Soil compaction vs Weight

[SCDolphin]

How much does a tractor have to weight before soil compaction is a problem? I want a tractor in 45-50 hp range which puts it without loaded tires at 3700 - 4000 lbs. Is that too heavy to a mow 5 - 15 acre field or even a smaller grass field?

 

[Birdhunter1]

Compaction is going to happen with anything of any weight. Ever see a 4 wheeler trail, cow path, horse trail, dirt road? It matters how much travel it gets in a confined space as much as it does the weight of the machine.
That being said if it is a field you are going to bushhog i wouldn't worry about it too much if you are just going for the grass only. I've seen lots of hayfields that don't get tilled at all for 10+ years that might have compaction but they produce good hay. I've seen crop fields that every 3-5 years need a deep ripper taken through them (especially at the headlands) but there you are talking about 20,000 lbs. macines (tractors, combines, semi truck's, spary rigs, etc) that especially during harvest time get lots of traffic (tractor with grain auger wagon or semi traffic).

Also depends on your soil type too and how much water getrs on it and how often.
If you want this 5-15 acres to be yard quality then a 500 lbs. machine may be a bit hard on the ground (compaction wise) but for a pasture type setting with good deep roots on the grass I wouldn't worry about it too much.

 

[john_bud]

Don't forget to factor in the tire type and size. Big ol turf tires will hardly leave a mark with a 8500# machine and skinny little ag tires will rip it up with a 3000#'er. Heck, WALKING across my fields after rototilling leaves deeper impressions than the tractor tires. Don't even get me started at the pock marks deer leave!

jb

 

[daTeacha]

Soil compaction is the subject of much research and discussion on a professional level. Basically, try to stay off the field unless it's dry, and minimize the amount of times you cross the same place.

There are two different theories used in European and American style agriculture, the Europeans going for a long narrow footprint and the Americans going with a shorter wider one. Studies of the actual compaction of the soil immediately under and to the sides of the area on which the tractor travels indicate the European idea gives less impact on the crops being grown on any given field. You may start seeing more and more tracked tractors rather than dual or triples on serious ag stuff as those studies are publicized and verified by other researchers.

 

[Pilot]

These guys have it right--Weight, tire type (contact surface area), soil type, soil moisture and number of trips are all important. Not mentioned is vibration. On construction sites, if they want to compact the soil they use a vibrating machine. So if you have a machine that vibrates while in use, make sure you run it when the soil is dry and minimize your passes over the same spot.

Regarding number of trips: Studies on Oregon forest soils showed that cats or low ground pressure skidders would compact the soil to the max in just 6 passes over the same spot.

Ground pressure: Typical ground pressures from logging equipment: Rubber tired skidders run around 12-15 psi, dozers about 6 psi and excavators 2-3 psi. I suspect that a farm tractor with ag tires would be in the same neighborhood as rubber tired skidders.

 

[daTeacha]

The tire manufacturers generally agree that the pressure on the soil under a tire is pretty close to the pressure in the tire plus 2 or 3 psi. Where the extra pressure comes from is something I don't quite get, but raising your tire pressure will increase the compaction you get even if you don't see any difference in how the tire sits on the ground. The lugs can deflect in toward the rim without it showing from the outside.

 

[KiotiJohn]

I've read numerous articles on the subject of lowering inflation to decrease compaction. This is a common practice and works well. It also has the side benefit of increasing traction.

Radial tires can operate with lower psi without damaging the tires than can bias plys.

John