By Kathryn Carter, Stephanie Vickers, Danny Jefferies, OMAFRA and Lydia Balogh

Composted manure is animal manure, sometimes with straw bedding, shavings, or feed waste added, that has been aged or decomposed for some length of time and has a relatively stable nutrient content. Composted manure is a great option to apply to vineyards to add macro- and micro- nutrients to the soil, increase organic matter (OM) and to help build and maintain soil structure. As the organic nitrogen within composted manure is mineralized it is slowly available to the vines, supplying nitrogen in diminishing quantities to the soil over many years. Once compost is applied to the vineyard floor, its effects (good or bad) are difficult to undo. The effects of composted manure will remain in the soil and be evident in the vine for 5 to 7 years after the application. As a result, it is important to determine how to best use composted manure without causing long term problems.

Is composted manure a good option for your vineyard?

Applying composted manure to your vineyard will have minimal benefits if you have: vigorous grapevines, high organic matter (>5%), and petiole analysis showing sufficient N and only one or two limiting nutrients.  However, composted manure might be a good option in vineyards if:

• petiole analysis shows the need for N and other macronutrients,
• areas in the vineyard show signs of low vigour,
• areas in the vineyard show drought stress or leaf yellowing,
• areas in the vineyard suffer from soil compaction,
• the goal is to improve soil water holding capacity and infiltration rates,
• there is a desire to increase organic matter in vineyards.

In addition, it may be beneficial to apply composted manure to vineyard replant sites for pre-plant soil conditioning and to improve soil structure.

When is a good time to apply composted manure to grapes?

It’s best to apply composted manure in late fall or in the early spring (before bud break to pea-sized berries). Avoid applying composted manure from bunch closure to harvest; this timing may cause excessive growth, poor grape quality, reduced storability, and delayed cold-hardening of vine woody tissue, impacting winter acclimation. When applying prior to planting, composted manure should be incorporated into the soil to prevent nutrient losses from runoff, erosion or volatilization. In established vineyards, composted manure can be broadcast across the entire vineyard or band-applied under the vines and incorporated, if possible.

Don’t apply manure around newly planted vines, as it may result in vine injury.

Avoid spreading manure on frozen or snow-covered ground, and when there is a high potential for runoff, such as when the soil is wet or rain is predicted.

What type of composted manure should I use?

Only use well-composted manure in vineyards. Raw manure before composting may contain weed seeds, plant pathogens, and have unpleasant odours. Nutrient availability from raw manure is not as predictable as that of composted manure, and if applied, could result in excess availability of salts and leaching of nutrients. Composted manure should be uniform in colour and texture, have neutral to earthy odour, and a carbon to nitrogen ratio less than 20. Composted manure is stable in nutrients/organic matter, has been composted in a pile for six to ten months and has obtained a temperature of 130-140° F for at least one week. The type of composted manure growers apply in the vineyard often depends on local availability and transportation.

Should lab analysis be completed on composted manure prior to application?

Grapevines generally require less fertilization than many other crops, as growers are seeking to find a balance of vegetative growth and fruit yield. Understanding the nutrient levels in compost is important as excess nitrogen can cause high vigour, poor fruit quality, and inadequate winter acclimation in some climates. 

Additionally, there can be a large variation in nutrient content between different types of composted manures, so lab analysis is important to understand the nutrient availability in manure for your vineyard. Before applying composted manure in your vineyard, ask for tests to determine % Average Dry Matter, Available Nitrogen (N), Carbon: Nitrogen ratio, Available Phosphate (P₂O₅), and Available Potash (K₂O), Potassium (K), Magnesium (Mg), Boron (B), Soluble salts, and pH. Applying manure based on lab results will allow you to adjust inorganic fertilizers accordingly and reduce the chance of excessive nitrogen and other nutrients in the soil. You can learn more about interpreting a detailed organic amendment analysis at this Link.

How much composted manure should be applied to grapes?

Composted manure applications are best applied based on soil and petiole analysis. Guidelines for testing soil and leaf petioles in vineyards can be found at Soil management, fertilizer use, crop nutrition and cover crops for fruit production.

Application rates should be set on soil nutrient analysis and estimated available nutrients in both the soil and manure. Compost contains a wide range of macro and micronutrients including nitrogen, phosphorous, potassium, calcium, magnesium, boron, iron, copper and manganese. Sites that require only a small amount of a single nutrient (potassium) may be better addressed using a commercial fertilizer.

The nitrogen in manure is not all immediately available to vines after application, with only 50-60% of the nitrogen in manure available during the first year after treatment. The remaining nitrogen will slowly become available in future growing seasons, with up to 10% of the residual nitrogen available in the following year.  OMAFRA recommends that 30 lbs nitrogen/acre (34 kg nitrogen/ha) each year is adequate for most vineyards. Inorganic nitrogen fertilizers should be adjusted to complement the nitrogen supplied by manure. The Organic Amendment module in AgriSuite can help you decide how much composted manure to apply, based on the lab analysis.

Storing composted manure

Composted manure should be stored in a place to minimize the risk of contaminating water sources and prevent complaints from neighbours and local residents. Safe storage of compost is critical, especially during heavy and frequent rainfalls, as it also will save growers money, and prevent any material from washing away in the rain.

Here are some guidelines to help determine the best place for temporary storage of manure.

Proper temporary storage of manure can help to reduce the environmental risks associated with manure and can improve relations with neighbours.  For additional information refer to OMAFRA Factsheet, Temporary field storage of solid manure or other agricultural source materials.

What are the food safety risks associated with manure use?

Grapes in the field can become contaminated with pathogens that cause human illness if they come into contact with manure and manure-based composts. Pathogens within manure can survive from 1 to more than 300 days after field application of fresh manure. However, proper composting of manure reduces pathogens to acceptable levels. Proper composting of manure requires that it is heated to 55°C for 3 days to reduce pathogen levels. Manure should not be applied to vineyards where grapes will be harvested within 120 days.

Conclusion

The use of composted manure in vineyards can be of benefit in vineyards that:

• need N fertilization and other macronutrients,
• need organic matter,
• have compacted soils that can benefit from improvements in soil structure, aggregate stability, and infiltration,
• or new vineyards or replant sites that can benefit from soil conditioning