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Manure: Tackling the frequently asked questions


November 17, 2021
By Christine Brown, Field Crop Sustainability Specialist/OMAFRA

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When fertilizer prices start to increase so do the number of questions asked about manure! Manure is a carefully guarded treasure – brown gold – for livestock producers that have figured out the nutrient and organic matter value. However, with the increase in available organic amendments from municipal sources or from farms with more manure than landbase this is a relatively new concept for many crop producers that have access to manure or other organic materials.

Why bother with manure?

Manure is nutrient rich and organic matter rich. However, just as with commercial fertilizers, manure must be managed to ensure maximum availability and that the nutrients stay where they were applied. In addition to the nutrients found in commercial fertilizers (NPK), manure also has micro-nutrients, such as sulphur, zinc, manganese and calcium, and micro-organisms that benefit the soil and add microbial diversity. Similar to commercial fertilizers, the value is only as good as the distribution. Uniform application using calibrated equipment is essential.

What is the difference between liquid and solid manure?

Apart from the obvious differences between liquid and solid manures, the biggest difference is nutrient composition. Phosphorus tends to be higher in solid manure, while potassium tends to be higher in liquid manure. The nitrogen composition makes the nitrogen from liquid manure more like commercial nitrogen sources, while solid manure nitrogen behaves almost as a slow-release nitrogen form.

Figure 1. Injection of liquid manure.

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Figure 1. Injection of liquid manure.

When is the best time to apply manure?

Applying liquid manure just prior to planting or into a growing crop is the best method of maximizing nutrient utilization while minimizing environmental impact. Liquid manure applied in spring can supply over half of a corn crop’s nitrogen needs, while most solid cattle, sheep, or horse manure will require significant additional nitrogen. Solid manure from ruminants, applied in the fall will maximize available N for the subsequent crop while for most liquid manure spring or in-crop applications of liquid manure will maximize available nitrogen.

What rate should be applied?

Application rate will depend on:

  • general soil fertility levels of the field
    • fields with low fertility may have higher application rates to build fertility
  • frequency of manure application
  • crop needs
    • nitrogen from manure should not exceed two-thirds to three quarters of crop needs. Over application can result in crop lodging, increased disease pressure (e.g. white mould) and over application of phosphorus.
  • time of application
    • soil and weather conditions; forecast moisture and time to incorporation should impact application rate and timing. Care should be taken to prevent the movement of applied nutrients to off target locations.

Weather isn’t co-operating with my application plans. What are my options?

Soils are saturated and field tiles are running at full capacity. The following are a few options for manure application during a wet season. However, in doing so, risk of water contamination from subsurface drainage systems and surface runoff must be considered.

  1. Is this the year for custom application? A custom applicator with site specific or GPS capabilities can map where manure has been applied and at what rate, so that commercial fertilizer supplementation is easier.
  2. Consider alternative storage if available. Some neighbours may have under-utilized manure storage space.
  3. In ideal soil conditions manure injection is the preferred means of maximizing nutrients and minimizing environmental impact. However, injection of liquid manure is not as good an option in wet soils. Wet soils smear more easily, especially when combined with additional and concentrated liquids at each injection point. Surface application onto crop residue, or cover crops, followed by tillage at the earliest opportunity, will cause the least amount of compaction damage in wet soils.
  4. Nutrient loss from winter application is high risk and should not be a part of a manure application plan except as an emergency (contingency) plan. If manure must be applied to snow covered fields, consider the soil under the snow. If the soil is frozen under the snow cover, the risk of snow melt combined with rain leading to contaminated runoff is high. Where will the runoff move? The nutrients may not be where they were intended.
  5. Spread on fields or parts of fields with the least slope. Ideally, start with fields where there is no access to surface water. Water flow patterns are obvious in most fields during continued wet periods. Take note of those areas and avoid manure application where there is evidence of ponded water or “streams” through the field.
  6. Keep your distance from watercourses. Normally under good spreading conditions, the recommended distance between liquid application and the watercourse is 13 meters (40 ft). Under winter contingency applications, the separation distance should be increased. In the nutrient management regulations, the minimum setback for liquid manure application increases to 100 meters (330 ft) with winter application where slope to the watercourse is greater than 3%.
  7. Surface inlets or hickenbottoms are a direct connection to surface water. When soils are already saturated, the risk of water contaminated with manure moving through surface inlets increases
  8. Keep application rates as low as possible – 5,600 imperial gallons (6,800 US gal) is the equivalent to ΒΌ inch (6 mm) evenly applied across spread width. Consider the soil conditions at the time of application. If a quarter inch of rain fell in one minute, would it runoff or move?
  9. For all manure application options, monitoring is essential to ensure that contamination of water sources does not occur. Just in case, the Spills Action Centre number is 1-800-268-6060. Murphy’s Law – if the farm’s contingency plan has been reviewed in advance, it probably won’t be needed.

When should manure be incorporated?

Manure should be incorporated as quickly as possible after application. The key to incorporation is having the nutrients distributed uniformly though the seedbed. Injection is considered a form of incorporation. Injection is advantageous for reducing odour and decreasing loss from volatilization, especially with liquids.

How much fertilizer value will manure have?

Value of manure includes both the nutrient and organic matter value. Properly applied manure will out-perform commercial fertilizer and benefit longer term soil health. It is difficult to put a dollar value on organic matter and on micronutrients that may not be required immediately to meet crop needs. Value will depend on needs however; commercial fertilizer values have increased significantly in the past year. Fertilizer value varies with manure type and livestock type. Feed rations, storage and addition of bedding or waste water will influence the nutrients applied. It is recommended that manure is sampled for nutrient analysis (including micronutrients such as sulphur) at the time of application. For interpretation of available nutrients and value visit www.ontario.ca/agrisuite (organic amendment tool).

How do I take a manure sample?

A manure sample is most accurate and easiest to obtain at the time of application. The best method to know what nutrients were applied to the field is to take samples from various loads during application and then mix the subsamples to obtain one representative sample. If there is variation in the storage (not agitated or a solid manure pile), taking a sample for the first and last load each field where manure is applied will give more accurate results and reveal how much variation there is in the storage. Store the sample in a cool area until it can be sent to a lab. Any Ontario lab accredited for soil sample analysis will be able to analyze manure samples.