Managing Livestock Manures 4: Managing Manure on Organic Farms

Nutrient planning

Maintaining soil fertility depends on the balance between nutrient inputs (from all sources) and removals in crops and as losses. In many organic systems, manures are valued for their phosphate, potash and organic matter contents, but the nitrogen component should not be forgotten especially where it is the limiting nutrient on the farm.

Planning at the farm level

Estimate the nutrients in manures produced on-farm (and in any imported manures) or permitted fertilisers.

Use standard figures, animal types and numbers to calculate nutrient production on the farm (e.g. Appendix IV). Where possible use actual estimates based on store size and analysis of manures reliable estimates may require measurements over a couple of years.

Calculate imported nutrients from manure nutrient content (Table 1 or Table 2) and weight/volume imported.

Use these data to plan where the manures would best be used in the rotation, in terms of their nutrient supply.

Divide total manure N (in kg) by 170 (the application limit in the EU Livestock Directive) to check that your organic unit is large enough to accept the manure.

Planning at the field level

Know the weight or volume of the manure to be applied.

Know the nutrients applied to a field by using standard values for nutrient content (Table 1 or Table 2) or analysing the manure and multiplying by the weight to be applied.

Decide on the best application time, depending on the type of  manure and the crop to be grown.

Wherever practical, try to minimise losses of ammonia and nitrate, thus conserving nitrogen for use by the crop.

The use of farm balances

Organic systems aim to ensure that soil fertility is at least maintained, without damage to the wider environment. The farm nutrient balance is an important tool to check this. There are several calculation methods, either at the farm or field level. All calculate nutrient inputs (feed, fertilisers, atmospheric deposition, N fixed by legumes, etc.) and outputs (crop and animal produce, nutrient losses etc.). Balances are useful to test if a farming system is viable; a large negative value (removal of nutrients far in excess of inputs) would suggest only short-term sustainability. A small positive value in the balance of N, P and K is probably the ideal.

Ask your Sector Body or consultant for more information about how to calculate nutrient balances [NB there is a farm and field nutrient balance in the EMA Software].

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