In between the bouts of unsettled weather that has marked June so far, there will be many anxiously awaiting the opportunity to get a hay crop cut, dried and in the shed.
With the weather being so catchy, it is important to make the most of what spells of sunshine do appear, and so it is worth giving some thought to the management of the sward as it dries.
An academic approach to tedding
Massey Ferguson has been doing just this in conjunction with Cornell University of New York State.
In a study which set out to look at the effects of tedder setting on swath spread and ground cover, it was found that both the rotor speed of a tedder and forward speed of the tractor, can have a significant effect on the way the crop is prepared for drying.
It is generally taken that exposing as much of the crop to the effects of solar radiation and wind will hasten moisture loss.
Swath characteristics
Therefore, it is important to obtain the ideal combination of spreading and stacking so as to gain the most from the heat of the sun and movement of air within the sward.
To this end, three characteristics of the tedded sward were measured, these were the swath width, the degree of ground cover and the height of the tedded swath.
These were examined in conjunction with two operating parameters, rotor (PTO) speed – 540rpm or 440rpm, and forward ground speed – 6.5km/h or 16km/h.
Width of spread
To obtain the greatest width of spread the optimum combination of rotor speed and ground speed was, surprisingly perhaps, found to be the slower rotor (440rpm) and faster ground speed (16.5km/h).
So is it better just to go fast when tedding? Not at all, for setting the PTO at 540rpm and heading off at 16km/h actually gave the the poorest result.
The rotor speed, when travelling at 6.5km/h, was nowhere near as critical to the spread width, but the final width at either rotor setting was still significantly less than the optimum settings.
Ground cover
Making the most of the field surface is obviously an important consideration, and the degree to which the amount of available area is covered should be closely allied to the spreading width, but this is not the case.
The best way to obtain optimum surface cover was found by going slowly with the PTO set at 440rpm.
The effect declined with the increasing speed of both parameters, the worst result being obtained at fast forward and rotor speeds.
The variation between the two approaches ranged from 85% at best, to 65% ground coverage at worst.
Tedded swath average height
Here the clear winner was a slow forward speed, the actual PTO speed made very little difference.
At 6.5km/h the average height of the swath was just over 15cm; at 16km/h it was just under 13cm, a clear difference of 2.5cm between the two.
An average figure, of course, hides any variation and when looking at the consistency of the swath, the real effect of the different operating parameters comes to the fore.
Once again the slower ground speed showed the least variation between PTO speeds, whereas at 16km/h, the slow rotor speed gave a far ‘lumpier’ swath than when the PTO was set at 540rpm.
It was not a minor matter either, the difference was over 5cm between the two PTO speeds at 16km/h, while at 6.5km/h, the difference was hardly noticeable.
A mixed bag from Massey Ferguson
There is little that is clear cut from these results. While they indicate the effect on the swath of altering two of the operating parameters, they do not give a clear picture of best tedding practice.
To give a more precise indication of the better overall strategy, we need to know what the effect was on the nutritive value of the preserved grass. Unfortunately, rain interfered with the trials and this decisive data was not recorded.
Despite this lack of conclusive evidence, the current advice of going fast on the first pass and then slowing down on subsequent treatments, would appear to be sound.
Possible tedding strategies
By tedding at the higher speed, the full width of the stubble left by the previous pass is likely to be covered, assuming that the mower was set to leave a guide line to be followed by the front wheel.
Having distributed the grass across the full width of cut, further tedding can concentrate on arranging the crop to meet three further criteria:
- Equal distribution across the field, best achieved by a slow rotor speed and reduced forward speed;
- A deep swath of uniform density, that density being as low as possible to allow the passage of air. A low ground speed is critical, PTO speed is more or less immaterial;
- Teasing out of the individual stems/leaves to avoid lumps and so discourage damp spots. Although not specifically assessed, this characteristic is closely associated with a low ground and PTO speed, ensuring the material is pulled at, rather than snatched.
Conditioning
Unfortunately, details of the methodology are not given, but it is probably fair to assume that the ryegrass sward was conditioned in this trial.
Conditioning is usually associated with breaking the stems and degrading the leaf cuticle, thus allowing the easier escape of moisture.
What is not so commonly considered is that conditioned grass does not pack as tightly in the swath, thus reducing the overall swath density throughout the drying period.
Tedding the cut crop should aim to build upon this characteristic of a conditioned swath; travelling fast in the second and subsequent passes is less likely to do so.
Further questions
This trial is a welcome reminder that there is a science as well as an art to making hay, yet there are many more questions to be answered.
The relationship between ground speed and rotor speed is shown to be a complex one, with some of the results being contraintuitive.
This suggests that a better understanding might lead to more efficient drying and nutrient preservation and poses the question as to whether tedder design can be improved upon.
Another major unknown is whether working the crop at different angles will have any effect on drying time.
By cutting across the lines in a swath, the crop is mixed, and it tends to fill in the gaps which are still present, or at least get the grass to lie on ground which may not have been previously covered.
Stubble length will also affect drying time as a longer stubble may aid ventilation while reducing the inclusion of the wet, and less nutritious, lower stem and leaf in the swath.
Machine development
This is the sort of research that is not quite as plentiful, or the results as freely available, as is desirable and Massey Ferguson is to be congratulated on taking this initiative.
It might well be asked as to what notice the company engineers are taking of the results and will we see future tedders with variable speed rotors, or a Tractor Implement Manager (TIM) capability which holds a tractors forward and PTO speeds at an optimal constant?
Swath management is something that has, so far, escaped the attention of the ‘digital-with-everything’ enthusiasts, that may be about to change.
