Soil Is Key to Setting Up Trees for Success

Josh McGillAgriculture, Nutrition, Soil Improvement

By Brad Turner
Soil Is Key
An earthworm emerges from the root system of a recently planted tree

As I started my regenerative journey five years ago, it conjured up memories of walking the family groves in the 1970s with my freshly sharpened eye hoe. I would follow the tractor as it pulled the offset chopper, crisscrossing between the widely spaced trees in all directions. The native grasses and broadleaf plants — including legumes like beggarweed, crotalaria and hairy indigo — were laid down like a carpet ahead of me. Multitudes of insects filled the air and covered the ground.

My job was to hoe out vines, tall grasses and woody plants from around the tree that were too close to the trunk for the implement to reach. When I came to resets, I hoed them “clean.” Needing a break from the sweltering sun, I would lie on the cool ground in the shade of a massive tree. I can remember the sweet smell of the exposed earth where I had just uprooted huge lantana bushes from the base of a tree and witnessing the soil “move” with insects and earthworms.

I now know that both the smell and the movement of the soil were signs of a healthy soil. The smell indicated beneficial biology in abundance. The insects and earthworms served as shredders and decomposers, initiating the nutrient-cycling process and the future formation of stable humus.

Those hoeing and cross-chopping cultural practices that I experienced nearly 50 years ago have gone by the wayside. Though the citrus industry will not return to manually hoeing citrus trees, there are ways to manage our groves while promoting life in the soil.

From a soil-health perspective, getting a new grove planting off to a good start is much more challenging than transitioning an existing mature grove to more natural growing processes. Based on five years of study, trials at my research farm and collaboration with other regenerative growers, this article discusses some considerations concerning preparation, planting and establishing young tree health.

Diverse cover crops in a new planting can help build soil health

It takes many years to build stable organic matter in sandy soils. Mulches, quality compost, inoculums and biostimulants are valuable tools, especially in new plantings.

Rotations of multispecies cover crops in the middles and maintaining them as close to the trees as possible is the fastest way to build organic matter through the “liquid carbon pathway” via root exudates. This method can build stable humus 3 to 4 feet deep in Florida soils.

Integrating forage crops and intensively managing livestock on a field six to 24 months prior to tree setting will speed up the soil-building process exponentially.

Consider acquiring trees at least six months ahead of planting with the goal of building the trees’ immune systems and increasing leaf Brix to 12 degrees or greater prior to planting. The higher the leaf Brix, the more resistant the trees will be to larval and sucking insects. A scaled down citrus under protective screen system could be used. Consider:

  • Top dressing containers with vermicompost and/or inoculums
  • Adding fish hydrolysate and other biostimulants to the irrigation water
  • Applying specific nutrition based on regular sap analysis results

Establishing and maintaining low-growing cover crops beneath newly set trees is beneficial but challenging. Utilizing organic mulches is an option as well as water-permeable synthetic ground cover. If the latter is used, you will be mostly limited to liquid carbon inputs to feed the soil.

Block the rear discharge of your mower and cut a side discharge opening. Throw plant-available nutrients from the cover-cropped middles to the young tree drill.

Cover crops can be managed with paraquat herbicide

We all understand the financial advantages for early production. Yet, in high-density plantings, as tree canopies grow into each other, leaf volume is lost, and photosynthesis capability will decrease. This will affect the growth and health of the trees.

When backfilling the planting hole, combine 75% parent soil with 25% vermicompost or other high-quality compost. Ideally, backfill with topsoil shaved from the top 4 inches of the grove middle. This soil will have more beneficial and indigenous biology than the 12 inches of soil that has been extracted from the planting hole.

Mud-in trees, adding fish hydrolysate and diverse inoculums. Top dress with a trace mineral supplement.

Utilize regular sap analysis results to determine nutritional needs. Nutrition excesses have the potential to cause more problems than deficiencies. Prescribed foliar nutrition with added inoculums and biostimulants are necessary.

Use mineral fertilizer with predominately ammonium or urea nitrogen sources. Avoid excessive nitrates and muriates.

Small quantities of biostimulants and diverse inoculums need to be injected through the irrigation on a regular basis to feed and add needed soil biology.

Avoid excessive use of soluble nitrogen and phosphorous, which will short-circuit the biological system. Most fertilizers should be insoluble then made available through soil biology. A green tree is not necessarily a healthy tree. Painting a tree green with nitrogen can cover up other issues.

Soil Is Key
Cover-cropped middles with tree drill ready for mulch

With multispecies cover crops well established, overall pest populations will be reduced with beneficial insects outcompeting pests. Diaprepes and leafminers are proving to be the most challenging pests to keep in check.

There is always more to learn and research as challenges present themselves. Currently, I am trialing indigenous algae-eating protozoa to control algal spot.

Regenerative agriculture is not certified organics, meaning nothing is off limits. It is rather a process of achieving mineral balance and biological diversity in the soil and on the plant, with a focus on proper tree nutrition to optimize photosynthesis.

After combining a lifetime of growing conventional citrus, including commercial production experience and my ongoing regenerative research and experimentation, I have realized that I cannot grow healthy trees and profitable citrus the way I had for a generation. In this HLB era, it will take regenerative principles and soil-building processes to restore our soils to what they once were and put citrus greening in our rearview mirror.

Brad Turner is a citrus grower and operator of Sand to Soil Services in Lithia, Florida.