[Tim Harrigan]

There are many interesting aspects to this. In my way of thinking it is important to decompose the major issues in the fashion of peeling an onion. Inefficiencies exist in both systems. Engine-based systems have many inefficiencies but the productivity is greater. Animal-based systems have certain power delivery advantages but their engine is running 24/7. Certainly they can be integrated in other parts of the system, but this daily care and feeding responsibility was perhaps the biggest wedge that pushed horses out and let tractor power in. So while I really appreciate the energy and power delivery of draft animals I still think it is important to understand how energy use nets out. On an energy per board ft basis a low input system may have an advantage compared to a high input, higher productivity basis.

I am not exactly sure how to sort these things out without comparing two or more systems. It is sort of like the keyline plow question. If such a power intensive operation provides real and measureable benefits then they have to be real and measurable, not just a promise or a nice story. If you plow the entire field and things look better or worse the next year, was it because of the plowing? My pastures look different every year based largely on temperature, rainfall and rainfall distribution. If I split the pasture and plow only part, then I can see, measure and separate the plowing from the other environmental effects that I can not control. So I need to make objective comparisons to draw defensible conclusions. That’s the way I roll.

Now the ethical issues, environmental effects, renewable energy, those are deeper layers of the onion. Integral and important in a assessment of the entire system but different questions in my mind. If that is the way the assessment needs to go, that is fine, but if energy inefficiency or delivery is a component of a system I am trying to understand and you include it in your defense of a challenger system, my first question is ‘How inefficient is it? And compared to what?’

It is almost always harder to identify the specific question you want to answer than it is to actually answer it. In one of the classes I teach I tell the students to set field comparisons up to answer one question at a time. They do that by asking a question that includes the word ‘or’. Keyline plow or no plowing? Fifty lb/acre of compost N or no N? Do not ask ‘keyline plow and 50 lbs/acre compost N or no plowing?’ That question can be answered but it is more complicated and the separate effects still need to be unraveled. If you ask that question and measure or observe real effects you still do not know if the effect was the compost N or the plowing.

[Tim Harrigan]

The energy density (cal/gal) of diesel fuel can be determined from published values. Fuel consumption of forwarders and other machinery can be estimated based on fuel consumption per engine hp and likely fuel consumption rates can be estimated based on the Nebraska tractor tests. Energy use (cal) of horses can be based on feed intake. Good estimates of harvest productivity (bd-ft/h) will be needed for the horse-drawn system and whatever system it will be compared to. The comparison could be hp/bd-ft or cal/bd-ft delivered or whatever units of measure make sense. Hp output for the horses can be estimated based on reasonable and likely transport speeds and the size of the logs harvested. The calculations are not particularly difficult, a harder part is sizing and defining the nature of the systems to be compared.

[Tim Harrigan]

The hp unit was developed by James Watt in the late 18th century. He wanted to rate his steam engine in terms of the competition, the horse. After some tests he determined that a horse could lift 366 lbs of coal from a mine at a rate of 1 ft/sec or 22000 ft-lb/min. He increased it by 50% to 33000 ft-lb/min (550 ft-lb/sec) to underrate his steam engines. That has been the unit for hp ever since. A watt is now a unit of power. One hp is 756 watts.

[Tim Harrigan]

I would consider disking pasture or hay ground with straight gangs or slightly angled gangs to expose some soil to improve seed to soil contact for renovation, particularly for frost seeding. So the disking would be across the slope, late in fall to expose some soil. We typically would want to frost seed over a snow cover or on frozen ground so disking at that time would not be practical.

[Tim Harrigan]

I think tractor manufacturers are happy with machines that will pull (drawbar) their own weight (mass). 100% efficient. Nebraska tests are done on concrete and they measure pull in all gears, fuel consumption etc. Early tractors also introduced rotary power options, flywheel and pto that eased the transition. The lawn mower is a measure of rotary power and the hp is relatively high because of the high rpm, not particularly high torque.

[Tim Harrigan]

Good explanation Ben. Some of the tractor inefficiency could be even more than you mentioned. For instance, if you had 60 hp at the flywheel we would expect 50 at the pto and only 25 at the drawbar in sandy ground with a 2wd tractor. Like Ben said, it depends on the ability of the tires to maintain traction. On firm ground we would expect to make 39 hp at the drawbar.

Your estimates of peak pulling power are interesting and I haven’t given it much thought. It would be interesting to estimate it some time. It would be fairly easy to do at a pull if they were pulling a sled that maintained a constant load such as a stoneboat. For instance, to calculate the instantaneous hp if a team pulled a 10000 lb sled in a 6 ft pull. The calculation would be lbs force in the chain time speed (mph) and that product divided by 375 equal hp. So you would measure the travel speed of the sled with a stop watch in feet per second (6 feet in 3 seconds would be 2 ft/sec). Also, the force is not the weight of the sled but rather the force needed to move it. If on a firm clay surface I would guess 1/3 of the sled weight in the chain. So 10000 x .333 = 3300 lbs force. Multiply ft/sec x .628 to get mph. So HP = 10000 x .333 x 2 x .628 = 4182. 4182/375 = 11.15 hp.

Carl is perceptive in emphasizing that horsemanship is not captured in this measure of performance.

[Tim Harrigan]

I can help explain this but I will not have much time or energy for a few days. 🙁

[Tim Harrigan]

OK, I read the article that Carl posted. There is a lot of room for interesting discussion but I will not be able to add to it for a few days. One thing I like about these approaches is that they challenge us to think through the parameters of a balanced biological system and the most efficient way to achieve it. One thing we need to do is develop an attitude of experimentation and apply these types of treatments in defined areas where we can observe and measure the impacts compared to alternatives. If we till the entire field, or not till the entire field, how do you measure the value of what you did or did not do?

[Tim Harrigan]

Carl, FYI I have not been able to display either of those reference posts. Tim

[Tim Harrigan]

I have never measured the pulling force but I am familiar with that type of tillage tool. I would guess a horse-drawn, single shank keyline plow would pull in the range of 1000 to 1800 lbs force at 14 inches or so. So if you expect a team to work right along I would say at least three but probably 4-6 . It is really hard to say because soils can be so different and it depends on the nature of the restrictive layer that is to be disturbed. And how much lifting the plow is designed to do. Even a moldboard plow draft can vary by a factor of six to eight from sandy to clay soil, moist to dry etc. First, get a shovel and dig. Find out if deep compaction is really the problem. Deep compaction gets a lot of attention and in my estimation in a lot of cases is not the real source of the problem.

The role of such a tillage operation in building soil quality is debatable and is worthy of discussion.

[Tim Harrigan]

Not slugs, 🙁 oil seed radish suppresses sugar beet cyst nematodes and oriental mustard suppresses some soil borne fungal diseases like pythium and rhizoc. And the combination of manure and cover crops is more effective than either manure or a cover crop alone. 😀

[Tim Harrigan]

John: Here is a pdf of a presentation about some work I have been doing integrating manure and cover crops. This in not likely to be a draft animal application but you may find it interesting.

[Tim Harrigan]

John: Can you explain what you are doing and trying to accomplish with your pasture work?

[Tim Harrigan]

If you put something together let me know how it works. I have been doing some pasture and hayground renovation with a rolling aerator, not with animal power though. A disk tool in pasture ground have a lesser gang angle so would pull easier, but would need more weight for penetration. Might end up being about the same as our disk in tilled ground.

[Tim Harrigan]

John: It was actually a 23 tine harrow so probably for ease of recall think of 20 lbs per tooth at 2 inches, 30 lbs at 3 inches and 40 lbs per tooth at 4 inches. That is in disked soil.

I was looking back at some of my records of what others have reported with some of these tools. In 1917, Ohio State University professor Harry Ramsower published Farm Equipment and How to Use It. While not listing specific draft values, he described these spring-tooth harrows in common use: 2-horse harrow, 15-tooth, 4½ ft; 2- or 3-horse harrow, 17-tooth, 5½ ft; 3-horse harrow, 23-tooth, 7½ ft; 4-horse harrow, 25-tooth, 8½ ft. He did not indicate a depth of operation for the harrow. Although two horses handled our 23-tooth harrow at the shallow settings, three horses would have worked hard to pull it throughout the day at the deepest setting which averaged nearly 1000 lbs draft, quite a bit more that we would expect with a moldboard plow.

In 1931, Iowa State University professor J. Brownlee Davidson published tillage draft estimates for animal-drawn implements in a book titled Agricultural Machinery. A normal draft for a single-gang disk harrow was listed as 70 lbf per foot of width, but likely drafts ranged 50 lbf to 150 lbf per foot of width. The normal draft of 70 lbf per foot listed by Davidson was a good predictor of our disk harrow draft (72 lbf per foot). Our disk draft was 90 lb per foot with the added 160 lbs to increase depth of operations. The high-end draft of 150 lbf per foot seems quite high, but a heavy disk in soft soil could sink in and pull extremely hard.

Davidson listed a normal spring-tooth harrow draft of 75 lbf per foot of width, but likely drafts ranged from 25 lbf to 150 lbf. The normal draft of 75 lbf per foot is close to the draft we measured (83 lbf per foot) with the middle depth setting (notch 4, about three inches deep). The low-end draft of 25 lbf per foot is similar to what we measured (29 lbf per foot) when pulling the harrow without any tines in the ground. The high-end draft of 150 lbf per foot is greater than we measured in using notch 2 (4 inches, 131 lbf per foot), but it is probably pretty accurate since we could have increased tillage depth and draft by one more notch in the lever.

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