Nitrogen is critical in nutrient management for corn production. When nitrogen was cheap through the 1990s, nitrogen management consisted mostly of applying enough for the crop plus some insurance amounts to accommodate wet weather. By the time nitrogen prices reached $.75+ per unit in 2008, nitrogen management by insurance was no longer a good management practice. Increasing environmental concerns about nitrogen losses to ground and navigable waters puts further pressure on nitrogen management.
All forms of nitrogen (anhydrous, urea and liquid) convert to nitrate nitrogen in the soil in the presence of moisture and soil temperatures at or above 55 degrees. Nitrate nitrogen does not bind to the soil but instead it moves freely with the soil water. Losses due to leaching and denitrification can be dramatic under adverse weather conditions resulting in economic and environmental concerns.
The RIGHT source, the RIGHT rate, the RIGHT time and the RIGHT place are the precepts for nitrogen management from the International Plant Nutrient Institute. There are numerous monitoring options to check on crop conditions and available nitrogen. Each year, the environment is different and information needs to be accumulated over time.
Nitrogen monitoring options offered by MISS
- In-season nitrate soil testing
- Before plant nitrate soil testing
- Plant tissue testing
- ASNT testing
- Stalk nitrate testing
INFORMED MANAGEMENT DECISIONS COME FROM COMPREHENSIVE DATA.
Soil nutrient sampling shows what is available to the plant from the soil. But what is in the soil is not necessarily what is in the plant due to many factors such as compaction, acidic soil that inhibits microbial activity, stress from insects or disease and so on. Tissue sampling can show what amount, sufficient or otherwise, is actually in the plant. Tissue sampling is an excellent trouble shooting tool.
As agriculture continually increases yields, more exact monitoring of plant needs is recommended. Since the first 10 percent of stress generally cannot be seen on the plant, a system of detection of plant needs such as tissue sampling is needed for top production. When pushing yields to the utmost capacity of the soil and crop varieties, tissue sampling for minor and micro nutrients, which have not been significant in the past, may now well be.
Amino Sugar Nitrate Test – ASNT
In 2006-07, MISS conducted a experiment in farmer’s fields using the amino sugar nitrogen test to determine the amount of nitrogen that the soil would supply by mineralization. The fields were grid sampled for P, K, OM, pH and ASNT. The fields had two strips of the farmer’s normal rate of N, one strip with a rate 20 pounds more than the normal rate and the rest of the field N was variably applied according to what would be expected from mineralization. The test was conducted on 3,000 acres in fields across the state of Iowa on varying soil types. The data was analyzed by Premier Crop of West Des Moines.
Except for one field, using ASNT in a formula to determine nitrogen rates, all fields made money using ASNT, either by reducing N or increasing yield. The example field shown was able to reduce N costs by about 10 dollars an acre while holding yields even. The colors in the example are from NDVI aerial imagery. The four small boxes in the field are zero N applied for a check. ASNT formula did not predict that one field with a very heavy manure history would have needed almost no nitrogen applied. There is no current or proposed N test that would help in determining correct N rates where past manure rates are heavy and/or unknown.
|Treatment||Units of N||Cost of N*||Low N by ASNT||High N by ASNT|
|Avg. based on ASNT||136||$44.88||96||192|
|*cost based on $.33/unit|
|Avg. OM||Low OM||High OM|
To get the full benefit of mineralization potential, soils need the proper pH, high fertility levels and have good soil tilth. Soils that are compacted or have poor drainage have less oxygen, which is critical for biological activity in the soil and controls the rate of mineralization. Acidic soils also inhibit biological activity.