fence - Why does USDA require wooden posts when ...

I've fenced off an area near our house to make an off-leash play area for our dogs.

I used T-posts and 2" x 4" (cell size) net ("utility fabric") from OKBrand.com:

On the other side of that piece of paper is a link to "installation practices" document from the USDA Natural Resources Conservation Service, https://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs144p2_016391.pdf which states:

Steel posts must be new and be painted or galvanized and weigh a minimum of 1.25 pounds per one foot of length. Post will be driven 18” inches in the ground or as specified by manufacturer. Every 50 feet or 4th post will be wooden.

My fence is 50 feet by 30 feet -- and it's 100% T-posts.

I was wondering WHY they say that there should be wooden posts mixed in with the steel ones?

Is there a practical reason to mix in the wooden posts?

Metal T-posts rank among the most versatile and useful items for any farmer to have on hand, which is why you’ll probably want to have dozens of them at your disposal. These tough metal stakes, which come in various sizes, are small enough to easily install and remove from the ground but hold their position well. They can be used for a wide variety of farming projects.

Coming from someone with a lot (and I mean a lot) of experience using metal T-posts, here are just a few of the ways that they can come in handy on the farm.

Building Fences

Certainly one of the main uses for T-posts is in fence construction, as they make excellent posts and are easy to use. All sorts of wire fencing, including mesh wire and electric wire, can be used in combination with T-posts; in fact, I constructed a mesh garden fence earlier this year that has proven very effective at keeping deer from munching on vegetables.

Supporting Fruit Tree Branches

Sometimes fruit trees can become so eager to grow an abundant crop of large fruit that they produce more than their branches can handle, with the weight of the fruit causing the branches to droop severely or even break. Placing a T-post underneath a troubled branch can give it a boost and help protect it from damage. Even if it has already suffered a crack, you might be able to save the branch by using a T-post for extra support.

Building A Trellis

Looking for a way to support climbing plants such as peas, beans or grapes? You can use T-posts as the anchor posts for simple trellises, running mesh or wires from post to post to provide handholds for the tiny tendrils of these climbing vines. Case in point—I built a simple T-post trellis for some old grape vines earlier this year, and they’ve been thriving all summer.

Marking Hidden Obstacles

Remember that giant rock jutting out in the middle of your hay field? It might be easy to find in the spring when the grass isn’t growing, but in the middle of summer, finding that rock (and avoiding it with your machinery) can be a challenge. That’s why it can be wise to use T-posts to mark the locations of such hidden obstacles, providing a clear visual reminder of the objects’ whereabouts so you don’t have to worry about hitting them and damaging your machines.

Anchoring Trees In The Wind

Planning to plant a row of young trees in a windy area of your farm? If they’re small and spindly, it could be difficult for them to stand up in the face of strong winds. But fortunately, you can anchor them in place by tying them to T-posts, which will provide extra support during their formative years and help protect them from damage.

What are some of the ways that you use T-posts on your farm?