Rain damage
Hay left in the field is vulnerable to rain damage. Given average drying conditions, slight moisture from dew or light rain should not hurt the hay crop. However, heavier rain spoils the crop, whether it is partly or fully cured, by leaching nutrients, compacting it, and encouraging microbial activity to mould and rot the cut material. Rotting windrows smother the crop regrowing beneath them, so they should not be allowed to lie in the paddock too long. Baled lucerne hay left in the field can suffer similar rain damage to curing hay.
When rain threatens the crop, hay is often baled too soon, which can lead to losses. Baled lucerne can dry out satisfactorily once shedded, provided the initial moisture content is not too high and bales are not tightly stacked together.
A reduction in bale compression reduces the risk of heating. Unfortunately, when these bales dry, they shrink from their binding and often fall apart on handling. However, this is probably preferable to losing a complete cut due to wet weather.
Respiration
Even after cutting the cells of plants they continue to respire until the plant moisture content falls to about 35% (65-70% dry matter). Respiration processes in the cut plants involve gradual using-up of valuable energy substances. This alone can result in loss of dry matter of up to 80/0 under good drying conditions and up to 150/0 under poor drying conditions. Respiration losses generally go unnoticed and cannot be avoided entirely. However, the most important practical means of reducing these losses is to cure hay as quickly as possible.
Dry/cure hay as quickly as possible by:
• mowing late morning, not late afternoon;
• mowing crops at the correct stage of development rather than when plants are more mature and coarse;
• leaving mown windrow as wide as possible;
• using a mower conditioner, which cracks plant stems, accelerating drying;
• using a hay rake to maintain the open structure of the windrow, especially in less than ideal drying weather.
Weather
Heavy rain on cut hay causes losses of up to 200/0 of the original crop by:
• leaching soluble energy substances from the hay;
• shattering the leaf, resulting in direct loss of protein and other nutrients;
• prolonging drying, therefore prolonging respiration as described above;
• creating a favourable environment in the windrow for mould by micro-organisms fungi, yeasts and bacteria.
Heat-induced
Commonly, losses of up to 10% of dry matter are incurred even in hay stored under cover at less than 200/0 moisture. This is largely due to handling losses. Baling hay at moisture content higher than 20% greatly increases the risk of spoilage by mould. If temperatures within the bale rise to 70°C as a result of microbial growth, studies reveal losses in digestible protein of up to 1000/0 and losses in energy of 40-700/0. (Simmons, K. and Sempendorfer, H., Dept Agric., Vic.).
Apart from the nutritional loss, a temperature above 70°C is regarded as dangerously high because if heat is trapped in the hay it could trigger a change from biological to a chemical heating that may cause a hay fire. Regularly monitor for thermal activity, which in closed storage areas may be accompanied by acrid fumes and sweating.
All freshly built stacks should be checked in the first two or three days after storing and then at gradually lengthening intervals for the next eight weeks, the main danger period. Old haystacks should also be checked regularly.
Better temperature monitoring can significantly reduce the risk of hay fires. Without using thermocouples, a common method of checking haystack temperature is to drive a steel rod into a suspected hotspot, leave it for several hours, then remove it and feel for the hottest spot along its length. Above 70°C the bar is too hot to touch. If the hay temperature continues to rise above 70°C the only solution is to make sure adequate fire-fighting equipment is on site, and then dismantle the stack.
A useful strategy for reducing the risk of overheating due to high-moisture bales is to reduce bale density (bale compression). This permits increased aeration and therefore cooling within the bale. This practice is often unsuitable for hay that is intended for sale, because it reduces the bale weight. Also, loosely compressed bales fall apart more easily, causing handling problems. In such instances, reducing bale length can help to make bales easier to handle efficiently.
Improving ventilation within, and around, over-moist baled haystacks is also a common strategy for reducing spoilage. Construct smaller stacks in a well-ventilated storage area and leave plenty of air space between bales, so that moisture and heat loss from bales is increased.
Mechanical
It is critical to minimise loss of leaf during haymaking processes, handling and storage. In lucerne, leaf accounts for about 500/0 of plant weight, yet the leaf contains approximately 700/0 of the protein, 900/0 of the carotene and vitamins, and more than 650/0 of the digestible energy. Nearly all mechanical losses are due to leaf shattering. Leaves dry down three to five times faster than stems and as the plant moisture reduces to below 300/0 the leaves become very brittle. It is therefore critical that baling takes place within the narrow moisture ranges shown in Table 8.1 on page 58.
Losses occur at every stage in the haymaking process. It is therefore necessary, in achieving top hay yields and quality, to reduce mechanical handling to the bare minimum.
Table 8.3 Losses of dry matter and leaves during haymaking operations
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