Selecting compost and manures

Manures and composts come in may forms. In choosing to use any of them you should consider what you aim to achieve.

Mushroom compost has great levels of carbon and is terrific for building soil profile while not having an impact on nutrient levels.

Animal manures will have differing mineral analyses depending upon the source. Chicken (chook) manure contains good levels of phosphorous, while cow manure contains a greater overall mineralisation. All animal manures are a good source of the important minerals, nitrogen, potassium and phosphorous, and chook manure is also a good source of calcium.

All animal manures need to be used sensibly to avoid imbalance and nutrient run-off into the surrounding environment.  We need to strike a balance in garden inputs as an oversupply of nitrogen via manures can risk unhealthy nitrate contamination of our vegetables.

If manures are composted or purchased in a composted form then there is no risk of leaching or oversupplying nitrates because the nitrogen has been complexed and stabilised. Composting can increase the availability of the nutrients, introduce effective soil microbes and break down carbon into humus making it more effective in terms of water and mineral retention in the soil. Overuse of uncomposted material can lead to serious mineral imbalances and lock-up trace elements.

There is also the potential issue of weed seed contamination. Nitrogen in fresh manures is volatile and easily escapes into the atmosphere. Incorporating into a compost pile or digging the manure into the soil can help slow down this mineral loss.

Chook (chicken) manure is considered ‘hot’ when fresh. This means it is likely to burn delicate and sensitive plant roots and some soil microbes. It is a good strategy to compost this manure if that is possible. This manure has a fairly low carbon content unless it contains sawdust or straw.

Mushroom compost has a high carbon content but it is generally low in overall nutrient content. The pH of mushroom compost can range from 6.8 to 8. Preferably select a product with a pH below 7.

Cow manure and products made from cow manure have good levels of carbon and nitrogen but usually contains weed seeds as well.

Horse manure has great levels of carbon and breaks down quickly. Compost worms love horse manure but care needs to be taken to avoid manure straight after the animal has been wormed o vaccinated if it is to be used to feed worms. Once again there will the issue of weed seeds.

Green manure can be grown during the off-season or when resting beds in a rotation. Green manure crops build humus levels while feeding your beneficial soil microbes and earthworms. In warm areas try oats, Japanese millet, buckwheat, mung bean. In cooler areas, fava beans or fenugreek can be used.