The method of water application and the method of nitrogen application also influence the nitrogen fertility program. In rill, border, or other methods of surface flow application, the amount of water penetrating into the soil is proportional to the distance from the turnout point as a contact time and penetration rate function. In order to bring the end of the run up to the desired moisture status the start of the run must receive an excess. This influences the nitrogen fertility level. Sprinkler systems (aside from cost) also have application pattern. An addition of nitrogen through the water may help to lessen the leach-loss problem in both methods but again there are distribution pattern problems which must be considered. Results of good water management together with good nitrogen control can be instrumental in obtaining maximum net dollar return from crops.

Nitrogen Application

The problems of when, how, and what type of nitrogen to apply should also receive some attention. The following consideration should be kept in mind:

1. Nitrogen in the nitrate form is immediately available to plants and should be used in cases where an immediate source of available nitrogen is demanded, especially in low organic matter soils where microbial activity may be limited. Nitrate nitrogen is especially useful for late fall or early spring seedings where the soil is subject to low temperatures. A limiting factor in the use of the nitrate nitrogen form is its susceptibility to loss by leaching from the soil under certain excess moisture conditions.

2. While some plants have the ability to utilize a small amount of ammonium by direct cation exchange in many cases the ammonium nitrogen must be converted by the soil micro-organisms to the nitrate form before utilization by plants. Ammonium nitrogen does have the advantage of being absorbed on the soil colloidal system and thus is less subject to leaching. Ammonium nitrogen can, and should, be applied ahead of the growing season, as it will be held in the soil until nitrification converts it into the more readily usable nitrate form. Late fall or winter application may be of benefit in many areas. If the winter temperatures are sufficiently cold to stop nitrification or if precipitations is low to moderate, leach losses will be minimal.

3. Better field working conditions often exist in the fall in comparison to spring. Timing, equipment, fertilizer, and labor situations may be more favorable in the fall. Crop response field patterns to guide the soil testing are also fresher in mind. These considerations may be sufficient to offset loss considerations.

4. The urea form of nitrogen, although readily soluble in water, is generally not subject to leaching because it is converted to ammonia and as such, held in the soil until nitrification takes place. However the urea form of nitrogen is leachable before the conversion to ammonia takes place.

5. The release of nitrate nitrogen from organic matter does not take place until after the soil has been warmed and then reaches a peak release rate somewhat late in the season. This should be kept in mind when planning a nitrogen fertility program.

Recommedation Rates for Nitrogen

Every crop and variety of crop in any area has slightlydifferent nitrogen needs for the most economic response. Every area and each soil type within anarea will require different amounts of nitrogen per acre for best response for like crops. Farm and soil management, moisture control, weed control, insect and disease control, trash or residue to be plowed under, residual soil fertility, plus many other factors influence recommendation rates. The following example amounts reflect high yield values for unlimitiing moisture, 150+ day growing seasons, and good crop management.

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