“Wilted silage, ideally, should be in the pit or bale within 24 – 36 hours of mowing,” says Frank Mickan, Pasture and Fodder Conservation Specialist, NRE, Ellinbank. The longer the cut pasture or crop is wilted on the ground before harvesting, the larger the losses in quality (energy and protein) and dry matter. Also greater is the risk of the next shower of rain resulting in even higher losses.
Good quality silage will be over 9.8 Megajoules of Energy per kilogram Dry Matter (MJ ME/kg DM) and will produce rapid growth rates in beef cattle or extra milk in lactating cows. To achieve this quality pasture is usually cut 2 – 5 weeks before you would normally be cutting hay in most areas. There are a few exceptions to this rough guide such as lucerne, sub clover, vetch and maize crops. This means that you will be harvesting when the ground is moist, the weather is cool – warm only, and may even be overcast.
How can harvesting be achieved in these circumstances? Sometimes it won’t be, but there are a few management tips and machines now more readily available that can make this possible. Harvesting high quality crops early in the season can be achieved by:
- cutting lighter crops.
- allowing the dew to lift before mowing and subsequent treatments.
- mowing with a mower conditioner.
- mowing with a mower conditioner but leaving a wide swath.
- spreading/tedding immediately after mowing.
Harvesting early in the season often means cutting lighter crops (stubby bottle to beer bottle height) which will dry quicker than if cut at the stage most crops are harvested (1.5 – 2 beer bottle heights). Although yields will be down, quality will be up dramatically. Lighter swaths will take up more moisture overnight than heavy swaths but will lose it faster the next day.
Mower conditioners are making a comeback and incorporate a wide range of conditioning techniques. The tyned and brush types are most suited to pastures, younger lucernes, clovers and vegetative cereal crops while the roller types are more suited to the stemmier type crops such as cereals cut with a seed head, summer forages (eg. sorghum) and mature lucernes. However the operator’s experience and conscience to do the correct job, the speed of the operation, the correct setting up and maintenance of the machinery, etc. can see an overlap of the categories above.
Plant stomata, the thousand of holes per square centimeter through which the water moves in/out of the plant, close within 1 – 2 hours of mowing, depending on climatic conditions. This reduces the rate of drying and prolongs the wilting period.
Tedding or spreading straight after mowing will promote increased water loss via the open stomata by an extra 50 – 80% for a few hours. Tedders are machines which operate, usually in a horizontal plane, to spread the mown swath so that all ground is covered and the plants are left more “teased up” into the air than if mown only. Some bruising of plants will also occur at the same time promoting faster water loss.
Table 1 shows the results on an experiment in Ireland which compared different types of swath, and conditioning or spreading versus no drying treatment. A perennial ryegrass crop, very wet at mowing (13.3 % DM) and 30 tonne/ha fresh weight (about 4200 kg DM/ha) was harvesting under dry weather conditions. The windrows were left as a single (single swath) windrow, left side by side (double swath) or spread after mowing(spread). Dry matter content of each windrow was measured 8 and 32 hours after mowing.
Treatment Unconditioned Conditioned
8hrs 32hrs (32hrs) 8hrs 32hrs (32hrs)
Double 15.6 18.2 (20) 16.1 19.3 (22)
Single 18.3 24.6 (29) 19.4 27.3 (33)
* Note.The figures in brackets are my estimates of what the dry matter contents might have been under Australia’s much more favourable wilting conditions.
Regardless of the climatic conditions , crop size, etc. many other experiments have verified the above order of increase in drying rate for pastures.