Animal forage must be properly dried for storage so as to prevent decay and a loss of nutritional value. Depending on the conditions in which it is grown, the moisture content may vary from 75% to 80%. This is reduced to 60-65% for haylage and to 14-18% for hay, with lower moisture being required for larger bales.

With increased labour costs and markets that demand higher quality products, mechanical systems for hay drying become progressively more viable. Mechanical drying helps to minimize leaf loss and forage losses due to rain and removes the fire hazard associated with spontaneous combustion of the hay. Most mechanical systems use unheated, fan-assisted drying systems with ducted air distribution systems.

The ideal drying system takes several factors into consideration, including the capital and operating costs, the installation space, the required airflow rate, ease of use and the pressure losses which will occur. Choosing an incorrectly sized fan can result in higher costs or poor performance. The relative amount of different types of vegetation in the forage and its initial moisture content will determine the amount of airflow that is needed, and consequently have a considerable impact on operating cost. As a rule of thumb, 160 litres of air per second per tonne of forage will be needed for hay with an initial moisture content of 25-30%. As little as half this figure may be needed for forage that is initially dryer. Drying hay with an initial moisture content above than 30% artificially is relatively risky.

Fans are typically selected to handle a static pressure of 0.25 kPa. Centrifugal fans are usually more expensive, but can handle higher pressures and may be quieter.

It is often preferable to equip the drying system with several fans. Where possible, fans should be housed in such a way that the motor heat can be applied for drying to save energy. Automatic control of humidity and temperature and a timer will increase the reliability of the system and make it easier to operate.

Care is required with the air distribution system, as poor work on ducting will lead to pressure losses, lower efficiency and slow drying.

CFW has extensive experience in providing air equipment to the agricultural industry. We have undertaken many turnkey drying projects at various scales.

Lucerne is an important source of hay for animal feed and can improve rumen health in cud-chewing animals. It is especially useful for milk-producing animals (mainly cattle and goats), but also feeds sheep, horses, rabbits and camels. The modern alfalfa-drying industry is a competitive one in which energy efficiency and blending to fulfil the needs of different customers are key factors.

Green alfalfa is dehydrated in several stages. The crop is conditioned (i.e. the stems are crushed or crimped) and pre-dried in the fields. There is some disagreement about what the internal moisture should be before further processing, but 20-40% is sometimes cited. It is then usually chopped and continuously introduced into one end of a rotary drier – essentially a horizontal cylinder or drum through which hot air is passed, drying the hay. The cascading of the material as the drum turns ensures more uniform drying.

The leaves pass through the dryer faster as they are lighter and contain less moisture, while the stems take longer to dry. The dehydration process does not affect the nutritional value of the lucerne as far as caloric and protein content is concerned, although it may slightly decrease its digestibility. Proteins remain absorbable and intact up to at least 100 °C, and serious damage to the protein in leaves occurs only at around 200 °C. The problem of case-drying also does not affect alfalfa, making it possible to dry it at high temperatures.

Some research indicates that a recirculating heat pump dryer may be more cost-effective and reduce drying times, low energy consumption being a key consideration in the forage production industry. The final moisture content for further processing should be in the region of 6-12%.

Often, the dried alfalfa is processed into pellets after this drying process for easier storage and packing. The dried product is pneumatically conveyed to a cyclone to separate it from the hot water vapour in the exhaust. It is then ground in a hammermill and passed through another cyclone to in which the meal is collected. The meal is steam conditioned and sent through an extruder which produces pellets which are then cooled. Whether the final product has long or short fibres, or granules, also affects its digestibility.

Compared to natural drying into hay, mechanical drying leads to a smaller loss of nutritional value (especially with regard to vitamin A loss), reduces the risk of bacterial contamination and makes for greater evenness and control in the process. This is because anti-nutrients in the fresh lucerne are destroyed and the drying time is reduced. In short, high-quality forage can be produced without regard for fluctuating weather conditions.

A mechanical dryer is non-negotiable where large round bales of alfalfa are to be produced, since losses due to sun and rain may be unacceptable if natural drying is relied on. With larger land areas devoted to alfalfa, this drying method becomes more economically attractive.

The production of large amounts of high-quality alfalfa, often a profitable enterprise, has been the main reason for the practice of using artificial drying systems. Market expectations focus on low leaf loss, the absence of mold, good colour and high protein content.