Spreading the load

This is especially important under shaded areas, where cattle congregate more in the hotter months.

It is recommended that manure depth and pen cleaning frequency be managed in a manner consistent with The National Guidelines for Beef Cattle Feedlots in Australia.

This will ensure that the depth of dry manure on the pen surface does not exceed 50 millimetres and maximum pen cleaning intervals do not exceed 13 weeks.

Pen surface has a significant impact on increasing heat load risk.

Higher manure loads result in surfaces that retain more moisture and take longer to dry out.

Wet pens also have a darker surface, absorb more solar radiation and become hotter than dry pads - which are a light brown to grey colour.

Wet pen surfaces can also increase the humidity within the pen, which reduces the ability of cattle to cool their bodies by evaporative cooling.

Frequent pen cleaning during summer reduces the average depth of manure over the pens.

This promotes more rapid pen drying and helps reduce the heat load risk - while also minimising dust during hot dry conditions.

While the removal of manure from feedlot pens is a substantial cost to feedlot operators, it is a rich source of nutrients and organic matter for use on agricultural land.

Current high prices for fertiliser indicate the demand for feedlot manure is only likely to increase.

The amount of nitrogen (N), phosphorus (P) and potassium (K) in pen manure depends on the composition of the manure excreted by the cattle - and on climate, pad conditions, pen cleaning practices and the use of dietary or pad additives that reduce volatilisation losses.

The nutrient content of excreted manure is influenced by the class of cattle, their diet, feed intake and other factors.

Gaseous losses of N as ammonia occur rapidly, and about 60-70 per cent of the initial N can be lost.

This N loss contributes to greenhouse gas (GHG) emissions and also reduces the future fertiliser value of the manure.

While some P and K is removed with the manure in runoff and deposited in the holding pond, these minerals are not lost as gas.

Stockpiling or composting manure can improve the handling by breaking up lumps while further reducing the total mass of manure dry matter, volatile nutrients such as nitrogen and often the moisture content.

But stable nutrients, such as P, can become more concentrated.

When designing or improving the manure stockpiling or composting area, it is important to ensure a durable, impermeable base, good site drainage and sufficient area.

It is a requirement that this area be within a controlled drainage area.

This usually involves the construction of diversion banks, or the use of natural topography to divert external "clean" runoff away from the area.

Runoff caught within the area must be directed to a holding pond.

Manure aging or composting is best undertaken using low windrows, rather than large piles. These are more manageable and less likely to catch on fire.

Windrows are typically constructed by forming manure into a long pile with a triangular cross-section, a base width of three to four metres and a height of 1.5-2m.

The apex and sloping sides promote water-shedding and prevent the manure from becoming too wet, which can result in significant odour.

Piles that are too low will not heat up, a process which assists decomposition, pathogen deactivation and weed seed destruction.

Piles that are too high may heat up excessively, particularly if they are not well compacted or contain wet manure.

Manure fires are a source of odour and smoke and can be difficult to extinguish.

So, wet manure from drains and sedimentation systems should be stored separately and allowed to dry before being added to windrows.

Manure composting is a more labour and capital intensive process than simply aging manure in static windrows.

Composting is the microbiological breakdown of organic matter into compost or humus.

Aerobic windrow composting uses organisms that need oxygen to function and is preferred over anaerobic composting because it minimises odour emissions, emits carbon dioxide rather than methane (lower net GHG emissions) and produces heat.

The benefits of composting manure include:

Composting consists of an active stage and a curing stage.

In the early part of the active stage, readily digestible sugars and starches are rapidly broken down and the temperature in the pile rises to more than 40°C (typically 50-60°C).

The temperature stays high for several weeks, providing there is sufficient nitrogen.

Next, the more resistant materials - such as lignin - are broken down and pathogens are suppressed.

Finally, the decomposed organic matter is converted into humus.

The correct moisture, temperature and turning of the material are important processes in composting.

The composting material has the ideal moisture content if it appears moist but little water can be squeezed from a handful.

The compost pile should be turned only after at least three consecutive days of high temperatures (of more than 55°C).

To kill pathogens and weed seeds, the pile should be turned at least three times during the active phase - which may take three months or more.

Fortnightly turning will minimise labour and create good quality compost.

But the pile can be turned more frequently if it has heated sufficiently and equipment and labour are available.

A strong temperature rise after turning indicates that active composting is still occurring.

If the temperature does not rise markedly - with the correct moisture content - the compost can be kept in a windrow, or formed into a stockpile where it can cure for at least a month.

Curing is important, as immature compost may have high organic acid levels, a high carbon to nitrogen (C:N) ratio and other properties that can be detrimental to crops.

Further information about the removal, handling and further processing of manure is available in the Meat & Livestock Australia (MLA) "Beef cattle feedlots: waste management and utilisation" manual.

This manual is comprised of five sections describing best-practice guidelines for the management of the main wastes of the feedlot - namely manure and effluent - and is available for download from the MLA website.

If any readers would like the link to this document, or any other information relating to feedlot operations, please feel free to contact me directly.