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Self-renewing Fertility in Edible Forest Gardens: Part 1
Part 1 of a 2-part series
The forest-gardening approach to fertility emphasizes strategies employed in the design phase that should reduce the need for work and expensive inputs later on down the line. Many basic characteristics of forest gardens support self-renewing fertility by their very nature: perennial plant roots provide consistent root-zone resources to the soil food web; lack of tilling allows undisturbed development of the soil organism community; consistent mulch provides stable food resources for the decomposers and a stable soil environment for everyone who lives down there; and so on.
While all of the following strategies are important for creating self-renewing fertility, this section provides in-depth information on nitrogen-fixing and dynamic accumulator plants.
Use Site Analysis and Assessment and Niche Analysis
To create self-renewing fertility, you must begin with a careful assessment of your soils. Make sure to assess nutrient levels in both your topsoil and your parent materials so you can determine long term fertility prospects and needs. Also, evaluate the soil profile so you can identify possible problems of compaction, high water tables, and other factors that may influence the plants' belowground resources. Desired species niche analysis tells you which soil conditions your plants prefer; The site and niche analyses will guide you in developing a garden design and a site preparation plan that will in turn determine how to use the strategies listed below.
Maximize Root Penetration of the Soil Profile
Making sure that plants can get their roots deep into the soil profile gives them the greatest access to the most soil resources. It allows plants to absorb nutrients· leaching into the deep soil and those released by weathering of the parent materials. This aids nutrient recycling and conservation and ultimately enriches and deepens the topsoil as the plants drop leaves on the surface and their roots die throughout the soil profile.
Create Healthy Soil Food Webs
With proper care, subterranean micro herds and fungal allies offer tremendous nutritional benefits to our plants. To receive these benefits we must treat them well by minimizing compaction, adding organic matter, and minimizing tillage and other forms of soil disturbance. Perennial plants help sustain a year-round root-zone soil food web capable of storing more nutrients than can the decomposer food web by itself Mycorrhizas are especially important and beneficial for plants and for nutrient storage and transport.
Fertilize the Way Nature Does: From the Top Down
By mimicking natural fertilizing processes we enable the ecosystem to develop nutrient processing pathways that will run properly even when we aren't around to do the work. This means using nutrients in the form of organic matter and rock powders whenever possible, and applying them appropriately. Though it may be slower, feeding the soil from the surface with organic materials creates the biological infrastructure the ecosystem needs to function properly. Placing organic matter or compost deep in the soil profile, however (say, in the bottom of a planting hole), can make matters worse: less oxygen is available deeper down, so the organic matter often decomposes anaerobically. This in turn can kill roots and beneficial soil organisms. Mulching and fertilizing the soil surface allows leaching, plant roots, and decomposers to act naturally, reduces disturbance to the soil profile, and works in harmony with natural soil-building processes.
Apply Mulch, Compost, and Amendments Appropriately
Mulch is one of the most critical components of forest gardens. A mimic of the litter layer found on forest floors, mulch has numerous benefits. It is not without its drawbacks-notably the cozy habitat it provides slugs and voles-and one must apply it to an appropriate depth.
Compost provides organic matter and nutrients and also inoculates the soil with beneficial organisms. However, compost is usually expensive. It is best mixed into the soil during site preparation: or used as a top dressing after planting, if the soil needs much help. Never fill tree-planting holes with compost, as it can lead to "pot-bound" roots and anaerobic soil conditions. Always mimic natural soil profile structures by spreading compost on the soil surface, or at most mixing it into the topsoil, then covering it with mulch.
Some perennial gardeners pull back their mulch, add 1 to 2 inches (2.5 to 5 cm) of compost to their gardens, and then remulch-every year. This certainly creates a healthy garden, but it is not self-maintaining, self-renewing fertility by a long shot. If the soil is in rough shape, yearly additions of compost might make sense until the plants get well established and serious nutrient cycling and conservation get going in the ecosystem. Otherwise, an early boost, followed by mulch, should be enough. It can take five to seven years, or more, for forest gardens to firmly establish their own nutrient cycles. However, with good design using fertility-building plants, the garden will get there eventually, making its own compost every year with no effort on your part.
For greater amounts of nutrients, and to make up for serious nutrient deficiencies, you can use a wide variety of organic soil amendments. Again, we should most often use these as an early system establishment boost until the garden cycles get going. In areas with some combination of high rainfall, warm winters, nutrient-poor parent materials, and degraded top soils, you may need to add amendments every few years to account for leaching losses, even after the nutrient cycling and conservation system gets going.
Create Lush Vegetation and Abundant Organic Matter
Plants and organic matter play key roles in the anatomy of self-renewing fertility, co creating a dynamic, nutrient-conserving system. More vegetation means more water transpired from the soil, which reduces nutrient leaching. It also means more nutrients built into biomass, which then becomes organic matter. More organic matter means more cation exchange sites and, thus, more room in the soil to store nutrients.
Emphasize Aggrading, Midsuccession Habitats
The aggradation phase of succession is when ecosystems exhibit the greatest control over nutrient flows. The aggradation phase is also when the ecosystem most rapidly converts the greatest amounts of nutrients and sunlight into biomass and builds other forms of natural capital. Emphasizing the aggradation phase will therefore maximize nutrient conservation, storage, and recycling. This means creating midsuccession habitats ranging from old field mosaics to sun loving pioneer-tree woodlands. Since most of our best crop trees and shrubs are competitor-strategist plants adapted to such environments, we are in luck. We just need to build the complete ecosystem with diverse components to make it work.
This is Part 1 of a 2-Part series that was excerpted with the kind permission of the publisher and authors from:
Jacke, Dave, with Eric Toensmeier. 2005. Edible Forest Gardens, Vol. 2, Ecological Design and Practice for Temperate Climate Permaculture. Chelsea Green Publishing, White River Jct., Vermont. 654 pp.
Eric Toensmeier has studied and practiced permaculture since 1990. He has spent much of his adult life exploring edible and useful plants of the world and their use in perennial agroecosystems. He is the author of Perennial Vegetables and co-author of Edible Forest Gardens with Dave Jacke. Both books have received multiple awards. Eric manages an urban farm project for Nuestras Raices Inc., which provides immigrants and refugees with access to plots and start-up support on a 30-acre farm. He gives courses and presentations in English, Spanish, and Botanical Latin.