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Ammonization of Straw and Chaff

It is recommended that producers leave the straw on the land and collect chaff for feed, especially in the brown and dark brown soil zones. Straw left on the land preserves soil tilth and helps prevent erosion. When faced with a feed shortage, a decision must be made whether to remove the straw for feed or to look for more feed elsewhere.

Ammonisation is a method of treating low-quality hay and crop residues, such as straw and chaff, to im­prove their nutritional value as feeds for ruminant animals.

Ammonisation improves feeding quality by increasing the amount of total digestible energy (TDN) in the residue, the amount of roughage the animal will consume and the crude protein equivalent (CP). It involves sealing the residue or hay in a gas-tight enclosure and adding anhy­drous liquid ammonia supplied by fertilizer dealers. As long as the air temperature is 10° C or warmer, the chemical reaction is complete in 21 days.

Chaff fits into self-feeding systems for calves as well as cows.

No problems have been reported with the feeding of ammoniated chaff or straw. Abortions, calves with low birth weight, or reproductive problems have not been associated with ammonisation. Rumen impaction should not occur, provided the total energy intake is adequate. Ammonisation of straw or chaff reduces the grain requirement but does not eliminate it.

Sampling prior to ammonisation. Straw or chaff intended for ammonisation should contain at least 12 per cent moisture, and preferably 15 to 20 per cent. Wheat straw or chaff should have a TDN of at least 33 per cent and barley straw or chaff a TDN of at least 38 per cent to be eligible for ammonisation.

To ensure that the moisture content and feed quality of your straw or chaff are adequate for ammonisation, submit a representative sample to a feed testing laboratory for analysis. Mix small amounts of straw taken from different parts of the field or the stack so the analysis will truly represent your material.

When to Ammoniate

A minimum moisture level of 12 per cent is necessary for efficient ammonisation. This can be achieved by baling early in the morning after heavy dew or by baling as soon as possible after a rainfall.

Usually, chaff collected from combining a swathed cereal crop is very dry, containing eight to 10 per cent moisture. The moisture content must be increased to 15 to 20 per cent, or a satisfactory improvement in digestibility may not be obtained. This can easily be accomplished by attaching a 15 to 20 foot (4.5 to six metre), one half inch (1.27 centimetres) copper pipe to a garden hose, perforating the final three feet of the pipe and calibrating it for water delivery. The pipe can be inserted and withdrawn throughout the stack until the right amount of water has been added.

For example, to increase the moisture content of a 40 ton chaff stack by five per cent, 400 gallons of water will be required (40 X 2000 X .05/10) or in metric (40 tonnes X 1000 kg X .05 = 2000 litres). Then measure how many gallons (litres) per minute run through the pipe. Insert the pipe into different locations in the stack and add water for the total required number of minutes to get the proper volume of water into the stack.

The efficiency of ammonisation is also dependent on temperature; the higher the temperature, the better the result. Generally, it is advisable to ammoniate early in the fall, before temperatures become too cold.

Location of the stacks

Each stack should be a) downwind and some distance from the farm buildings and cattle holding area; b) accessible to farm machinery from all sides; c) accessible at both ends so that the ammonisation pipes may be inserted; d) placed near some shelter which will reduce or prevent wind damage.

Building the Stacks or Piling Chopped Straw or Chaff

The dimensions of the stack or piles are determined by the size of the plastic sheet to be used to cover them. Six-millimetre, black polyethylene is available in sheets 100 feet long by 40 feet (30.5 metres X 12.2 metres) wide. The stacks or piles must be constructed in such a way that an overhang of at least two feet (0.6 metre) of plastic is left on each side and at each end to seal the enclosure properly.

The plastic cover is particularly susceptible to damage from the corner bales of stacks constructed from rectangular bales. To protect the plastic, cover the corner bales with grain bags or plastic fertilizer bags. It is also wise to cover the whole stack with a used plastic underlay.

Depending on the size of the bales and the plastic, round bales can be stacked in up to 15 rows of a 3:2, 3:2:1 or a 4:3 arrangement. A bale should be unrolled along the top of the 3:2 and 4:3 arrangements to improve drainage.

Chaff or straw chopped one inch long can be piled on the ground, shaped and covered with a sheet of plastic. Such a pile can contain 42 tons (38 tonnes) of chopped straw or between 50 to 75 tons (45 to 68 tonnes) of chaff.

Covering the stacks

The stack can be covered in two ways. For large stacks of rectangular bales, it may be advisable to hoist the roll onto the stack, unroll the plastic along the top of the stack, and unfold it down the sides.

The other method is to open the plastic on the ground and drag it over the stack. The latter method is best for stacks of round bales or piles of chopped straw or chaff. If covering is performed on a day with no more than a light breeze blowing, three to five people can cover a stack in one hour. Assemble all the necessary materials and then wait for a suitable day, rather than trying to battle any appreciable amount of wind.

Place dirt or sandbags along one side once the plastic has been positioned over the stack. A small amount of dirt or a few sandbags are placed on the other side and rolled toward the stack by lifting up the edge of the plastic. This tightens the plastic snugly around the stack. The corners are then pulled out as if wrapping a parcel, and folded across the end of the stack. The entire cover should be well-sealed at the base of the stack.

Finally, all edges should be taped down (make sure that all loose edges are well sealed), and the stack should be covered with a fish net or camouflage net to reduce wind damage. The net can be tied to square bales or old tires to keep it in place.


Preparing and inserting ammonisation pipes. Use only iron pipes for adding ammonia to the straw or chaff. Iron pipes, about 22 feet (seven metres) long and 1.5 inches (3.8 cm) in diameter are sealed to a point at one end and threaded on the other. Screw a 1.5 inch by 1.5 inch by 1.0 inch (3.8 cm X 3.8 cm X 2.5 cm) "T" containing a four inch (10 cm) length of 1.5 inch (3.8 cm) pipe, threaded on both ends and capped, onto the end of the pipe. An iron adapter with a one inch (2.5 cm) male pipe thread on one end and a 1.75 inch (4.5 cm) male acme on the other is screwed into the "T," and fitted with a plastic cap. The 1.75 inch (4.5 cm) male acme will fit the valve on the ammonia hose. Beginning about two feet (0.5 metres) from the "T," drill 3/16-inch (0.5 c­m) holes every 16 inches (40 cm) along the length of the pipe on the side opposite the adapter. (See diagram below.)

The pipe is pushed into the stack with a tractor and adjusted so the holes point down, enabling the pipe to drain free of liquid ammonia. Insert the pipe until it is just past the hole nearest the "T."

Pipes should be inserted into both ends of bale stacks over 40 feet (12 metres) and half the ammonia added through each pipe. Because chaff piles are much denser, insert pipes every 10 to 12 feet (three to four metres) down the side of the chaff pile, and add a portion of ammonia in each place.

A plastic sleeve may help seal the plastic cover around the pipe in straw stacks, but is unnecessary in a chaff pile.

Determining how much ammonia to add

Add 3.5 per cent anhydrous ammonia based on the dry matter content of the stack or, if the stack contains 15 per cent moisture, you can add three per cent anhydrous ammonia based on the actual weight of the stack.

Example: 40 tons @ 15 per cent moisture X 2,000 lb. X 3 per cent = 2,400 lb. or 375 gallons of NH3 (40 tonnes @ 15 per cent moisture X 1,000 kg X 3 per cent = 1,200 kg or 1,880 litres of NH3.)

Adding the ammonia

Pressurized, liquid anhydrous ammonia is very hazardous. Chaff pile ammonisation should only be carried out by an experienced ammonia dealer. Before the ammonia is added, uncover a three-foot (one-metre) length of the plastic along the base of the stack, half way down one side. This allows air to escape from the enclosure as the ammonia evaporates. The opening must be resealed after or during the addition of ammonia if an excessive amount of ammonia begins to escape.

To avoid over- or under-application of ammonia to the straw, add the ammonia through a metered pump, and not from a nurse tank.

Removing the ammonisation pipe

About 20 to 30 minutes after all the ammonia has been added, the pipes can be withdrawn from the stack. Care must be taken to support each pipe as it emerges or it can damage the plastic cover. If It is necessary to hold the pipe, wear goggles and insulated rubber gloves for protection against any residual ammonia left in the pipe. The hole in the plastic cover should be sealed with two-inch (five-centimetre) plastic tape.

Uncovering stacks of ammoniated straw

The ammonisation process is complete in about 21 days. Leave the stack covered until a few days before the ammoniated straw is required for feed. When opening the stack, be careful to avoid exposure to the ammonia gas still present in the stack.

Open the stack on a day when there is a light breeze blowing away from buildings or corrals. If the plastic is not frozen, remove it carefully and you should be able to use it again as a cover with only minor repairs.

After the cover is removed, leave the stack for a few days to allow all the excess ammonia to evaporate; animals will not consume feed with a strong odour of ammonia. It may take a couple of days for the animals to get used to the smell.

Saskatchewan producers have had good success feeding ammoniated chaff stacked between two fences. When feed was required, the plastic was removed and electric wires placed at each end of the stack to control the animals.

Warning: Do not feed supplements containing urea with ammoniated residues. The combination may be toxic to animals.

Cost of ammonisation

The cost of treating straw with ammonia is dependent on the cost of materials.

Safety considerations

Be sure to observe all safety precautions noted.

Anhydrous ammonia is very toxic to the skin and eyes. If contact with anhydrous ammonia occurs, immediately flush it away with water or serious injury will result.

Liquid anhydrous ammonia evaporates, forming a gas with a pungent and disagreeable odour. Avoid exposure to the gas. Mixtures of 16 to 27 per cent ammonia in air can be flammable and even explosive.

As a safety precaution, never smoke or light a flame near ammonia.

Things to consider

The sooner a producer decides to ammoniate chaff or straw, the sooner he can acquire the necessary material and make arrangements for the treatment.

The earlier the treatment can be conducted in the fall, the better the results will be, since there is a better chance of having a higher ambient temperature. The chance of getting the ammonia delivered when required will also be much better if it is done before the fertilizing season begins.

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