Soil restoration and use: andosols and regolith

Soil restoration and use: andosols and regolith

As part of the long-term DREVO program for land restoration, creation of forests, forest-steppes and sustainable forest gardens

1. General concept

The long-term DREVO program must address not only the already formed soils, but also the deeper mineral base of the area.

The project examines two fundamentally different natural resources:

andosols— soils formed mainly from volcanic ash and other volcanic materials;

regolith— loose or disintegrated material located above the bedrock and including weathered rock, saprolite, mineral fragments, sediments, and sometimes formed soil horizons.

Regolith should not automatically be considered fertile soil. It can be:

almost sterile mineral substrate;

highly weathered material;

sand or gravel covering;

volcanic ash;

loess;

alluvial or slope deposits;

salted material;

contaminated industrial substrate;

the basis for the gradual formation of new soil.

In a geological sense, regolith is a covering of loose and weathered material over more solid bedrock. Its composition and depth can vary significantly even within a single area.usgs.gov)

The main objective of the project:

not just use mineral material as soil, but gradually transform it into a stable living soil system.

Recovery sequence:

parent rock or regolith → mineral substrate → primary biofilm → vegetation cover → organomineral horizon → young soil → forest soil → stable soil of forest garden.

2. Andosols

2.1. What are Andosols?

Andosols form predominantly in volcanic materials rich in volcanic glass. They are particularly common in areas of modern and ancient volcanic activity.isric.org)

They are often characterized by:

high porosity;

relatively low bulk density;

good moisture capacity;

developed aggregate structure;

the ability to accumulate significant amounts of organic matter;

high biological productivity with favorable management;

special mineralogy associated with allophane, imogolite, ferrihydrite and active compounds of aluminum and iron;

strong phosphorus binding.

Many Andosols have high agricultural potential, but their productivity is often limited by intensive phosphate fixation. This property is corrected by using organic matter, liming, silicon-containing materials, and carefully calculated phosphorus nutrition.FAOHome)

2.2 Why are Andosols valuable for the project?

With its structure preserved, Andosol can become one of the best bases for:

mountain forests;

wet forest gardens;

fruit and nut systems;

nurseries;

berry bushes;

coffee, tea and other perennial crops in a suitable climate;

accumulation of organic carbon;

water-regulating plantings;

slope restoration.

Its physical properties can ensure good root and water penetration. However, the properties of a specific site must be confirmed by analysis, as Andosols vary significantly in acidity, depth, leaching rate, volcanic material composition, and organic content.

2.3. Main risks

Andosolis cannot be considered automatically invulnerable.

Their degradation is possible due to:

deforestation;

fires;

deep plowing;

overgrazing;

overdrying;

compaction equipment;

slope exposures;

water and wind erosion;

loss of organic horizon;

uncontrolled application of fertilizers;

contamination by heavy metals and industrial dust.

In an undisturbed state, volcanic soils can resist erosion well, but after a fire or severe disturbance, their hydrological properties can deteriorate sharply.iforest.sisef.org)

Removing the dark, upper organomineral layer is particularly dangerous. Its formation may have taken decades or centuries, and its rapid restoration is impossible.

3. Principles of Andosols Recovery

3.1. Saving an existing profile

The first principle is to preserve the established horizons as much as possible.

It is necessary to avoid:

removal of the fertile soil layer without necessity;

mixing of the surface horizon with poor lower material;

movement of heavy equipment on wet soil;

long-term storage of removed andosol in high heaps;

leaving the soil uncovered;

removal of organic matter from the site without compensation.

When constructing or creating water structures, the removed top layer must:

stored separately;

protect against erosion and drying out;

preserve seed and microbial material;

return to the surface of the restored area.

3.2. Restoration of the organic horizon

Used:

leaf litter;

wood chips;

compost;

safe biochar;

chopped branches;

cover crops;

legumes;

perennial cereals;

forest litter from local, safe sources;

green mass that does not contain pollutants.

Organic matter is added gradually. Avoid turning the area into a thick, anaerobic layer of undecomposed material.

3.3 Surface protection

In the early stages the following are used:

hydroseeding of native grasses;

mulch;

anti-erosion mats;

branches laid out along the contour;

living shrub barriers;

terracing;

contour stripes;

small water-retaining shafts.

Soil structure directly influences water movement, aeration, root development and erosion resistance. (FAOHome)

3.4 Phosphorus Management

Since Andosols are very strong phosphorus binders, simply increasing the fertilizer dose is not always the best solution.

Required:

laboratory determination of available phosphorus;

pH analysis;

assessment of active aluminum and iron;

use of organic materials;

local rather than continuous application;

use of mycorrhizal plants;

selection of species capable of effectively using poorly soluble forms of phosphorus;

elimination of excess phosphates near water bodies.

The goal is not to apply maximum phosphorus, but to create a stable biological cycle.

3.5. Working with acidity

Some of the andosols have an acidic reaction.

Depending on the results of the analysis, the following may be applied:

limestone;

dolomite;

wood ash only from pure controlled raw materials;

basalt flour;

organic materials;

plant species adapted to moderately acidic soil.

Liming is carried out gradually, since a sudden change in pH can disrupt the microbial community and alter the mobility of metals.

4. Using Andosols in the project structure

4.1. Protected areas

On the deepest, wettest and best-preserved Andosols, priority is given to:

natural forest;

old-age kernels;

seed groves;

watershed forests;

areas of natural renewal.

High quality andosol should not be completely converted to intensive agriculture.

4.2. Nature-forming forest

Depending on the climate zone, the following can be used:

oak;

linden;

maple;

ash tree;

beech;

chestnut;

walnut;

elm;

fir;

cedar pine;

native volcanic forest species.

The choice is determined not by the overall attractiveness of the tree, but by:

altitude above sea level;

temperature;

amount of precipitation;

acidity;

wind load;

soil depth;

fire risk;

local ecology.

4.3. Sustainable forest garden

On safe andosols it is possible to create productive zones:

fruit trees;

nut-bearing;

berry bushes;

grapes;

perennial vegetables;

medicinal plants;

mushroom cultures.

At the same time, part of the natural tree framework is preserved, and fruit crops are gradually integrated into it.

4.4. Nurseries

Due to their good moisture holding capacity and structure, individual Andosols can be particularly valuable for nurseries. However, it is necessary to monitor:

overwatering;

acidity;

phosphorus availability;

damage to the structure due to frequent processing;

transfer of soil-borne pathogens;

removal of fertile material along with seedlings.

5. Regolith

5.1 What is meant by regolith?

In the DREVO project, the term "regolith" is used to describe the loose mineral cover above the bedrock, which does not necessarily yet have full soil properties.

Regolith may include:

weathered rock;

saprolite;

crushed stone;

gravel;

sand;

dust;

volcanic ash;

loess;

sediments;

detrital slope materials;

mineral waste from quarries;

man-made displaced rock.

Weathering breaks down solid rock and forms fragmented or granular material that can later support terrestrial life and contribute to soil formation. (pubs.usgs.gov)

5.2. Regolith as a resource, not ready-made soil

Regolith may contain useful mineral reserves, but often has serious limitations:

almost complete absence of organic matter;

low biological activity;

weak aggregate structure;

deficiency of available nitrogen;

limited phosphorus;

unstable water regime;

high rockiness;

excessive water permeability or, conversely, compaction;

toxic minerals;

increased concentration of metals;

acidity or alkalinity;

tendency to erosion.

Therefore, the aim of the project is to carry outpedogenesis, that is, controlled formation of soil based on regolith.

6. Regolith classification for the project

Before use, regolith is divided into functional categories.

Category RG-1 - Biologically promising

Material:

not contaminated;

has a suitable mineral composition;

retains some moisture;

accessible to roots;

does not contain dangerous excess salts;

can quickly transform into soil.

Application:

forest-steppe;

reforestation;

protective strips;

future forest garden.

Category RG-2 - poor but safe

Features:

low in nutrients;

almost no organic matter;

poor water holding capacity;

high rockiness.

Application is possible after:

creation of a watershed;

introduction of organic matter;

plantings of pioneer species;

erosion protection.

Category RG-3 - physically challenging

Material:

compacted;

excessively clayey;

almost impenetrable;

too loose;

unstable on a slope;

contains large fragments.

Requires engineering soil preparation.

Category RG-4 - Chemically problematic

Possible:

high acidity;

alkalinity;

salinization;

excess boron;

toxic aluminum content;

sulfide minerals;

heavy metals.

Use is permitted only after analysis and special remediation.

Category RG-5 - hazardous or unsuitable

This includes materials containing:

hazardous industrial waste;

asbestos;

radioactive components;

high concentrations of lead, cadmium, arsenic, mercury;

acid-generating mine rocks;

other uncontrolled pollutants.

This material is not used in food, forest or public areas without insulation and a separate engineering project.

7. Formation of soil from regolith

Stage 1. Geological and chemical survey

The following are determined:

origin of the material;

depth;

granulometric composition;

mineralogy;

pH;

electrical conductivity;

carbonate;

year;

available macro- and microelements;

heavy metals;

ability to form acid runoff;

water permeability;

slope stability.

Stage 2. Formation of relief

Regolith cannot simply be leveled evenly.

Created:

stable slopes;

terraces;

micro-drops;

water collection bowls;

contour shafts;

stone lines;

safe overflows;

areas of fine soil accumulation;

Protected landing pockets.

Stage 3. Creation of fine soil

For very large and rocky material, the following are used:

mechanical crushing of a part of the rock;

mixing of fractions;

adding safe clay;

introduction of fine mineral material;

local arrangement of landing pockets;

retention of natural dust and sediment.

It is not necessary to completely crush the regolith. Large fragments:

protect the surface;

reduce evaporation;

create a microclimate;

retain small particles;

provide habitats.

Step 4. Adding organic matter

At the initial stage, organic matter is introduced mainly locally:

into the runways;

in pockets;

around bushes;

along watersheds;

under mulch.

Used:

compost;

wood chips;

straw;

leaf litter;

green mass;

safe biochar;

fermented organic material.

Large doses of fresh organic matter should not be buried deep into poor regolith, as this can cause anaerobic processes.

Stage 5. Biological colonization

The following are entered sequentially:

bacteria and biological films;

lichens and mosses - where they naturally develop;

annual herbs;

perennial cereals;

legumes;

shrubs;

pioneer trees;

long-lived nature-forming trees;

forest undergrowth;

productive elements of the forest garden.

Stage 6. Formation of the organomineral horizon

Through litterfall, root death, microbial activity and mineral weathering, a new surface horizon is formed.

Key indicators:

the emergence of stable aggregates;

increase in carbon content;

decrease in density;

improved infiltration;

increase in moisture capacity;

development of the mushroom network;

increase in the number of soil animals;

the beginning of natural plant regeneration.

8. Pioneer plants for the regolith

There is no universal set. Species are selected based on the climate and substrate chemistry.

For dry and rocky areas

local drought-resistant cereals;

fescue;

wheatgrass;

sainfoin;

alfalfa at the right pH;

to look at;

sucker;

juniper;

pine;

oaks of dry habitats;

local thorny bushes.

For wet areas

willow;

alder;

poplar;

sedges;

sieves;

reed communities;

moisture-loving herbs.

For acidic substrates

birch;

pine;

some species of alder;

Heather;

acid-loving cereals;

local forest species.

To stabilize slopes

perennial cereals;

shrubs with branched roots;

willow on wet slopes;

juniper;

local groundcover plants;

trees adapted to shallow soil.

Pioneer species are used as a temporary protective system. They should not automatically become the sole composition of the future forest.

9. Transition from regolith to forest

0–5 years

analysis;

relief formation;

erosion protection;

water management;

local application of organic matter;

primary vegetation cover.

5–16 years old

perennial herbs;

shrubs;

pioneer trees;

the first long-lived trees;

accumulation of litter;

monitoring of soil formation.

At 16 years of age, the site undergoes its first extensive environmental assessment and can receive a preliminary or permanent natural zone passport in accordance with the DREVO system.

16–35 years old

expansion of tree groups;

creation of a forest-steppe mosaic;

strengthening the mushroom network;

formation of a young humus horizon;

planting oak, linden, maple, ash, cedar pine and other frame species.

35–75 years old

formation of young forest;

development of several tiers;

the appearance of natural undergrowth;

creation of light windows;

beginning of the careful inclusion of fruit and nut crops.

75–150 years

mature forest soil;

uneven-aged wood composition;

nature-forming framework;

forest-steppe and aquatic zones;

sustainable forest garden on the safest and most fertile sites.

150–300 years

natural renewal;

replacement of the first generations of trees;

preservation of old-age kernels;

development of a deep soil profile;

adaptation of forest composition to changing climate;

transfer of passported zones to future generations.

10. Artificial soil compositions

In some cases, regolith can be used to create the designed soil.

Possible structure:

Lower mineral layer

large regolith;

drainage material;

stable weathered rock.

Middle root zone

fine regolith;

sand;

loam;

clay;

mineral supplements;

a small proportion of stable organic matter.

Upper biological layer

mature compost;

local safe soil;

leaf humus;

mulch;

roots of ground cover plants.

Precise proportions cannot be set universally. They are calculated based on:

textures;

moisture capacity;

climate;

appointment;

mineral composition;

profile depth;

plant requirements.

11. Use of volcanic regolith

Fresh volcanic material may be a promising source of minerals, but it is not ready-made fertile soil.

To master it you need:

surface stabilization;

reduction of wind transport of ash;

water management;

accumulation of organic matter;

colonization by microorganisms;

introduction of nitrogen-fixing plants;

control of phosphorus availability;

acidity assessment;

testing for toxic elements.

Over time, volcanic regolith can transition to young volcanic soil, and then, under suitable conditions, to soil with Andean properties.

12. Use of regolith in the project's economy

Once safety is confirmed, regolith can be used for:

formation of terraces;

anti-erosion shafts;

restoration of quarries;

creation of forest landing sites;

construction of permeable roads;

mineral filter devices;

creation of substrates for non-food plants;

obtaining mineral fractions;

formation of artificial soils;

devices for nursery mixtures;

slope restoration.

But before moving the material, it is necessary to evaluate:

is the contamination transferred?

is the natural profile not destroyed;

is acid runoff being created;

does the water regime change?

whether valuable geological or soil resources are being removed.

13. Restrictions

The project prohibits:

to extract andosol as ordinary commercial soil without environmental justification;

remove the top layer from natural volcanic forests;

mix contaminated regolith with clean soil for "dilution";

use unknown mine material in forest gardens;

planting food plants on untested substrate;

bury large volumes of fresh organic matter deeply;

carry out continuous planting of trees without assessing the water balance;

consider the appearance of vegetation as evidence of soil safety;

remove mineral material from protected natural areas;

create monocultures on restored regolith.

14. Andosol and regolith passport

A special soil-geological section is added to the digital passport of the natural zone.

For andosoli are fixed

origin of volcanic material;

soil classification;

profile depth;

organic carbon content;

bulk density;

moisture capacity;

pH;

available and bound phosphorus;

active aluminum and iron;

state of the structure;

degree of erosion;

history of fires;

vegetation type;

mode of use.

For regolith are fixed

geological origin;

depth to bedrock;

degree of weathering;

granulometric composition;

mineralogy;

stoniness;

pH and salts;

metal content;

water permeability;

slope stability;

depth of forming soil;

organic matter content;

stage of biological development.

Development statuses

15. The main principle of the project

Andosol must be preserved and restored first and foremost. The regolith must be studied, stabilized, and gradually transformed into living soil.

Basic sequence:

Geological diagnostics → Safety assessment → Terrain and water management → Surface protection → Organic matter addition → Biological repopulation → Grasses and shrubs → Pioneer forest → Nature-forming trees → Mature forest soil → Sustainable forest garden.

On a scale of 150–300 years, regolith is viewed not as a barren material, but as the foundation of future soil, and andosol is viewed not only as an agricultural resource, but also as a valuable living natural heritage.

It is logical to link this section with the system of ecological certification: the passport of a plant and a natural zone includes not only the soil type, but alsothe stage of transformation of regolith into a living soil profile.

A forest garden should not be described as “trees + bushes + herbs”, but as a system of water, soil, light, roots, pollinators, crops and gradual change of vegetation.

When properly designed, agroforestry systems can simultaneously improve soil fertility, water retention, wind protection, biodiversity, and production sustainability. However, with improper density and species selection, trees begin to compete with crops for light, water, and nutrients.FAOHome)