A Guide to Making Fertigation Solutions for a Biologically-Intense Container Horticulture

Dr. Richard Freeman

This guide provides instructions for creating fertigation solutions that target any pH level and nutrient demand based on easy to replicate fermentation processes the requires little equipment. The intended audience includes urban horticulturists and farmers seeking to maximize production of sun-grown crops in limited space using sustainable practices. Please see the author’s note at the end of this guide.

Introduction

This guide directly contributes to the knowledge base on conserving and recycling water and nutrients, using local and regional resources – by providing a unique framework for feeding a large horticultural container with biologically derived fertigation solutions. The author has developed this framework over several years of personal observation and loosely-structured research and it has not been established by any scientific community.

Adopting the system will require a cycle of live testing and sampling and periodic data collection to determine precise nutrient needs in the context of the specific plants, HCMs, containers, environments and management styles. The basic necessary steps are explained in this chapter.

This chapter contains five sections. Section 1. describes the reasoning behind the system. Section 2. describes the procedures for preparing the raw materials from which nutrients will be infused into the fertigation solutions, preparing mineral and nutrient supplements from raw materials for the fertigation solutions and preparing the fertigation solutions from the substrates and solutions. Section 3. Procedures for applying the fertigation solutions briefly describes the process and concerns of applying the fertigation solution to plants.

Section 1. Overview of the processes for making biological fertigation solution

Horticultural containers are spatially constrained, nutrient-constrained, lacking robust buffering capabilities and isolated from natural biological nutrient cycling. Thus, a high-performance container cultivation system will require regular intensive nutritional and biological loading to supplement an intensely loaded HCM.

Since using local and regional resources is a priority, this framework uses common resources that should be available on-site or nearby, primarily vegetative matter, but also a significant contribution of animal matter. Transforming these resources into intense nutritional supplements is necessary, and this framework does so using several processes including fermenting, composting, charring, and infusing raw and processed resources into fertigation solutions.

One of the key procedures in this framework involves extracting nutrients from biological matter through the combined use of acid and alkaline solutions and mixing them into a fertigation solution with an optimal pH. The acid and alkaline and acid solutions are also products of fermentation, which chemically denatures biological resources, preparing them for mechanical stirring, aeration and chemical extraction.

The sources of raw biological material vary greatly, including various types of compost, vermicompost and silage. In addition, the formulator can introduce mineral supplements early in the composting cycle, during fermentation or during infusion, stirring and aeration.

The formulator defines the specific nutritional profile of the fertigation solution depending upon plant needs and management style. When initially introducing this system, formulators should establish test plots to determine optimal nutrient levels by correlating chemical properties and nutrient profiles of the fertigation solution to plant growth.

Operators should use pour-through tests to monitor available nutrients in the medium solution, which combines nutrients available from the HCM and from the fertigation solution.

Section 2. Procedures for producing fertigation substrates, supplements and nutrient-rich water solutions

This system for creating fertigation uses a combination of acids and bases to extract nutrients and minerals from biomass and to dissolve mineral salts (for example, burnt bone meal).

2.1. Preparing low-pH solutions

This objective involves fermenting nutrient-rich materials, which partially decomposes the plant materials and denatures a variety of compounds, yielding a nutrient-rich, low-pH solution that the formulator can adjust for various stages in plant development. A by-product is a semi-decomposed, nutrient-rich acidic substrate mash useful as a rich resource for nutrient extraction or for vermicompost substrate. In the fermentation process, the formulator prepares a substrate from raw materials such as manure/straw blends or nutrient-rich plant material, saturates the materials in exudate solution from the same operation, places it in a two-part air-tight container, allows it to ferment for roughly one month, continuously collecting the exudate solution which constitutes the low-pH solution, directs the used substrate to an assigned use and replenishes the substrate supply.

The process involves creating a starter culture and expanding to a reactor that will produce exudate to feed a larger second-stage reactor, which will feed other similar reactors.

2.1.1. Creating the starter culture

Creating the starter culture involves these basic steps:

2.1.1.1. Create a small, air-tight fermentation reactor with two vertically stacked chambers so that the top chamber, which is perforated on the bottom, can hold the solid starter materials as they ferment and the bottom chamber can collect the exudate solution. The example uses two 1-quart plastic food containers. One container is perforated on the bottom, sealed with its matching lid, and stacked within the other to form a reasonably air-tight seal.

2.1.1.2. Create starter material

Create starter material by following these steps:

2.1.1.2.a. Make a carbohydrate-rich substrate with a source of inoculation by environmental microbes. The example substrate mixes one cup of cooked rice with a half cup of chopped fruit (½ -inch pieces) and one cup of sourdough bread for microbe food and inoculation.

2.1.1.2.b. Mix 2 cups of a high-sugar solution with a tablespoon or more of water from a probiotic source. The example uses apple juice mixed with non-fat probiotic yogurt or “water” from yogurt for further inoculation and food for the microbes.

2.1.1.2.c. Mix the liquid materials into the substrate.

2.1.1.2.d. Spread the substrate on a flat surface, allowing exposure to the atmosphere for 4 hours, protected from insects, to inoculate the substrate with spores in the local atmosphere. I use a standard stainless cookie tray with parchment paper.

2.1.1.3. Initiate Fermentation

2.1.1.3.a. Initiate the fermentation by packing the substrate into the top chamber of the reactor and covering it.

2.1.1.3.b. Allow the fermentation reactor to sit in a warm area (64 deg.f) for three days.

2.1.1.3.c. Separate the chambers to determine whether the fermentation is producing exudate solution. If so, determine whether it is fresh or septic. Fresh exudate solution will have a sweet scent and will be yellow or orange, while septic exudate solution will be brown and will smell unpleasant.

2.1.1.3.d. If the bottom chamber is dry, pour another cup of apple juice with yogurt or yogurt water, distributing the solution as evenly as possible.

2.1.1.3.e. When the fermentation reactor is producing enough exudate solution to fill half the reservoir in the bottom chamber, remove the exudate and mix it into a high-sugar solution at a ratio of approximately 1:4.

2.1.1.3.f. Pour it evenly over the surface of the substrate in the top chamber.

2.1.1.3.g. Repeat Step 8 until the fermentation reactor has produced enough exudate solution to fill half or more of the reservoir in the second chamber.

2.1.1.3.h. When the fermentation reactor has produced enough exudate solution to fill half or more of the reservoir in the second chamber, use the exudate solution in the procedure for starting the second stage reactor, as described below.

2.1.1.3.i. Continue adding high-sugar solution at volumes equal to half the reservoir in the second chamber and continue to harvest exudate solution every day.

2.1.2. Creating the second stage reactor

Creating the second stage reactor involves the same steps as creating the starter culture with two significant distinctions:

2.1.2.a. Make 4-1/2 gallons of additional substrate. I use lightly-simmered 1-inch potato chunks in addition to apple chunks (same size). For the reactor I use two stacked 5-gallon plastic buckets with a screw-on lid.

2.1.2.b. Put the substrate into a bucket with perforated bottom and screw-on lid and place that bucket into the other bucket.

2.1.2.c. Pour the mixed sugar-exudate solution from the starter culture evenly over the top chamber of the reactor.

2.1.2.d. Allow the fermentation reactor to sit in a warm area (64 deg.f) for two days.

2.1.2.e. Separate the chambers to determine whether the fermentation is producing exudate solution. If so, determine whether it is fresh or septic. If septic, throw it into the worm bin and start again after thoroughly washing all the buckets and lids. Otherwise, proceed to step 6.

2.1.2.f. Pour the exudate into another bucket and mix it with a gallon of sugar or starch solution.

2.1.2.g. Pour the solution over the surface of the top chamber, distributing it as evenly as possible. If the bottom chamber is dry, add an extra gallon of sugar solution.

2.1.2.h. Repeat Steps 5-7 until the substrate has been saturated and the fermentation reactor has produced roughly 1-1/2 gallons of surplus exudate.

2.1.2.i. When the reactor has produced surplus exudate solution, the exudate solution becomes a resource for the process of assembling the production reactor.

2.1.3. Building the production reactors

The production reactors are similar to the second stage reactors. An operation should divide production among several reactors to spread risk, since pests and pathogens become a larger problem as scale increases. In addition, an operation should factor weight. In the example, a full reactor can weigh 30 pounds or more when full. In general, the number and size of working reactors depends upon the scale of operations and on management objectives. The reference example uses two reactors made from stacked plastic 5-gallon buckets. The top buckets have screw-on lids and are perforated on the bottom.

The substrate should reflect nutritional targets, for example using high-nitrogen and low-nitrogen materials for increasing vegetation and inflorescence, respectively. In the example, the substrate for the vegetative stage is 10 gallons of mixed straw, manure and feathers from a domestic chicken operation, mixed roughly at 6:6:1 by volume. The substrate for inflorescence includes high-carbohydrate, low-N materials such as early fruit and produce (without rot) mixed 3:2 with fresh grain straw. I also use comfrey leaves for a high-nitrogen substrate.

Formulators can also mix mineral supplements into a substrate. For example, I might boost available sulfates, phosphates, potassium and micronutrients by adding bone meal, gypsum, potassium carbonate and ground minerals (for micronutrients).

2.1.4. Inoculating the production reactors

The process of inoculating the production reactors involves building one reactor up to full production with which to inoculate 2-4 others, expanding at the rate that works for the operation. As with the smaller reactors, the exudate solution is mixed into a larger volume of high-sugar solution at an approximate 1:8 ratio. The process includes these steps:

2.1.4.a. Prepare the first production reactor container.

2.1.4.b. Prepare the dry substrate.

2.1.4.c. Prepare the inoculation solution. Mix four cups of exudate solution from the second stage reactor to two gallons of apple juice or other sugar solution.

2.1.4.d. Mix the solution into the substrate.

2.1.4.e. Pack the substrate into the top chamber container.

2.1.4.f. Allow the fermentation reactor to sit in a warm area (64 deg.f) for two days.

2.1.4.g. Separate the chambers to determine whether the fermentation is producing exudate solution. If so, determine whether it is fresh or septic. If septic, throw it into the worm bin and start again after thoroughly washing all the buckets and lids. Otherwise, proceed to step 6.

2.1.4.h. Pour the exudate into another bucket and mix it with a gallon or sugar or starch solution.

2.1.4.i. Pour the solution over the surface of the top chamber, distributing it as evenly as possible. If the bottom chamber is dry, add an extra gallon of sugar solution.

2.1.4.j. Repeat Steps 5-7 until the substrate has been saturated and the fermentation reactor has produced roughly 1-1/2 gallons of surplus exudate.

2.1.4.k. When the fermentation reactor has produced surplus exudate solution to fill half or more of the reservoir in the second chamber, use the exudate solution in the procedure for starting the second and third production reactors.

2.1.4.l. Proceed until all production reactors are producing a surplus of exudate solution according to scheduled needs.

2.2. Preparing high-pH solutions

This objective involves infusing the fermented products from one of two processes, described below. The first process – the silage process – is better suited for the early season. The second process – reactor solids process – is better suited later in the season.

2.2.1. The silage approach

This approach involves fermenting green, nutrient-rich, shredded plant materials, which decomposes plant tissue and denatures a variety of compounds, yielding a nutrient-rich, high-pH substrate similar to a silage. The formulator can aerate and agitate this silage to further separate plant tissue and release beneficial compounds and nutrients, infusing a high-pH nutrient-rich solution for fertigating plants in vegetative growth. Unlike the low-pH fermentation, the formulator minimizes exudate solution and drains the minimal exudate solution immediately to be used elsewhere. The by-product of the entire process is a nutrient meal that can serve as a rich substrate for thermal compost or vermicompost.

2.2.1.1. Producing the silage

In the process, the formulator prepares a substrate from green, nutrient-rich, shredded plant materials such as lawn grass, shredded weeds, herbs and forbs, ferments them in a low-pressure, air-tight container, and infuses them by agitating and aerating them in water solution, yielding a high-pH, green, soupy solution.

Producing the silage merely requires creating a simple 2-part container, obtaining the green plant substrates, packing them and monitoring. One gallon of silage produces roughly 5 gallons of alkaline solution at dilution for application. A reactor maintains quality substrate for three weeks or less, so the formulator staggers production according to use. These steps describe the process in more detail.

2.2.1.1.a. Create a small, air-tight fermentation reactor with two vertically stacked chambers so that the top chamber, which is perforated on the bottom, can hold the solid starter materials as they ferment and the bottom chamber can collect the exudate solution. The example uses three reactors, each requiring two 10-gallon rubber tubs, 12” high x 24” long x 16” long. One container is perforated on the bottom, sealed with its matching lid and stacked within the other to form a reasonably air-tight seal.

2.2.1.1.b. Create substrate for one reactor by shredding lawn grass, forbs and herbs. The example uses ten gallons per reactor, half lawn clippings from a perennial lawn and half coarsely hand-shredded comfrey leaf.

2.2.1.1.c. Pack the substrate into the top chamber of the reactor and attach the lid. The example places a brick on the lid so it can release gas at low pressure but otherwise air intake is minimal.

2.2.1.1.d. Place the reactor in a shady, warm place (64 deg. f).

2.2.1.1.e. After a week, begin checking the reactor every few days for fermentation. When the substrate has visibly changed color and smells sweet, it is ready for an infusion. The average batch takes 10 days.

2.2.1.1.f. When checking for fermentation, check the bottom chamber for exudate solution and remove it.

2.2.1.1.g. Start a new batch periodically according to use. The example uses one gallon or less of silage per day, so starting a new batch every 10 days is adequate.

2.2.2. The reactor solids approach

This approach uses the solids from the upper chamber of the fermentation reactor after it has been significantly decomposed by the active culture. This process usually requires 4-6 weeks, but yields a high-nitrogen, nutrient rich material for infusion.

2.2.3. Infusing the silage or fermentation material

Infusing the silage merely requires mixing it with water at 1:5 and agitating and aerating the water for a short time. The example mixes 5 gallons of water with 1 gallon of substrate in a 8-gallon garden tub and aerates with an air pump, occasionally agitating with a paint stirring wand made for an electric drill with 1/2” shaft. The solution aerates 1-2 hours or according to objectives. The formulator then strains the solution and applies it directly.

Section 3. Formulating green waste compost and vermiculture for nutrient-intensive substrates

The formulator can supplement and adjust the nutritional profiles of green waste compost and vermiculture (hereafter, substrate) by adding nutrient-dense materials and mineral salts to the substrates during their production. With any substrate production, available nutrient profiles in finished substrates will not fully reflect nutrient levels of supplements, because microbes will transform nutrients into organic forms only released when the microbes die and become food for other microbes. By adding charred bone meal and gypsum into the substrates that include brown field grass, horse manure, raspberry cane, biochar and fruit wastes, I produce a vermiculture for blooming. This procedure involves these steps.

3.1. Determining the target nutrient profile

Determining the target nutrient profile based on management objectives, developmental stage, plant type and any other relevant factors is the first step. Expressing the nutrient profile in parts per million will facilitate formulation. Achieving the correct balance of minerals is highly important. For example, the ratios of available nitrogen, phosphorus and sulfur are highly important for plant function. Managing the ratio of minerals to compost mass or volume is less important, since volume can be adjusted to achieve the correct nutrient levels. In general, the nutrient profile should be as dense as possible without affecting substrate production (for example, harming worms).

3.2. Determining the size of the substrate batch

Determining the final substrate production batch size in cubic feet is necessary for determining the weights of application for the nutrient-supplements. Batch size will depend upon intended use, storage space, maximum storage length and other management factors. The example uses one cubic yard, or 27 cubic feet for green waste compost and one-half cubic yard for the vermicompost.

3.3. Determining the nutrient profile of the substrate

Determining the available nutrient profile of the substrate without supplements establishes the reference baseline for formulating the target profile. This step requires sending a sample of the substrate without supplement to a soil laboratory for analysis. The sample should come from a substrate identical to the target substrate, without supplement. The analysis should also account for nutrients that will become available as organic forms are mineralized by microbes. The analysis should report ppm values and should separate nitrates from ammonium.

3.3.1. Formulating the nutritional supplements in parts per million

Formulating the substrate nutritional supplements for any given nutrient involves the arithmetic procedure of subtracting the nutrient level of substrate from the target nutrient level. The resulting end expresses the amount of nutrient required in ppm.

3.3.2. Translating ppm values to weight value

Translating nutritional levels expressed in ppm values into weight per volume values is necessary for applying supplements to substrate production.

3.3.3. Adding supplemental nutrients to the substrate production

Formulators should add supplements to substrate production at specific times appropriate to the supplement with green waste composting, waiting until the end of the thermophilic stage.

3.3.4. Monitoring nutrient levels in finished substrates

Formulators should use lab tests to monitor nutrient levels in finished substrates and to establish estimated averages and standard deviation. Monitoring will require writing a sample design, schedule and budget.

3.3.5. Preparing bone char and gypsum char

Bone char is an excellent source of calcium phosphate without the nitrogen of regular bone meal. Making it is simply involves pyrolizing bones, which involves subjecting them to high heat. Once the bone is adequately charred, it will crumble easily and can be ground. Since bones are constituted by 30% carbon-rich bio-matrix and fat they burn well, though the scent is unpleasant.

Gypsum char requires locating paint-free dry-wall and burning it on a screen to remove the paper while keeping the gypsum separate from the ash.

Section 4. Procedure for preparing the fertigation solutions

The formulator can combine a variety of procedures to achieve the target fertigation solution, which should be applied at full strength. Thus, solution volumes will equal irrigation volumes. Formulators should sample and test solutions initially and periodically to verify that they are meeting targets.

4.1. Combining solutions

Preparing the fertigation solution can simply involve combining alkaline and acid solutions to the appropriate pH and aerating the solution for a short period of time. The example uses 30 minutes to an hour at a pH of 6.5. Formulators can add supplements at the beginning of this procedure.

4.2. Augmenting the high-pH infusion with a low-pH solution

The formulator can also increase nutrient density of the solution by adding low-pH solution to a high-pH infusion. This process will further loosen plant tissue and denature compounds, freeing yet more nutrients from the same substrate. Formulators can add supplements at the beginning of this procedure.

4.3. Adding nutrient-dense substrates as supplements

The formulator can also alter the nutrient profile by adding compost or vermicompost with known chemical properties to the infusion process. However, because of the high salt content of these substrates, they can contribute to a salt-excess in the container leading to salt burn and water-uptake problems. Thus, during vegetative stage, formulators should use the nutrient-dense substrates in moderation. During anthesis (onset), they are highly effective, especially if combined with a low-pH solution as described in these steps:

4.3.1. Determine water dilution volume

Determine water dilution volume necessary for achieving the target pH level in the fertigation solution by following these sub-steps:

4.3.1.a. Add a cup of substrate to eight cups of low-nitrogen exudate solution.

4.3.1.b. Agitate and aerate the solution for one hour.

4.3.1.c. Strain the solution.

4.3.1.d. Test for pH level.

4.3.1.e. Add water in one-cup increments until pH is equal to the target pH.

4.3.1.f. Determine the ratio of water to solution by dividing the cups of water added by 8, the volume in cups of exudate solution.

4.3.2. Make the fertigation solution

This step involves these substeps:

4.3.2.a. Determine the quantity of exudate solution to use, in gallon units, by dividing total application volume (equal to irrigation volume) by the ratio of water to solution.

4.3.2.b. Determine the quantity of water to use by subtracting the quantity of exudate solution from total application volume.

4.3.2.c. Determine quantity of substrate to mix with the exudate solution, by dividing the total application volume by 8.0 or more.

4.3.2.d. Mix half the quantity of water to the determined quantities of substrate and exudate solution and agitate and aerate for two hours.

4.3.2.e. Add the remaining quantity of water, agitate and aerate for a half-hour and strain the solution.

Author’s Note:

This guide is in draft form. It includes no foot notes or references and it contains significant omissions. Anyone interested in republishing using the content in this guide should first contact me, the author, Richard Freeman, to gain permission.

I am interested in co-authoring a final version of this guide.

The information I present is for educational purposes and I am not liable or responsible for anyone’s use or misuse of this information.

I will periodically post updates to this blog by adding a detailed example and providing specific values for chemical and physical properties.