1.- Total Kjeldahl Nitrogen (TKN) is the total amount of organic and ammonia nitrogen in the sample.
2.- Ammonia nitrogen (NH3) is the amount of inorganic nitrogen that is readily converted to plant available forms.
3.- Organic nitrogen is determined by the difference between total nitrogen and ammonia nitrogen.
Method of Liquid Manure
Application
|
% N Loss
|
*broadcast, no incorp. (2-3 days)
|
25-35
|
broadcast, immediate incorp. (< 2 days)
|
15-25
|
broadcast, no incorp. on cover crops
|
35
|
injection
|
0-2
|
*irrigation (3 days or less)
|
25-35
|
*If time to incorporation
is greater than three days, nitrogen losses can be 40-60 per cent for
broadcasting and 60-80 per cent for irrigation. For solid manure, volatilization
losses from broadcasting may be less than those reported for liquid manure.
|
- high soil pH (>7.0);
- soils high in calcium carbonate (lime);
- soils with low retention ability for ammonium: e.g., low clay content, low organic matter, low cation exchange capacity;
- high soil or atmospheric temperature;
- liquid fertilizer applied onto dry soil;
- high wind velocity and/or highly aerated soils;
- high rate of fertilizer application;
- depth of incorporation/penetration < 2 cm.
- coarse-textured or extensively cracked soils
- high concentration of nitrates in the soil profile due to excessive applications of nitrogen fertilizers, including manure
- significant precipitation to move nitrates downward
- limited plant root zone (due to plant species, time of year) to intercept nitrates
- groundwater table present (higher risk if closer to surface)
- use of irrigation
- Identify areas in the landscape where nitrate leaching into groundwater is most likely to occur (these are usually areas with coarse-textured soils and shallow water tables)
- Test soil every year. Manitoba's Farm Practices Guidelines recommends no more than 150 lb/ac of nitrate-nitrogen in the top four feet of the soil profile and no more than 20 lb/ac of nitrate-nitrogen in each subsequent foot of the profile. Refer to Appendix F, Monitoring Soil Nitrate, in Manitoba's Farm Practices Guidelines.
- Monitor groundwater levels and sample groundwater for nitrate content annually or when possible. Environmental guidelines have set 10 parts per million (ppm) as the maximum nitrate content for drinking water consumed by humans.
- Apply only as much nitrogen fertilizer to the crop that can be used in one growing season. Adjust commercial nitrogen fertilizer additions when manures have been applied.
- Minimize the window of opportunity for nitrate leaching. The time when nitrate is present in the soil to the time when it is utilized by the crop should be as short as possible. Spring applications are less risky than fall applications, and split applications of nitrogen during the growing season are less risky than applying all the nitrogen at the time of planting.
- If high levels of nitrate-nitrogen are found below four feet, use crops suited to your operation for retrieval of deep-leached nitrates.
- soils with high organic matter (5 per cent or greater);
- limited oxygen, due to high water content, rapid respiration or compaction;
- neutral or alkaline pH (7.0 or greater);
- temperatures > 2oC;
- chemodenitrification (denitrification without microbial activity) requires low pH, but may be significant in freezing soils with high salt concentrations and high nitrite content.
- Avoid high applications of nitrogen to areas in the landscape with high water tables and intermittent ponding.
- Follow the same practices to prevent nitrate leaching.
- Incorporate manure as soon as possible.
- Test soil regularly to monitor nitrogen utilization and possible losses.