Larger Farm Projects

The Perivoli Rangeland Institute is establishing a number of pilot projects in Namibia to showcase best practices for harvesting encroacher bush and the application of wood and biochar onto the rangeland to encourage moisture retention and the return of perennial grasses, leading to the building of Soil Organic Carbon (SOC).

And in the process justify the earning of offset carbon credits for the farmer.

Bush Harvesting

The larger farm projects start by harvesting encroacher bush through selective thinning and along contour strips by teams of bush harvesters equipped only with manual tools, such as axes and machetes.

Sustainable bush removal is calculated on a Tree Equivalent (TE) or Evapotranspiration Tree Equivalent (ETTE) basis. Based on local research a “rule of thumb” stipulates that the median ETTE/ha and TE/ha that can be supported in a specific rainfall region without adversely affecting the grass layer should not exceed 10 and 1.5 times the mean annual rainfall respectively.

Simply put, on average across the central bush encroached region of Namibia, this translates to roughly 30-50% tree and bush coverage, increasing as the average annual rainfall increases in a north-easterly direction.

The bush species that are cut back are mainly Acacia mellifera, A. reficiens, A erubescens, A. fleckii and Dichrostachys cineria.

The bush harvesting staff are equipped with protective clothing and paid at above market hourly rates.

Bush Filters

The branches of the harvested bushes are laid out on contour lines, known as bush filters.

The branches slow rainwater runoff and provide shade, reducing evaporation. They afford cover from the impact of grazing cattle and game, allowing new seedlings to establish. They also attract termites and microbes that puff up the soil which ponds water upslope, improving infiltration.

Over time, the leaves of the cut bush and those deposited by wind or rainwater runoff reduce soil temperatures before they compost down to release nutrients for uptake by plants.

In addition, some of the branches of the harvested bush are strategically placed in rills, rivulets and gullies to divert or slow the flow of water. In some cases bush is suspended from wires across a rivulet so as to slow the flow of water and divert it onto nearby terrain, improving water retention.



The larger parts of the bush stems are stacked for a few weeks to dry out and then converted to biochar in mobile kilns specially designed by the Perivoli Rangeland Institute for the purpose.

The design of the kilns allows for the burning wood stumps to reach high temperatures (500 degrees centigrade) at which point very little smoke is released, the resulting gases being reburned within the kilns.

Wood is loaded into the kilns in layers to maintain as high a combustion heat as possible, while the bottom layers are deprived of oxygen, thus promoting the anaerobic gasification process known as “pyrolysis”.


Once the stumps have burned down to hot coals, water is pumped up into the kiln from the bottom in a process known as “quenching”.

The quenching causes a steam explosion which cracks and opens the biochar’s carbon crystalline structure expelling the pyrolytic oils.

The contents of the kiln are allowed to sit for roughly half an hour to cool. The liquid is then drained back out of the bottom of the kilns and used as “quench water”, a pest repellent and partial fertiliser that farmers are encouraged to apply after dilution in water to vegetable patches and flower beds around their homesteads.


During the quenching process, the hot coals fragment into a crystalline latticed structure known as “biochar”.

The surface area of one gram of biochar is said to be equivalent in size to the surface area of half a full-sized football pitch.

The kilns are designed to be tipped on an axis, allowing for the biochar to be piled onto the ground for applying to soil.

The kilns can be loaded onto a utility vehicle or trailer and moved relatively easily around the terrain. The aim is to cover as much of the land as possible with biochar.

Soil Organic Carbon (“SOC”)

One of the central aims of the project is to see a return of SOC to the rangeland.

The return of SOC indicates a recovery in the condition of the soil, allowing for a return of perennial grasses whose seeds will have lain dormant in the ground for many years. In cases where perennial grass seeds have been depleted from the soil, reseeding is necessary with seeds collected from areas where perennial grasses suited to the targeted area are abundant.

The improved condition of the rangeland will allow for higher yields from the cattle and game animals that roam the terrain. Farmers are shown, as part of the project, how to protect the land from erosion as a result of over-grazing (the original cause of the erosion to a great extent).

By moving cattle progressively, so as not to over-stress a given location, grazed grasses are given a chance to replenish root reserves during the growing season. Mobile fences and herders are deployed.

The trampling of soil in localised areas by the cattle helps to break down hard crusted soil surfaces and to mix the biochar into the soil. Additionally, the cattle manure feeds nutrients into the soil, transported more easily by the micro-organisms that inhabit soil in the ordinary course down the latticed structure of the biochar.

SOC Measurement

A remote SOC measuring process provided by Downforce Technologies Ltd. (“DTL”) is used to measure the progress in creating SOC.

A DTL Baseline Survey is undertaken before the land clearing starts to show the amount of SOC present at the time and in the preceding six years, ten days at a time, down to a 10 m2 plot resolution. For ground truthing purposes, on the ground soil sampling as well as vegetative assessments are undertaken.

DTL relies on information collected from satellite and other remote imaging techniques combined with datasets of soil classification and type in surrounding areas. The baseline surveys show the maximum theoretical realisable potential SOC that any given area could attain versus the current level. The DTL App, which is made available to the farmer, allows for measurement on a paddock by paddock basis. Follow-up DTL surveys are undertaken annually to monitor and measure progress.

The DTL WebApp takes account of above ground carbon lost during the bush harvesting process so that the net amount of carbon accrued can be measured.

It is intended that in due course the additional carbon sequestered since the start of the pilot projects will be sold into the carbon markets on an annual basis. Depending on the specific site and climatic conditions, these carbon drawdown projects will take upwards of 20-30 years for the full realisable SOC to accrue to a given area.

It is anticipated that it will take a number of years (say three to five) for the additional SOC captured as a result of our specific interventions to become certifiable, at which point sales in the carbon market can commence. It is DTL’s aim that its measurement will count as validation of carbon “additionality”, acceptable to carbon credit buyers.

It is envisaged that most of the carbon credit earnings will be returned to the farmer, other than some set aside to pay for ongoing DTL surveys and future projects on a rolling basis. In addition, some monies will be shared amongst local communities.

It is expected that, in time, no soil sampling will be required once the satellite monitoring algorism has become accurate and widely acceptable. In the case of our pilot projects, soil samples and vegetative assessments are undertaken to validate the findings of DTL.


The Perivoli Climate Trust, which has sponsored the Perivoli Rangeland Institute, pays for the cost of the project and the DTL baseline and follow-up surveys.

The Perivoli Climate Trust is funded by Perivoli Foundation which is a UK Charity dedicated, amongst other things, to addressing land degradation in the countries of Sub-Saharan Africa.

In due course, third party grant funding will be sought to help pay for future pilot projects. We plan to have established at least ten pilot sites (about 500ha total) by the end of 2025, by which point we envisage that carbon credit sales will have started to accrue at the earlier pilot projects, thus proving the concept and approach.

Pilot Projects

Farm Name Location Start Date Hectares under
PRI Restoration Management

Biochar Produced

Baseline SOC
at start of project
(tonnes per hectare)
Max realisable SOC
(tonnes per hectare)
Value of additional SOC
per hectare per annum (USD)*
Krumhuk Windhoek April 2023 75

2023: 10t
2024: 50t

Ombe Hochveld October 2023 250

2023: 100t
2024: 100t

Tsumore Tsumeb February 2024 150? 2024: 200t

*Assumed Carbon price (USD)