New life for damaged hay

Heavy rain and flooding can spoil stored hay. Options for recouping this investment are few and include using the bales to fill old gullies, spreading hay over the surface of paddocks and allowing pasture to grow through, or composting the spoiled hay.

Of these options, composting has the greatest potential to return some benefit to the farm.

Aerobic composting is the rapid decomposition of organic materials into a humus-rich product ideally suited to soil improvement.

High temperatures are naturally generated during the composting process resulting in the destruction of any weed seeds and pathogens that may be present in the raw organic materials.

If your farm produces sizeable quantities of 'waste' materials each year (spoiled hay, silage or manures), then composting is a good way of improving your soil and extracting extra value from what was previously often regarded as waste.

Composting methods

While there are numerous composting methods available, the most simple and costeffective for farmers is the ‘turned windrow’ method.

A compost windrow

This involves piling organic materials in correct proportions and with adequate moisture, in rows on a suitable surface and then mixing well. The dimensions of the windrow depend on:

• types of materials being composted;

• space available; and

• equipment being used.

For a manure-based operation, the height of the windrow will be typically around 1.5m, with the base at two to three metres wide. The length of the row can be as long as space permits.

Many farm wastes (manure, hay, silage and sawdust) can be composted with minimal pre-treatment. Other wastes that become available from time to time (woody wastes) may need to be chopped up because they are too coarse.

Once the wastes are correctly mixed in the right proportions, and at the right moisture content, the composting process will begin.

All you need to do is provide organic materials in the right proportions, with moisture, and the microbes will do the rest.

Understanding the conditions required by the composting microbes is paramount to successful composting.

Micro-organisms have three basic needs and when these are provided, the composting process will proceed and the mix will heat up.

These needs are:

• oxygen;

• adequate moisture; and

• suitable food supply.

Oxygen

Fresh air contains 21 per cent oxygen but inside the composting pile microbes will be actively consuming oxygen.

Oxygen percentages of greater than 10 per cent inside the pile are adequate but when levels drop to around five per cent, the activity of the microbes will slow.

In oxygen-deprived piles, anaerobic microbes will begin to dominate and unlike the aerobic microbes, these can produce foul smells.

Aeration is maintained by physically turning the pile, and also ensuring that the feedstock contains a mix of small particles and larger air-trapping particles.

Wastes such as manure can have high moisture contents and, if not well-mixed, can impede air flow.

Such material should be mixed with structured wastes such as straw or woodchips.

Waterlogging of the pile (from rain), over-watering or poor structure can create an oxygen poor environment — so moisture levels need to be monitored.

Moisture

Composting microbes need adequate moisture to survive and the ideal moisture content is around 50 to 60 per cent.

Another way of determining the moisture content of your compost is to assess it by hand.

Ideally compost should appear wet, but when a handful is taken and squeezed hard, moisture should be visible but not run out of your hand. At 50 to 60 per cent moisture content, the compost will hold its form after squeezing, and resist crumbling.

If the compost is too dry (below 30 per cent moisture content) microbial activity will be restricted, and if it’s too wet (greater than 60 per cent) conditions will become anaerobic and unfavourable microbes will flourish, creating nasty smells.

Adequate moisture levels should be established when the mixture is first created.

As the microbes consume the compost materials they will generate heat, causing water to evaporate from the pile. This is a beneficial process as it moderates the temperature of the pile — it is important that this

moisture is replenished.

Moisture content should be assessed at every turning, and additional water applied using a hand-held or soaker hose as required.

Stockpiled spoiled hay is often very dry and can be difficult to re-wet. Trying to wet the hay at the same time as mixing it with manures can be very difficult.

It is best to spread out the hay, some time in advance of making the pile, using a bale processor where the row is to be established and allowing time for rain to thoroughly wet the hay. Alternatively, a soaker hose that slowly applies water will do the job.

Carbon to nitrogen ratio and nutrients

The carbon to nitrogen ratio of the compost feedstock will have important implications on the speed of the composting process.

If there is too much nitrogen, the

pile may heat up too quickly and loss of nitrogen in the form of ammonia can occur. If there is too little nitrogen, the pile may not heat up enough and the compost may take much longer to break down.

The ideal carbon to nitrogen (C:N) ratio at the start is about 30:1 — 30 parts of carbon by weight to one part of nitrogen. In practice, an initial C:N ratio of between 25 to 40:1 is usually quite sufficient. This will gradually fall to 10 to 20:1 as the carbon in the pile is digested.

Other nutrients are also needed by the microbes in addition to carbon and nitrogen. These include:

• sulphur;

• phosphorus; and

• other trace elements.

If animal manures are a primary ingredient of the compost, then these elements are usually in plentiful supply.

A variety of pH levels are conducive to composting. At a pH above nine emissions of ammonia production may present a problem. This is unlikely to be an issue if normal organic ingredients are used.

Temperature

Heat is naturally generated by microbes as they digest waste materials. This heat will build up within the piles, with the highest temperatures occurring in the centre.

The ideal range for effective composting is between 45°C and 65°C, and to maintain temperatures within this range the pile should be monitored and turned or watered as necessary.

Temperature can also be used as an indicator of how the composting process is progressing.

The early stages will see the temperature climb quickly — assuming the pile has been properly constructed. Heating occurs due to the rapid increase in biological activity in the pile and the consumption of available food by the microbes.

During this early phase (week one to two) the pile will need the most attention to prevent over-heating.

Careful monitoring of temperature is necessary to know when to turn a pile. The temperature should not be allowed to go beyond 70˚C. Once 65˚C is reached, the pile should be turned to blend cooler material from the outside to the inside, ensuring evenness of the final product.

During this process, care should be taken to assess the moisture content.

If the material is too dry or has dry

sections, moisture must be added for proper composting to continue. Once reformed, the pile will again heat up. Temperature monitoring will provide the feedback necessary to know when to next turn the pile.

As time goes by, the pile will heat up less quickly and after the first couple of weeks, will no longer achieve 65˚C. This occurs when the easily digestible feedstocks are depleted and microbial activity declines.

Once temperatures fall below 45˚C, fungi become progressively more important, particularly in the latter stages of decomposition, due to their superior ability to degrade more complex organic compounds such as lignin and lignocelluloses.

When the compost reaches near ambient temperature, and turning does not result in significant changes in temperature, the composting process is complete.

Heat is an important consideration in ensuring that your compost has been rid of any pathogens or weed seeds.

In order to be confident that the compost is pasteurised, the whole mass needs to have reached temperatures higher than 55˚C for at least three days.

This means the pile must reach a minimum of 55˚C following five turns so that every part of the compost has been subject to high temperatures.

Selecting a site

Site selection is a pivotal factor influencing the success of a composting operation.

Ideally, composting should be conducted on a level, compacted surface. Suitable surfaces include concrete, crushed rock or gravel and compacted soil.

Other considerations include:

• distance from composting site to the paddock;

• access to compost ingredients and water;

• avoiding potential odour complaints;

• wind direction;

• distance from surface

water;

• proximity to groundwater;

• slope; and

• run-off storage.

Curing and storage

When temperatures in the compost are within 10°C of ambient, and turning no longer results in a rise in temperature, the compost may be ready for use.

However, it will benefit further from a short (three to six weeks) period of curing.

Curing reduces the likelihood of experiencing plant toxicity effects that can sometime occur with the application of fresh compost. Curing also promotes the formation of stable and complex humus compounds.

During the curing phase the compost will not require turning.

Stable compost can be stored for longer periods.

Care should be taken not to contaminate stable, finished compost with potential pathogens and weed seeds that can be transmitted on equipment.

Care should also be taken to prevent the pile becoming saturated or flooded.

Application

Annual crops:

For annual crops, apply compost before sowing — ideally two months ahead.

This allows the compost to become integrated into the soil to start soil conditioning and biological stimulation.

Ideally compost should be incorporated or at least 'tickled' into the surface soil. Perennial pastures:

For perennial pastures, paddocks should be grazed down before compost is applied.

This enhances contact with the soil surface and pasture re-growth will quickly shade the compost and prevent it drying out or blowing away.

Compost can also be surface-applied under perennial crops (trees, shrubs and vines) where it will slowly decompose or be drawn into the soil by the action of worms and other invertebrates.

Application rates

Application rates should not exceed 60 cubic metres/hectare/year on high value crops.

Higher rates will be uneconomical and can result in nutrient losses in the same way that inorganic nutrients can be lost if over-applied.

Broadcasting compost is the easiest way to improve soil conditions across a whole paddock.

Restricting application to planting beds, placement in trenches or banding can be used to reduce total application requirements and costs.

In practical terms, application rates for perennial pastures or cropping are likely to be in the order of one to seven tonnes/hectare/year.

The cost of this is highly dependent on the degree to which farmers have:

• access to compost material;

• labour costs; and

• machinery costs.

As a general guide, farmers report costs in the order of $100 to $250 to make and spread three tonnes of compost per hectare.