Regenerative Orchard Floor Management

Maximizing Photosynthesis: The #1 Soil Health Building Approach

By: Chuck Schembre, Understanding Ag, LLC

In the previous regenerative orchard blog, we discussed the connection between perennial crops and soil fungi, and introduced the importance of maximizing photosynthesis on the orchard floor.  It is important to understand that when soil fungi increase, so does the entire plant microbiome.  The function, health, and performance of a perennial crop is dependent on a healthy microbiome found on and within the plant, analogous to the importance of the human gut microbiome.

In this blog, I will begin linking regenerative principles to simple practices, which ultimately lead to increased photosynthesis throughout the year, which in turn lead to positive compounding effects to improving soil function, the farm ecosystem, and farm economics.

Maximum Photosynthesis on the Orchard Floor

Maximizing Photosynthesis is the main driver for rapidly improving soil health and ecosystem function on any farm.  Energy Flow is one of the ecosystem processes, and it can be also referred to as solar energy capture.  This requires promoting lots of vegetative cover, as long as possible throughout the year, with a diversity of plants.  I believe maximizing photosynthesis is so paramount in soil health education, we should be considering it as a soil health principle:  Maximizing hotosynthesis. 

Think about it for a moment.  Maximizing Living Roots, Maximizing Soil Armor, Maximizing Diversity, and Reducing Soil Disturbance (four of the Six Soil Health Principles), can only occur if photosynthesis is being maximized on the land.  This is why cover crops are so critical, and why it is critical in an orchard to allow vegetation to grow to a tall height and produce tremendous biomass at some point during the year.

Orchardists have been trained to keep the tree row strips clean and bare of vegetation, and keep the alleyways mowed tight to the ground.  Historically in the western U.S., the cultural soil management practices included full tillage in most orchard crops, or the blanket spraying of herbicides to terminate everything.  This is an all-or-nothing approach.  I sometimes receive a quick rebuttal when I teach about maximizing vegetation biomass in the orchard to conventional growers.  I am told, “There will be too much competition to the tree if you leave vegetation in the strip;” “There are too many rodents and voles will take the trees out;” “Insects will increase;”…and the list goes on.  So much fear has been engrained in the orchardist’s mind about vegetation, but the aggressive termination of vegetation and ground cover is likely the greatest contribution to so many of an orchardist’s problems.

The first process for anyone in the regenerative transition is to fully understand your farm’s context and how you can maximize the implementation of the soil health principles.  Maximizing vegetation, or photosynthesis, as much of the year as possible is the key.  If you have young vines or trees, do not allow too much vegetation near the base for too long, and allow the cover crop middles to put on great biomass.  If you have older, well-established trees, you can allow much more vegetation to proliferate.  I will outline specific management strategies in this article.

Managing Biomass to Promote Plant and Biodiversity

Introducing a wide range of plant species—grasses, legumes, and broadleaf plants—creates a dynamic system that supports diverse microbial populations. The organic matter from vegetation decomposes into the soil, feeding fungi and bacteria.  Improved soil microbial health leads to positive compounding effects including improving nutrient cycling, improving water infiltration and water retention at the same time, eventually leading to a reduction in disease and pest pressure. This is also referred to as ecosystem function.  Many orchard and vineyard diseases, such as phytophthora are created or exacerbated by agricultural practices which have created dysfunctional soils. Plain and simple, dysfunctional soils promote more disease and create conditions for common pests.  Once the 6-3-4Ô principles are implemented intentionally after three years (give or take), we generally see a huge reduction or complete elimination of common agricultural diseases.

Fundamental Practices to Support the 6-3-4 Framework:

Maintain Plant Residues and Litter: Leave at least 50% or 6-inch stubble of the above-ground vegetation intact in the alleyways to continue feeding soil biology and armoring the soil.  We also need to capture and decompose the tree leaf litter in place, near the tree base.  Leaf litter and small wood builds the duff around the tree which is critical for tree health. Many orchard floor sanitation practices prevent the organic buildup of duff, and these practices are actually contributing to the disease problems, by never allowing the beneficial saprophytic fungi to flourish.  This advice is contrary to the conventional approach.  Conventional farming wisdom states that the “leaf litter is harboring and contributing to the disease pathogen load of the orchard.”  However, the duff supports beneficial saprophytic fungi which is one of nature’s most powerful tools for reducing disease pathogens.  General university recommendations include blowing or sweeping the leaf litter out from under the tree row, shredding it, and even applying up to 40 lbs of N as Urea to break it down. Orchard floor sanitation practices are known to cost anywhere between $100-200 per acre depending on the crop.  Eliminating this practice means more easy savings in the bank account, not to mention an eventual decrease in pesticide application.

Managing the Tree Row Berm

This is the greatest challenge for management.  How to manage for good soil health in the tree or vine row?  If the trees are young, say less than five yrs old, do not allow the “weeds” to become dense and tall.  Period.  And, of course, rodent habitat can be a serious issue.  But also understand, “Roots Fix Soil” (a quote from Rick Haney, Ph.D.).  I like to say it another way, “Roots Build Biology.”  You have to find periods of time within the year to promote decent vegetation biomass near the tree.  It does not have to be all or nothing.  Reduce disturbances and increase soil armor.  With my clients and in my own farming, I have found many strategies to accomplish this without any devigor to trees or vines.

High-density plantings certainly pose more challenges with the shallow, less robust root system, and tight spacing between each tree.  However, when trees are well established and especially older trees on mid- to low-density planting, you can allow plenty of vegetation around the tree.  I have witnessed trees “perking” back up, and we have fixed nutritional issues in trees by establishing more vegetation.  It can go both ways.  Too much competition of vegetation is bad, but little or no vegetation is potentially worse.  Let’s be honest, the majority of orchard tree rows are dead soils, compacted, sealed soil surfaces, and are not cycling nutrients.  And if you are a nay-sayer, or fearful of promoting more vegetation, I ask you this:Is a little vegetation scaring you more than the dead, compacted soil your cash crop is growing in?

Examples of a typical orchard tree row berm, devoid of vegetation with excessive bare ground. The soil is very compacted, devoid of soil life, and has turned into “concrete”. The image on the right illustrates very poor water infiltration during a field water infiltration test.

Herbicide Reduction

Herbicides, especially systemic and pre-emergent chemistries, harm soil fungi and sterilize the seed bank. Glyphosate is well known to lock up important soil minerals and nutrients, reducing the ability of the soil to cycle and make these nutrients available.  We suspect many other herbicides could have a similar effect, but these have not been as scrutinized as glyphosate.  What we do know is the routine application of herbicides applied to the tree row creates a soil “dead zone,”  wherein the dysfunctional soil is not providing much in the way of nutrients.  Interestingly, this is where we farm our cash crop…in the most dysfunctional soil. 

Well-established trees and vines can handle a fair amount of vegetation growing around or near the base, without causing yield reductions.  In some cases, the soil is so compacted and dead, allowing native vegetation to grow immediately can improve tree health.  The vegetation or “weeds” still need to be managed and not allowed to suffocate the tree.  However, allowing vegetation to populate around the tree or vine during an extended period of the year (at least 4-6 months) improves soil function.

Simple Herbicide Reduction Strategies:

• The tree or vine row does not have to be completely bare.  Bare soil = dead soil.  It is important to shift the mind set away from the “all or nothing” approach.  Allow vegetation to populate the tree row.  Remember, a living root in the soil is paramount, and plant roots fix soil.  We need to allow some vegetation to grow.
• Narrow the herbicide spray strips.  In many orchards, the sprayed strips constitute 40-50% of the total ground surface area.  Especially in newly planted orchards, there is no need for a wide strip.  A young plant only needs a small area around the base free of weeds to reduce competition.
• Eliminate pre-emergent and systemic herbicides entirely.  Pre-emergent herbicides are great at what they are designed to do, which is stop anything from growing.  Systemic herbicides, like glyphosate are generally non-selective to all living organisms, will greatly impact soil biology, and reduce available nutrients.  
• Reduce the number of herbicide applications.  The tree or vine row does not have to be completely bare.  It should not be all or nothing.  It is practical to get away with one herbicide spray to control and knock back the vegetation.  Aim for one herbicide application and apply it as late as possible in the season, within your context.
• Utilize contact herbicides to knock back and control weeds.  Contact herbicides will allow vegetation to grow back.
• Alternate herbicide chemistries. Ideally, eliminate per-emergent and systemic herbicides, but if things are out of control, low rates may be used in alternating years.  Herbicide plant resistance should not be an issue if herbicides are not routinely sprayed at full rate. 
• Add a biostimulant.  If applying herbicides, consider adding a biostimulant of some type to help reduce adverse impacts to the soil microbes.  It has been shown that adding a biostimulant, such as a humic acid, yucca, or molasses allows for reducing the herbicide rate, while maintaining and or improving the herbicide efficacy.
• By applying some of these techniques above, we have found an immediate cost reduction of $50/acre on average.

Eliminate Herbicides – Organic Weed Management

This topic and recommended strategies likely require an entire blog, but I will keep it somewhat brief as a discussion point here.  Eliminating herbicides and taking an organic weed management approach will result in better soil health, but this comes with a lot of additional expenses and equipment investments.  The effectiveness of an organic approach is entirely context dependent, and these variables include the annual rainfall, soil type, age of tree or vine, rootstock and plant spacing, and premium for the product being grown.  A multi-pronged approach is required, especially if farming brand new trees or vines organically.  Here are some tips:

• Organic herbicides – There are some good organic herbicides on the market and this industry is about to greatly improve.  They will not provide full control, but when applied at the right time with good coverage, they will provide one step in the control.
• In-row mowers – Many companies have developed and advanced in-row mowers, and the technology has greatly improved.  They are expensive, but are highly effective in well established orchards as the singular weed control.  I prefer mowers over in row cultivation equipment because the soil is not tilled and disturb. 
• Side-mulching mowers – more companies are developing flail mowers which can discharge the cover crop cuttings out the sides into the tree row, increasing mulch material.  Mowing generally has to occur at some point, so it is a win-win.  The clippings will not suppress weeds alone, but will add another tool in their management.
• Mulch – Thick applications of woody mulch, preferable mulch that has gone though some decomposition is ideal. Mulch alone will not suppress weeds, but will help in year one.  The mulch also adds food for fungi.
• Young trees and vines – It is critical to invest in good grow tubes which can prevent rodents such as voles and field mice from girdling.  You will likely have more vegetation near the new plants, so invest up front in protection.

Last Thoughts

There are many other practices to discuss, and one of the most powerful vegetation biomass tools is livestock integration.  In the next blog series, I will examine Adaptive Grazing principles for orchards and vineyards.  Livestock integration is not mandatory to begin improving soil health and creating a strong regenerative farm, but it is a powerful tool which can get us there much faster.