Silage Insights - Research
When to handle round bales after stretch film is applied

By Dr. Rolf Spörndly, Rainer Nylund and Torsten Hörndahl Swedish University of Agricultural Sciences, and Per-Anders Algerbo, Hushållningssällskapet Malmöhus

A project financed by the Swedish Farmers' Foundation for Agricultural Research

Background
It is becoming more common to press and wrap round bales on the field using a combined baler and wrapper machine. The discussion has been intense among farmers and contractors on when the bales should be removed from the field for storage. The Swedish University of Agricultural Sciences (SLU) has conducted a research project to provide a scientific view on this open question.

The most common method in Sweden today is to transport the bales on a wagon to the farm for storage under bird netting. The loading and unloading of the wagon is done by a bale grip mounted on the front loader at the tractor. However, among farmers and contractors, there is a widespread belief is that the handling of the bales cannot be done at any time. It has either to be done within a few hours after the wrapping and before the lamination of the film layers takes place, or after a week when the lamination is completed and no more gas is produced in the bale.  These convictions however could not be supported by research data or controlled experiment.

The study
The study conducted by the SLU comprised of 70 round bales made from clover/grass crop harvested in the first and second cut in southern Sweden. The crop was pre wilted to 43% Dry Matter (DM) in the first cut and to 75% DM in the second cut. No silage additive was used. The bales were pressed and wrapped using a combined baler and wrapper machine, a Vicon RV 1601 Combibale (flex chamber). The wrapped bales were handled with a Trima Quadrogrip at five different intervals. One treatment had no gripping at all, while the other treatments involved handling with the bale gripper after 1 hour, 3-5 hours, 24 hours, 3 days and 10 days from wrapping.

Measurements of bale tightness were made on two occasions. The first at six weeks after wrapping and the second just before opening which occurred nineteen weeks after wrapping for bales harvested in the first cut and thirteen weeks after wrapping in the second cut. The tightness was described as the time for an applied compression of -200 Pascal (Pa) (vacuum) to rise to -150 Pa. The compression was produced by a pump prior to measurement. As a complement to the tightness measurement the degree of visible surface yeast and mould was noted at the opening of the bales.

Results
Table 1 - Tightness and prevalence of yeast and mould. LSM (least square mean) over 2 cuts.

	DM (Dry Matter)	pH (basicity)	Am-N, % of cp (Ammonia % of crude protein)	Tightness occasion 1 seconds	Tightness occasion  2 seconds	Yeast %	Mould %
Cut 1	42,3	4,7	9,9	1144*	541*	0,01	0,17
Cut 2	75,7	5,6	1,6	1312*	662*	0,05	0,65
Sign. diff	<0,0001	<0,0001	<0,001	n.s.	n.s.	n.s.	<0,01

Treatment	Tightness occasion 1 seconds	Tightness occasion 2 seconds	Yeast %	Mould %
Not handled	1333*	354ab	0,15a	0,64
1h	1212*	606ac*	0,00b	0,39
3-5h	1493*	986c*	0,01ab	0,46
24h	1323*	611ac*	0,00b	0,24
3 days	1238*	650ac*	0,00b	0,15
10 days	769*	402ab	0,00b	0,54

Notes:
Numbers with * differ significantly from the value 100 seconds, p<0,05
Numbers with the same column with no letter in common differ significantly at p<0,05

Fig. 1 - Tightness of bales handled at different times after wrapping

Notes:
"Tightness 1" is measured 6 weeks after handling and "Tightness 2" is measured 13-19 weeks after wrapping. LSM (least square mean) two cuts.

Fig. 2 - Mould and yeast on bale surface at the second cut

Notes:
"Tightness 1" is measured 6 weeks after handling and "Tightness 2" is measured 13-19 weeks after wrapping.

Conclusions

• The hypothesis that bales are more vulnerable to handling in the 3-5 hours until 24 hours period after wrapping can be discarded. Results indicate that bales are actually more resistant during this lapse of time. Bales with the lowest tightness and the few bales that broke at handling were all found to be outside this time limit.
• Bales not handled at all and bales handled on day 10 were overall the least tight.
• The experiment highlights the importance of the power used for gripping. Using too high power makes the bales crack.  The appropriate power certainly depends on the type of bale grip used, but this could not be studied in comprehensively in this experiment.

As general conclusion one can affirm that the time when a round bale is handled is not important. It is however recommended that bales should be transported to its storage as soon as possible within the first day from wrapping. With respect to the exposure to handling, the transportation could actually be done at a later stage, but in order to protect the bales from birds and rodents it is not recommended to leave them on the field longer than necessary from a logistical point of view.

Dr. Rolf Spörndly is research leader at the Swedish University of Agricultural Sciences in Uppsala and Chief advisor at Svenska Husdjur, a farmer's cooperative company for advisory services to dairy farmers. Rainer Nylund is research technician at the Swedish university of Agricultural Sciences, Uppsala. Torsten Hörndahl, is a teacher at the Swedish university of Agricultural Sciences, Alnarp Per-Anders Algerbo is advisor at the Hushållningssällskapet Malmöhus, Malmö

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