Orchard Groundcovers
There are a lot of different options out there for orchard ground preparation, and options for plants to establish in young and mature orchards. A lot of the information out there for establishing young pecan orchards isn't really geared towards really low input approaches.
For example, in some of my orchards (pictured below), conventional tillage before planting to 'prepare' a seedbed for ground cover establishment was not really a good option in my opinion for a few reasons:
1) Cost in terms of $$. When you start talking establishing acres of grass and legumes from bare ground seed costs start climbing quickly.
2) Cost in terms of soil erosion. Most of the trees are on extremely erodible ground, and I know these areas have lost enough topsoil in the past that I didn't want to lose more, so very minimal soil disturbance was a MUST
3) I already had some really desirable plant species growing in some of these areas and I would rather not kill them.
I could have went with some different approaches using herbicides. If I had wanted to use herbicides on this site, my best bet probably would have been to go from tree to tree and spray a wide circle of herbicide all around them. In my opinion spraying strips of herbicides within the entire row would not have been a good idea since some of these rows of wild pecan seedlings run downhill, so it is likely I would have suffered some erosion from that approach. Some areas are a fine silt loam and others are a sandy loam, and they have a tendency to erode the instant water moves over bare soil. So when thinking about orchard preparation in your own orchards pay attention to your unique conditions, because it is very likely some of the recommendations on 'best practices' for some locations may not work well for yours.
Working on so much highly erodible soil, I always try to prioritize protecting the soil. I can replace a lot of things, trees, others plants, etc, but I can't replace soil once it is gone. If I lose an inch of topsoil through carelessness, that is more soil than is going to be created in my entire lifetime.
In the end, what I chose to do in terms of ground cover establishment was extremely minimal and involved no herbicide or tillage.
So what did I end up doing in terms of orchard prep?
I thought about what I would need in the future for these trees. I wanted a ground cover that I could establish with minimal inputs (no tillage, no herbicide), and one that was going to work for me to help the trees meet the high demands for nutrients they will have in the future when they are trying to grow AND produce a nut crop. Since I knew these were two of the important things to me, I decided to look into legumes and combinations of legumes I could easily establish and that were most likely to persist (and/or set large amounts of seed) and continue to fix nitrogen into the soil for years to come. I decided to establish a mix of legumes, mostly through frost seeding (if you aren't familiar with this look it up). I bought bulk quantities of red clover, common white clover, ladino clover, and korean lespedeza and frost seeded them (after I inoculated them with the appropriate inoculant) for two winters over the entire area of the pecan orchards. The results have been excellent (see picture below).
ABOVE: Red clover and white clover are dense, the mowing early in establishment really helped.
ABOVE: You can see the prolific flowering of white clover across this field. Two years of frost seeding different types of white clover (among others) over this areas has really paid off. White clover seed especially is incredibly cheap per lb for the amount of seed you get. It also has a very low seeding rate because there are so many seeds per lb. It is also very effective at fixing nitrogen. It was a no brainer to include it in my mixtures. Note that frost seeding with clover was incredibly inexpensive for me. My total seed costs per year average out to something like $5 or so per acre, and my labor (it took a few hours to walk the whole pecan orchard using a hand broadcast seeder, but it worked very well for the extremely low seeding rate needed for things like white clover). I do not see any way to get that amount of nitrogen on these fields more efficiently and for such a long amount of time than what these plants are doing right now.
BELOW: This is a close up of what is going on. There are a lot of other plant species that are in the orchards as well, and that is fine with me. At this stage in the orchard I am not harvesting nuts from the ground so I don't need an orchard floor that is clipped very short to facilitate nut harvest. I can let the clovers, other legumes, and native plants grow relatively tall then mow them down a few times during the year. I try to time my mowing so that I am letting some of the clover and other select species go to seed if it is a species I want to see more of.
The moist winter of 2018-2019 and moist spring of 2019, coupled with regular mowing to control some of the grasses and other plants in the orchards, have allowed large numbers of the legumes to establish rapidly and make satisfactory growth this year. I have dug some samples of these legumes to check for nodulation on their roots (an indicator of below ground nitrogen fixation) and I am finding a large percentage of them with nodules. I am also favoring various native legumes including large areas of partridge pea (see picture below, really an attractive looking plant). When I mow I leave the large areas of partridge pea standing as it flowers, and allow it to go to seed. I have dug multiple partridge pea plants and I am seeing nodulation on their roots as well.
BELOW: Partridge pea on the edge of a field
BELOW: Nodules on a white clover plant
