The Value and Application of Manure on Forages

Table of Contents

1. Guidelines for Manure Applied to Forages
2. Nutrients and the Crop
3. Table 1a: Nutrient Removal of Common Field Crops (Metric)
4. Table 1b: Nutrient Removal of Common Field Crops (Imperial equivalents)
5. Nutrients in Manure
6. Table 2a(i): Average Amounts of Available Nutrients in (kg per tonne) for Different Types of Solid Manure (Metric)¹
7. Table 2a(ii): Average Amounts of Available Nutrients in (kg per tonne) for Different Types of Liquid Manure (Metric)¹
8. Table 2b(i): Average Amounts of Available Nutrients (in lbs. per ton) for Different Types of Solid Manure (Imperial)¹
9. Table 2b(ii): Average Amounts of Available Nutrients (in lbs. per thousand gal.) for Different Types of Liquid Manure (Imperial)¹
10. Table 3: Approximate Ammonium Nitrogen Levels Available by Livestock Type
11. Table 4: Estimated Loss (%) of the Ammonium-Nitrogen Fraction Due to Weather and Soil Conditions
12. Related Links

A high producing forage field, whether legume, grass or a mix of legumes and grass has a high need for nutrients. The nutrients of manure can work as well as commercial fertilizer, therefore utilizing manure and potentially saving money by not needing to purchase commercial fertilizer.

Nutrient management planning has changed manure from a waste product that must be disposed of, to a useable resource with nutrients and organic matter benefits. Farmers are considering alternative options for manure application, both for crops to which manure can be applied and for timing of application.

Guidelines for Manure Applied to Forages:

Listed below are some guidelines and precautions for applying manure to forage crops. More detail regarding crop nutrient needs, manure nutrient content and precautions necessary for optimum animal and crop production follow the guidelines.

1. Use a manure analysis that indicates ammonium nitrogen content of the manure to help determine most appropriate application rate. The ammonium nitrogen content of manure is variable between livestock types and from farm to farm. Applying at a rate too high in ammonium nitrogen could cause burn damage to regrowth. When an analysis is not available, usually a rate near 45,000 litres/ha (4000 gal/ac) (with the exception of liquid poultry manure and highly concentrated liquid hog manure) is safe for an alfalfa stand. Since the NH₄-N content in solid manure is relatively low, nitrogen burn to new growth is not a concern (with the exception of high rates of poultry manure).
2. Manure can be used at relatively high rates before seeding a new forage crop. Manure should be applied and incorporated at least 5 days before planting. High nitrogen and/or salt content in manure can lead to severe root injury in new seedlings which will reduce plant stand. New seedings may also have higher weed pressure when manure is used prior to planting.
3. Apply manure to the oldest and/or grassiest forage stands first, since they will benefit most from the nitrogen and potash.
4. Apply manure as soon as possible after harvest, before regrowth. This will prevent manure contact and potential nitrogen burn on new growth.
5. In sunny hot weather, apply manure during late afternoon or early evening to minimize nitrogen loss and reduce potential nitrogen burn. Twelve to 18 hours without direct sunshine and with potential dew will reduce manure volatilization.
6. A gentle rainfall - 10 to 12 mm - will help incorporate the nitrogen from manure. An erosive rain will increase risk of surface water contamination. Since manure spread on forages is surface applied without incorporation, odour can be an issue, especially for fields located near residential areas.
7. Avoid applying manure when soil conditions are wet. Wheel traffic from a heavy tanker will cause some crown damage and potentially some compaction; another reason to apply to older stands. Irrigating manure will cause less damage to crowns, however will usually be applied less uniformly and with greater nitrogen loss and more odour. Note: Irrigation of manure greater than 1% dry matter will be banned beginning July 1, 2005 under Nutrient Management regulations 267/03.
8. Applying manure uniformly is difficult. Rates under 34,000 litres/ha (3000 gal/acre) are hard to apply without applicator modification due to high tractor speed requirement.
9. Where solid manure is being applied to forages extra caution should be exercised since in most cases the manure is not applied uniformly enough. When manure "clumps" it can cause a significant reduction in the crown stand.
10. Precaution should be taken for manure applied to forages that will be used for round bale silage. In some cases where manure was applied to regrowth, the bacteria from manure has caused improper fermentation, which can lead to problems (spoiled areas) in silage.
11. Disease transmission from manure in forages has not been reported as an issue, however the question does come up periodically. If there is a concern about a particular disease being carried in the manure, question a local veterinarian about how the disease is transmitted. If the disease is carried in manure, then question how long can the organisms survive in the soil, under normal weather conditions.
12. Biosolids, specifically sewage sludge, have almost no potash. Forage crops have high nitrogen and potash needs. Since nitrogen is naturally produced by legume crops, legume forages have traditionally not been the best economic target for the nitrogen from manure and biosolids. Livestock manure is a good source for replacing commercial potash; in contrast, biosolids are a poor choice for replacing potash needs of the crop.
13. Precaution: high soil test levels of potash and high potash levels in manure can lead to high potassium (K) levels in forages resulting in milk fever problems in dairy cows. Alternatives to high K forages include off-farm sources of low K hay and/or dilution with low K forages such as corn silage, or anion/cation balancing of the ration.
14. When applying manure to forages, additional commercial fertilizer (particularly potash) applications should be reduced to compensate for nutrients applied from manure.
15. Precaution: Manure containing high levels of copper (i.e. from farms using hog rations high in copper and/or cattle footbaths containing copper sulfate) should never be applied to sheep pasture. Sheep have a low requirement for copper; their maximum tolerable level is close to their requirement. A 57,000 litres/ha (5000 gallons/ac) application rate containing a copper level of 5 ppm applied to pastures could raise the copper level of the forage to toxic levels for sheep.

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Nutrients and the Crop:

Nutrients removed by a crop will vary with soil type and with moisture levels from year to year. Existing soil fertility levels will also influence nutrient uptake for the crop. Some nutrients, when at high levels in the soil (for example: potassium) will cause "luxury consumption" by the plants. In hay production this can be significant for potassium, since high soil test levels usually result in high potassium levels in both legume and mixed hays. This can cause milk fever problems in dry dairy cows. The potassium content of hay should not exceed 2.5% of DM. Total ration should be less than 1.2% of DM total. dry matter content. Alternatives to high K forages include anion/cation balancing, off-farm sources of low K hay or dilution with low K forages such as corn silage.

Crop Removal = (Base Value) x ( Estimated Yield ÷ Base Yield)

For example:

Mixed Forage K₂0 Removal = (300 lbs/ac) x (6 ton/ac ÷ 5 ton/ca) = 300 lbs K₂0

For this example, there is 360 lbs/ac K₂0 removal, for a 6 ton/ac mixed forage crop.

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Table 1 shows the approximate nutrient (nitrogen (N), phosphorus (as P₂0₅), and potash (as K₂0)) removal from common crops at a base-level yield. For example, shows that alfalfa-grass hay crop (5 tons/ac dry matter (DM) yield can remove about 314 lbs of nitrogen (N), 65 lbs of phosphorus (P₂0₅) and 300 lbs of potash (K₂0) from the soil. At a 6 ton/acre DM yield, the crop could remove 378 - 78 - 360 lbs/ac N-P₂0₅-K₂0.

Knowledge of soil fertility levels using regular soil testing, combined with knowledge of what nutrients are removed by the forage, and nutrients replaced by manure applications will help determine additional commercial fertilizer needs. An application of about 39 kg/ha (35 lbs/ac) of P₂0₅ will increase the phosphorus soil test (sodium bicarbonate) by 1ppm while the application of about 22 kg/ha (20 lbs/ac) of K₂0 will increase the potassium soil test (ammonium acetate) by 1 ppm.

Legume crops are unique in their ability to produce nitrogen. Nitrogen is added to the system through the action of symbiotic bacteria (Rhizobia sp.) inhabiting nodules on the legume roots. These bacteria convert atmospheric nitrogen into ammonium, which then becomes available to plants. However, if the nitrogen is supplied from manure, the nodules become "lazy" and the nitrogen from the manure is used first. This helps to prevent the risk of nitrogen contamination for groundwater; however, an erosive rainfall soon after application has the potential to contaminate surface water.

Nutrients in Manure:

It is essential to know the approximate nutrient content of the manure being applied to forages. This is best done by taking a representative manure sample for analysis. (Procedure for taking a sample can be found in the manure section of Pub 811, Agronomy Guide.) The nutrient content of manure is variable between livestock types and from farm to farm. Applying a rate that is too high in certain nutrients could cause plant damage, and/or nutrient imbalances inbalances in the future.

²Total useable nitrogen is based on spring application, incorporated within 24 hours.

³Value of manure is based on purchase price of an equivalent amount of available nutrient as mineral fertilizer. The actual value for crop production will be less if all the nutrients applied are not required for growing the crop.

⁴ An application of about 39 kg/ha of P₂O₅ will increase the phosphorus soil test (sodium bicarbcarbonate) by 1ppm while the application of about 22 kg/ha of K₂O will increase the potassium soil test (ammonium acetate) by 1 ppm.

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²Total useable nitrogen is based on spring application, incorporated within 24 hours.

³Value of manure is based on purchase price of an equivalent amount of available nutrient as mineral fertilizer. The actual value for crop production will be less if all the nutrients applied are not required for growing the crop.

⁴ An application of about 35 lbs/ac of P₂O₅ will increase the phosphorus soil test (sodium bicarbcarbonate) by 1ppm while the application of about 20 lbs/ac of K₂O will increase the potassium soil test (ammonium acetate) by 1 ppm.

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Table 2 shows the average nutrient values for various types of manure. There are two nitrogen components in manure. Ammonium nitrogen (NH₄-N) makes up the largest percentage of the nitrogen in liquid manure, with approximate percentages listed by livestock type in Table 3. The organic nitrogen component is available over time as the organic matter breaks down. About 20 percent of the organic matter component of manure is assumed to be available to a growing crop during the year of application. The percentage is generally higher in poultry and lower for manure from ruminants on a mainly forage ration.

Adapted from Beauchamp, 1995

Manure nitrogen, once applied, has three potential routes. It can disappear into the atmospherethin air, into soil below the plant root zone, or it can be utilized by crop growth. When manure is applied to the soil surface, the opportunity for ammonium nitrogen volatilization exists. The extent of ammonia volatilization is dependent on many factors including temperature, soil moisture, soil pH, vegetative cover, rainfall and extent of infiltration into the soil. Warm sunny dry weather is conducive for highest potential loss while cool, cloudy conditions when soil moisture is high prevents rapid loss. When manure in incorporated or injected into the soil, most of the ammonia loss is avoided. Rainfall, not heavy enough to cause erosion, but at least 10 mm, shortly after application will also help to reduce ammonia loss from manure that is not incorporated.

Related Links

• Publication 811: Agronomy Guide for Field Crops

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