By Lydia Balogh (summer student), Kathryn Carter and Christine Brown, OMAFRA

Composted manure (a mixture of animal manure and straw bedding) is a great option for grape growers to add to vineyards. Composted manure provides macro- and micro- nutrients to the soil and supplies organic matter to help build and maintain soil structure. The organic nitrogen within manure is mineralized and becomes available to vines slowly, supplying nitrogen in diminishing quantities to the soil over many years.

Composted manure pile waiting to be applied to a vineyard

Table of Contents

Is manure a good option for your vineyard?

Applying a manure to your vineyard will have minimal benefits if you have: vigorous grapevines, high organic matter (>5%), and petiole analysis show sufficient N and only one or two limiting nutrients. However, compost 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,
drought stress or leaf yellowing,
areas in the vineyard have compacted

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

When is a good time to apply compost 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 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. Manure needs to be incorporated completely to avoid nitrogen loss, which is easiest to accomplish before planting vines. Avoid applying manure around newly planted vines, as it may result in vine injury.

Poultry manure stored in the field, awaiting application after harvest.

What type of compost 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 compost growers apply in the vineyard often depends on local availability and transportation.

Should lab analysis be completed on compost prior to application?

There can be a large variation in nutrient content between different types of manures, so lab analysis is important to understand the nutrient availability in manure for your vineyard. Before applying compost in your vineyard, ask for tests to determine % Average Dry Matter, Available Nitrogen (N), Carbon: Nitrogen, 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.

How much manure should be applied to grapes?

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

Manure should be tested before application in vineyards, as the nutrient content of different manures varies depending on the livestock conditions. Application rates should be set on soil nutrient analysis and estimated available nutrients in both the soil and manure. In-field studies show that a low rate of compost applied regularly may be as good as a higher amount of applied compost, and therefore a high application rate may not be necessary.

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.

How to apply manure?

In late fall or early spring before planting, broadcast manure and incorporate it into the soil completely. Unincorporated manure will lose ammonia, and therefore have less nitrogen to supply to the vines. Fully incorporated manure also prevents phosphorous loss from runoff or erosion. 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 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 highly compacted soils that can benefit from improvements in soil structure and aggregate stability,
or new vineyards or replant sites that can benefit from soil conditioning