This article was written by Alex Barrie, OMAFRA Soil Management Engineer, and Ian McDonald, OMAFRA Crop Innovations Specialist
As discussed in the previous article (available here), as long as we are putting heavy implements on farm fields, soil compaction is a significant possibility. Lots of factors impact the severity of threat, like load, tire configurations (type, number, size), soil fitness and frequency of equipment passes.
We discussed how Central Tire Inflation Systems (CTIS) are a powerful tool in reducing the soil compaction threat. Eventually we may address soil compaction by eliminating or greatly reducing equipment load on soils by removing soil contact (Figure 1a) or greatly reducing the size of future farm equipment (Figure 1b).
In this article we will showcase reductions in soil compaction by employing CTIS. While many management options can be adopted to lower compaction threats, we have found that CTIS is one of the most effective, yet many farmers overlook its value. CTIS is not appropriate everywhere. It best fits on implements that are or carry high weight, do considerable road travel loaded and have significant frequency in the field. Things like sprayers, manure/fertilizer spreaders, hay and forage wagons, large square balers and self-propelled forage harvesters among others. While equipment like combines and grain buggies carry significant weight, they don’t tend to travel loaded on the road so their typical tire pressure is lower than their loaded weight would dictate for on the road and therefore less in need of CTIS.
Figure 2 shows different “rutting” of soil from a loaded self-propelled sprayer with wide tires on the left side and narrow tires on the right. Two passes were made: first with tire inflation at recommended pressure for road travel (35 psi) and second with the pressure for field travel (13 psi). Note that tire impressions in the soil with wide tires (2A) don’t appear to track the soil very deeply with either tire pressure compared to the deeper rutting with narrow tires (2B). This demonstrates that bigger tires with greater “contact patch” on the ground can distribute equipment weight over more area, reducing the likelihood and severity of compaction.
However, despite similar tire impressions (2A), data from field sensors still indicates that lowering in-field tire pressure, even with the wider tires, reduced weight stress from the sprayer (Figure 3). In the following sets of graphs, the response lines indicate the stress detected as pressure at the sensor depths of 6″, 12″ and 20″ as sprayer tires pass over. The horizontal lines represent the stress threshold values above which soil compaction is likely to happen in the topsoil and subsoil respectively. The lower the response lines the better. Left response curves are the front axle of the sprayer while right curves are the rear. Due to software issues, line colours are not consistent between graphs. In all cases the top response curve is for the 6″ depth sensor. The lines below are for the 12 and 20″ depths respectively.
Of note with results in Figures 4 vs 3, the tall narrow tire of Figure 4 has higher road and field pressures (50, 25 psi) compared to the wider tire (35,13 psi). This is a function of the tire volume and size. The narrow tire for the ground contact patch it can create has to be set at higher pressure to carry the load safely. Although CTIS with the narrow tire doesn’t reduce the compaction stress to the same extent as the wide tire, the differences between road and field pressure are significant (Figure 4). Despite the lower tire volume of the narrow tire, the benefit of the CTIS system is obvious.
In terms of optimizing with CTIS, many tire companies have yet to develop tire charts that reflect the pressure ratings for different tire types, speeds, loads, and field/road travel. It’s a work in progress but the sheer volume of tire options and concerns over tire liability means this continues to evolve. That said, many producers who know the limits of their equipment based on experience are making their own decisions for in-field tire pressures, and often operate even lower than what is published in tire charts. They understand the liability to these decisions but feel the benefits outweigh the risk to tire failure, although they are still very conscious of operator and equipment safety when setting field pressures. Remember that the stress on a tire operating in the field at lower speed and in straight lines is far less than on the road under load and higher speed. Many CTIS users are routinely achieving 5-8 thousand hours of tire life when they use CTIS, which goes a long way to paying for the system.
Another striking example of the value of CTIS is seen with manure spreaders. We looked at the huge Nuhn Quad system with 2 tankers and triple axles with 900/65R46 tires (Figure 5). Despite the massive load, very large tires reduce soil stress when compared to the self-propelled sprayer. For the loaded weight on the tanker tires, on-road pressure was required to be 40 psi but in-field pressure could be lowered to 10 psi. The difference in stress exerted to the ground was substantial (Figure 6).
Keep in mind for these two examples that equipment weight did not change. Reducing tire pressure from road to field travel allowed tires to “squat” without fear of failure and allowed the tire “footprint” to become longer, spreading weight across more ground area and lowering weight stress. This was discussed in the previous article (available here).
With or without CTIS, never operate a loaded piece of farm equipment on the road at speed where tires are not inflated to tire manufacturer recommendations. This is an absolute must from a road safety perspective!
While these examples have included large equipment, soil compaction also happens with smaller equipment. Soil compaction must be of concern regardless of equipment size and as such, CTIS likely has similar payback opportunity regardless of equipment size.
So, we encourage all producers to look seriously at CTIS. Its not for all applications but if you travel the road with loads that carry significant weights onto fields, optimizing tire pressure is critical to decreasing the potential and severity of soil compaction.