Organic Orchard Management: Nutrition for Organic Orchards
|Fertilizer||Comments||Pros and Cons|
|Alfalfa meal (pellets)||Primarily used to increase organic matter in soil, but also offers nutrients and a high availability of trace minerals.||
pro: Available at feed stores
con: May contain seeds
|Corn gluten meal||Also marketed as a preemergent weed control for annual grasses in bluegrass lawns.||
pro: High N
con: Inhibits germination
|Fertibor (boron)||White, odorless, powdered substance that is not flammable, combustible, or explosive, and has low acute oral and dermal toxicity.|
|Bat guano||Bat guano (feces) harvested from caves is powdered. It can have either high N or high P depending on how it is processed.||
pro: Stimulates soil microbes
|Blood meal||Blood meal, made from dried slaughterhouse waste, is one of the highest non-synthetic sources of nitrogen.||pro: Available at feed stores
con: Can burn plants if over-applied;
|Bone meal||Bone meal is steam processed and widely available at feed stores and in garden centers. Soil PH above 7 may limit phosphorus plant availability.||pro: High plant-available source of phosphorus
|Fish meal||Fish meal is ground and heat-dried fish byproducts.||
pro: N and P source
con: Heat processed
|Fish bone meal||Made from fish bones that are cooked and ground.||pro: High P|
|Fish emulsion||Emulsions are soluble, liquid fertilizers that have been heat and acid processed from fish byproducts.||
pro: Adds nitrogen and micronutrients
con: Foul smelling
In organic systems, soil fertility, crop nutrient status, and groundcover management are closely linked. As specified under the National Organic Program (NOP), “Organic producers must rely upon animal manures, compost (organic matter of animal and/or plant origin that has been decomposed by microorganisms), and cover crops to supply some, if not all, of the required nutrients for healthy crops.”
Naturally derived soil amendments have variable nutrient levels depending upon the sources from which they were derived. Therefore, nutrient availability from composts and cover crops will be specific for the soil type and crop demand in each orchard. Besides supplying nutrients, soil amendments can increase soil organic matter, balance pH levels, increase microbial activity, improve soil structure and tilth, improve drainage in clayey soils, improve water-holding capacity in sandy or gravelly soils, and help to suppress some root diseases.
The soil can be further improved by through tillage and cultivation practices that maintain or improve the physical, chemical, and biological condition of soil, and minimize erosion.
Under NOP regulations, many commercial fertilizers are permitted, but for most nutrients supplemental fertilizers are allowable ONLY after documenting a deficiency. Both soil and leaf samples can be used for documentation and growers will need to work with their accredited certifying agent to develop an acceptable nutrient program that prevents rather than corrects nutrient deficiencies.
NOP regulation §205.203 specifies that: “Compost must be produced through a process that combines plant and animal materials with an initial C : N ratio of between 25 : 1 and 40 : 1. Producers using an in-vessel or static aerated pile system must maintain the composting materials at a temperature between 131°F and 170°F for at least 3 days. Producers using a windrow system must maintain the composting materials at similar temperature for 15 days, during which time, the materials must be turned a minimum of five times.”
Animal manures may also be used in organic orchards, but they must be incorporated into the soil at least 90 days prior to harvest.
Most commercial compost suppliers will provide a nutrient content analysis report to help calculate application rates for their composts as formulated. Growers should also verify that the compost supplier is following all of the current NOP regulations, and that the accredited certifying agency will approve that compost for organic production.
Preplant cover cropping can improve soil conditions, and provides nutrients and organic matter. Other benefits of cover crops include reducing soil erosion, attracting beneficial insects, and improving site aesthetics, which are especially important in U-Pick orchards.
Nitrogen-fixing legume cover crops are often seeded along with one or more species of annual grass. Nutrient availability will depend upon the growing conditions, species used, seeding rates, and prior soil nutrient status. Typically, the cover crops are mowed/chopped and then incorporated into the soil prior to tree planting. Organic growers can also maintain cover crops or permanent grass covers inbearing orchards to suppress weeds.
Any material, including fertilizers, that is used in a certified organic system must be approved under NOP regulations by your certifier. Many companies now make custom organic fertilizer blends. These products tend to be more expensive than purchasing the materials in bulk and blending them on-site prior to application. There are also numerous companies making liquid nutrients for foliar applications. These can be useful for correcting deficiencies, making maintenance applications for return bloom (e.g., boron and zinc) and improving fruit quality (e.g., calcium).
Applying nutrients to leaves in a spray solution can provide the plant with nutrients such as calcium and zinc that are taken up poorly by the root system, as well as to help correct immediate nutrient deficiencies. Under NOP regulations many of these products are only allowed if there is a documented nutrient deficiency. Growers should contact their certifier to learn how to best document deficiencies, but soil and leaf analyses as well as visual symptoms will likely need to be documented.
Organic sources of foliar nitrogen are derived mostly as a by-product of seafood processing, and come in the form of fish emulsions, fish powders, and fish oils. Rates will depend upon the specific product. Several companies make chelated foliar fertilizer products that are compliant with the NOP. However, there are few replicated trials comparing different organically allowed foliar fertilizer products in orchards. Solubor is a good source of foliar boron, and has proven to be an effective material for increasing leaf boron levels in orchards.
In most Intermountain West soil types, it is recommended that growers apply at least two “spring tonic” sprays that contain boron, zinc, iron and nitrogen in order to stimulate fruit set and flower bud initiation. Also recommended are two to three applications of Epsom salt (for magnesium) at 15 lb/100 gallons of spray, starting at petal fall and continuing for several cover sprays.
Additionally, repeated calcium sprays from the end of shoot growth to harvest have been shown to help improve fruit storage duration. Calcium chloride is typically used as a calcium source, but other formulations may also be acceptable under NOP regulations. The above foliar fertilizer recommendations are based upon trials in non-organic orchards, and it is not known whether recommendations for organic systems would be different.
Numerous microbial-based products are marketed with claims that they stimulate soil biological activity. While these products may be acceptable under NOP regulations, there is little independent scientific confirmation of the manufacturers’ claims.
Well managed organic orchards that include regular organic matter inputs (e.g., cover crops, manures, mulches, composts) typically already have relatively high soil organism biomass and activity, and additional microbial “stimulation” should not be necessary and is unlikely to be cost-effective.