The root of tree health is fertility, and fertility begins in the soil. Simply amending the soil or using a foliar spray each season isn’t the answer to orchard fertility; these are merely tools used to address concerns.
“Nutrition needs to be something that we do every day, not just once or twice a year,” said Mike Biltonen, pomologist and founder of the ag consulting firm, Know Your Roots.
“How can we manage the orchard and the trees for better health?” is the question. Soil fertility is the answer.
“Soil isn’t just the physical thing that holds nutrients and water in place,” Biltonen said. “Soil is the real foundation of plant health.” In many orchards, the grower must “continually apply amendments” to keep trees productive, because soil nutrient levels are not adequate.
Not only does this approach repeatedly require time and money, it doesn’t do anything to improve the health of the soil ecosystem. Building and maintaining a healthy soil ecosystem will protect the long-term health of the trees, enhance the quality of the fruit, decrease disease and pest pressures and keep trees in optimal production longer.
A basic soil test is a good place to start. But it isn’t just the level of soil nutrients that matter. Stored nutrient banks are important, too. Unavailable nutrients — those “bonded in the soil” — cannot be utilized by the trees. Ph and cation exchange capacity (CEC), the total capacity of a soil to hold exchangeable cations, play roles in nutrient availability, as do microbes.
The three-dimensional picture of soil health includes physical, chemical and biological properties. To thrive, soil must not be compacted, and it has to have good water infiltration, contain readily available nutrients, have a stored nutrient bank and support a thriving, beneficial microbial community. Trees are healthiest when there is a strong soil fungal community.
Penetrometer readings to record surface and subsurface compaction are a good tool. Soil respiration tests will help determine the amount of microbial activity and soil organic matter. Counting earthworms — the goal is 10 to 12 worms per shovelful of soil — is a good indicator of overall soil health.
“We can grow apples like there is no tomorrow,” Biltonen said. “But can we keep the orchard alive long enough to do what it really needs to do?”
If establishing a new orchard, working with the land for a year or two before any planting commences is recommended to build healthy soils. This approach offers the best opportunity to “decompact the soil at all levels,” he said.
Cover crops will enhance fertility, improve physical properties and help establish positive soil biology. A spring mustard crop can serve as a biofumigant. Sudangrass planted in the summer will compete with weeds and provide nutrients when tilled into the soil. A daikon radish and field pea mix in the early fall can go dormant in the winter, and possibly regrow in the spring, providing cover and nutrients, decrease compaction and be terminated before planting. These methods increase the soil organic matter, too, which is an important component of ongoing soil health.
Enhancing soil health means moving beyond the standard soil or foliar applications of nitrogen and potassium.
Typically, orchardists focus on these levels but often don’t pay enough attention to the availability of other nutrients, and tree health suffers.
Trees with increased pathogen pressures are probably suffering from soil health concerns. As fertility is built, pest and disease pressures can decrease dramatically, so establishing true soil health will decrease the need for foliar sprays.
Adding nutrients via foliar sprays is “like taking vitamins” and is a quick way to get nutrients into the tree to help it along, Biltonen said.
In a mature orchard setting, deep incorporation of nutrients within tree rows is not possible. The most common orchard management practice is herbicide strips within the tree rows and grass between rows. This practice, however, does not encourage soil health.
Soil biodiversity is a key component of soil health and enhancing it within the mature orchard is possible. Taking that grass strip and altering mowing patterns is a good place to start. Simply allowing the grass to grow can provide insect habitat.
Increasing biodiversity will give growers a “much better chance of having an orchard system that is going to be healthy every single day,” Biltonen said.
Adding a cover crop to the grass mix between rows can enhance pollinator presence, increase beneficial insect habitat and help with soil fertility. Mowing so that the cut vegetation is thrown into the tree row, providing organic mulch, and adding organic matter and nitrogen will enhance soil health.
Utilizing a mulch of wood chips within the tree rows will provide carbon. When combined with chicken manure for nitrogen, it will ultimately act as a “slow release fertilizer.”
Water and fertility
Availability of water also impacts soil health. Microbes cannot migrate over dry terrain, so less than adequate soil moisture will negatively impact soil biology. Trees cannot take up enough nutrients without adequate water, and plant health will decrease as trees become stressed, leading to pest and disease issues.
In high-density situations, the very dwarfing root system is about one-third the size of M7 rootstocks, and the roots are all found on the soil’s surface. This means extra attention to proper watering is prudent. With tools available for soil moisture monitoring, all growers should be monitoring their soil water needs and irrigating as necessary.
Whether the orchard is planted in a high-density system or not, “growers are not managing their irrigation properly,” Biltonen said. Without a minimum of one inch of rain per week, the orchard will be under stress. Add runoff and evapotranspiration losses, plus any water going to weeds, and the actual water available to trees is probably less than the grower realizes.
“The tree needs water to be able to cool itself,” and will draw water from the fruits if needed to do so. Inadequate soil moisture has a “cascade effect” resulting in reduction of fruit quality and affects overall tree health and soil fertility, he said.
Perennial crops require a long-term commitment. Meeting their fertility requirements is best accomplished by building a healthy soil ecosystem from which the trees can obtain all the needed nutrients to thrive.
Whether you’ve got mature trees, young trees, or are planting a new orchard, focusing on soil fertility will enhance fruit quality and decrease pest and disease concerns.