elanco).
Results of selected research trials in Ohio are reported in Table 1. Based on these and results from other Midwestern states the expected yield response from nitrapyrin is summarized in Table 2.
Table 1. Typical Corn Yields in Ohio With and Without Nitrapyrin
| Soil Type and Drainage | N Rate, Time and Source | Corn Yield, bu/A | |
|---|---|---|---|
| Without nitrapyrin | With nitrapyrin | ||
| Hoytville silty Clay Loam (Undrained) | 160 lb/A Fall NH3 | 50 | 45 |
| 160 lb/A Spring NH3 | 84 | 84 | |
| Hoytville silty Clay loam (Surface plus tile) | 160 lb/A Fall NH3 | 110 | 120 |
| 160 lb/A Spring NH3 | 124 | 132 | |
| Brookston silty Clay Loam (Surface plus tile) |
80 lb/A Fall NH3 | 125 | 132 |
| 80 lb/A Spring NH3 | 137 | 146 | |
| 100 lb/A Fall Urea | 111 | 111 | |
| 100 lb/A Spring Urea | 115 | 125 | |
| Crosby silt Loam (Undrained) |
100 lb/A Fall NH3 | 78 | 95 |
| 100 lb/A Spring NH3 | 125 | 132 | |
| 100 lb/A Fall urea | 79 | 81 | |
| 100 lb/A Spring urea | 99 | 117 | |
| Crosby silt Loam (Surface plus tile) |
160 lb/A Fall NH3 | 134 | 146 |
| 160 lb/A Spring NH3 | 150 | 152 | |
Table 2. Probable Corn Yield Response from the use of Nitrapyrin With Added Nitrogen*
| Time of Application | |||
|---|---|---|---|
| Soil Conditions | Fall After Soil Temp is Less than 50F | Early Spring before 4/15 | Late Spring after 4/15 |
| Dark Clay Soils** (without improved drainage) |
N - Not Rec. | Mod*** | Mod |
| Dark Clay Soils (with improved drainage) |
Mod*** | High | Mod |
| Light Loam Soils** (without improved drainage) |
Mod*** | High | High |
| Light Loam Soils (with improved drainage) |
High | Mod | Low |
| *Note that this table indicates "yield response" not total yield which is listed in Table 1. | |||
| **Dark Soils greater than 3% 0.M. Light Soils less than 3% 0.M. | |||
| ***Not the optimum time to apply N. If N is applied OSU recommends the use of an ammonia form of N with a nitrification inhibitor. | |||
Prepared by:
Jay W. Johnson
Extension Agronomist
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