Category Archives: Permaculture gardening techniques

NPK management in Organic farming

N=Nitrogen , P=Phosphorus , K=Potassium (from medieval latin Kalium = Pot of Ashes)

In agro-industrial farming these 3 macro nutrients are obtained by chemical synthesis and mineral extraction. It is now acknowledged that mineral fertilizers impact negatively soil life and provoke its death in fine, making the soil not suitable anymore for plant growth (compact and not adapted to nutrients uptake). External resource : Read this amazing article to understand why

Organic and sustainable management of the soil requires additional understanding, knowledge and some ecosystem monitoring. This mindmap gives a synthesis of NPK nutrients role, the consequences if not available and the different means to provide plants with them in the process of organic farming. (click on the mindmap to enlarge it)



Nitrogen is available from the air in a stable chemical form. Bacteria are the main organisms responsible for the capture (fixation) and the transformation of nitrogen into a plant edible form.

Mycorrhizal fungi play an important role by transporting biologically fixed nitrogen to plants in organic form, for example as amino acids.

The predominant form of Nitrogen found in the soil is protein (in organic matter and organisms).

The next predominant form is inorganic; (NO3, NO2-Nitrite, NH4)

Annuals plants need the Nitrate (NO3) form of nitrogen
Perennials need the Ammonium (NH4) form of nitrogen (feeding trees with nitrate can provoke disease)


Potassium is found in the soil in 4 different forms;

– Potassium as a component of soil minerals
– Fixed potassium
– Exchangeable potassium
– Water soluble potassium

The first 2 forms exist in high quantity in the soil (for example clays of type vermiculite, illite and smectite have a lot of fixed potassium). These 2 forms are not directly edible by plants. Fixed potassium is released in low exchangeable potassium conditions, and mineral potassium is released by weathering, which is a slow process. Recent studies show that silt may represent as well an important reservoir of potassium.

Water soluble potassium which is present in compost is edible by plants but subject to leaching when heavy rains.

Organic matter in the soil favors bacterial, fungal and root activity which accelerate the transformation of non edible potassium into edible one. Macro-organisms (e.g. worms) plays as well an important role by preparing the soil for further bacterial and fungus processing.

To summarize Potassium is an abundant resource which need adequate management (living and active soil ecosystem, good monitoring of compost storage and distribution). Culture rotation may not be needed if the soil ecosystem is very alive and active although guilds will increase biodiversity of the soil ecosystem and concur to its fertility.


Phosphorus is the Achilles’ heel of industrial agriculture and the world food supply (read more at Reserves of phosphate in the world are now handled by a reduced number of countries (Morocco and China) and Phosphate peak could happen in the next decades. Although fossil fuel replacement and water recycling are predominant concerns and see a larger spectrum of solution every day phosphorus world depletion is ignored by most of the population and represents the real challenge when it comes to aggro-toxic farming.

The challenge is simple; plants cannot grow without phosphorus and this mineral become a limited resource. The only solution is therefore reducing, recycling and increase phosphorous availability in the soil. At the moment industrial agriculture is posing a threat to humanity by wasting enormous quantities of phosphorus which end-up in the rivers and the sea.


– A vegetarian diet represent 0.6kg of phosphorus per year, a meat-based diet requires 1.6kg phosphorus a year
– reducing the usage of phosphate fertilizers to the exact required proportions


– Recycling farm waste
– Recycling human wastes (sewage) Since crops leave the farm to feed the population it is necessary to get the phosphorus back to the location of production. The most advanced countries in recycling organic matter or sewage already perform such a recycling.

Increase availability.

Phosphorus concentration varies a lot depending on the soils. As for potassium only a small percentage of it is edible (in solution) by plants. Various techniques allows to increase this availability.

– Increase of microorganisms activity (living and active soil, rich in organic matter). They will mineralize organic matter to make phosphorus available and degrade non edible forms of phosphorus compound to transform them in an edible form.
– Phosphate moves very slowly in soils, deep roots and symbiosis with fungus helps in reaching phosphorus in lower layers of the soil. This can be facilitated by a good soil structure and the mix with perennial plants having in average deeper root system.

To go further and generalize; recycling (mainly avoiding leaching) and soil microbiology are the answers to NPK uptake

Dr Elaine Ingham (microbiology world famous expert) goes further;

– NPK is in enough quantity in the soil for millions of years of agriculture. Just is needed a living soil and its food-web to make it available to plant
– Taking care of NPK fertilizing only is a simplistic vision and more we go more we realize the importance of other chemical elements.
– Classical soil analysis inform only on the ratios of directly available minerals not taking into account the reserve of non directly available minerals that the food web can convert into nutrients. As well soils analysis by giving a PH value does not highlight the fact that PH varies in high proportion at different locations of the plant roots; the plant being able to bio-chemically orchestrate the soil ecosystem (including PH) to feed itself and optimize nutrients exchange at root level.
– Compost, which is an inoculum and not a direct nutrient is key in giving back life to the soil.

Here is Dr Ingham at a conference – a dense and extremely interesting talk

HugelKultur in the tropics

If you have already experienced making a raised bed in the tropics with more or less long periods of drought you may have had a bad experience, seeing your plants drying very quickly because of this kind of earth shaping speeding up the drying process. In this type of gardening only the addition of an irrigation system can maintain a constant and safe level of humidity.

Hugelkultur allows you to asses this issue in the settlement of your raised bed in a quickly drying context. The organic matter acts as a sponge and keep humidity for weeks and months.

On top of that many tropical plants are used to grow in organic matter and it appears that nitrogen deficiency due to a lack of nitrogen compared to carbohydrates is balanced both;

– by intense tropical bacteriologic activity including nitrogen fixing bacteria and

– by fungi participation, developing well in an organic substrate and bringing nitrogen from close-by vegetation.

In our case we will choose to plant Jack beans to accelerate the nitrogen balancing and prepare the bed for future plantation.

How to

The construction of a raised bed using Hugelkultur is fairly simple, in one word : a lasagna of organic matter and dirt.

You may find some diktat on internet about the exact superposition of trunks, branches, mulch, green material, dirt, etc … but nothing is proven with regards to the best choice on this matter.

It sound however logical that the upper layers are made from finer material to give more room for the young roots to grow and the large size material on the bottom to act as a long term decomposition substrate and nutrient/moisture reserve.

Here are some steps, customized for our context;

Hugel Kultur in the Tropics (1)

A clay layer playing 2 roles; protection from the root system of adjacent trees, canalization and retention of the water flow coming from the rain runoff.

Over time the clay layer will crack and allow permeability between the Hugelkultur and the lower layers of the soil to integrate this small ecosystem with the context still reducing adjacent roots invasion.

4 posts will allow to maintain the pile with vertical sides, increasing the surface of the top area

Hugel Kultur in the Tropics (2)

A first layer will act as a sponge for the water runoff and attract worms coming from beneath which will pass the clay layer using the cracks of the drying clay.

Hugel Kultur in the Tropics (3)

Coconut tree trunks are used here for their capability to quickly disaggregate and suck humidity.

Hugel Kultur in the Tropics (4)

Some green material, rich in living organisms are used to fill the spaces and as an inoculum for bacterial activity.

Hugel Kultur in the Tropics (5)

Some mulch

Hugel Kultur in the Tropics (6)

Some soil.

Hugel Kultur in the Tropics (7)

Some smaller however denser timber

Hugel Kultur in the Tropics (8)

Yet another layer of trunks with soil in between.

Hugel Kultur in the Tropics (9)

A green layer (nitrogen and microorganisms) covered with rock dust (minerals)

Hugel Kultur in the Tropics (10)

And again a green layer, as a complement of nitrogen.

Hugel Kultur in the Tropics (11)

And to finish dirt and mulch with the plantation of Jack Bean which have deep roots and will help nitrogen fixation.

Later, other plants will complement the culture, e.g. passion fruit which will climb to the tree close by, corn and squash. Over time the bed will mature and refine itself, being ready for more fragile and sophisticated plants.

The difference with temperate climate hugel-bed is a much higher proportion of organic matter compared to dirt in order to insure moisture retention and adapt to an ecosystem where carbohydrate degradation is fast.

Higher posts could have been used as buttresses to have vertical side walls until the top and help better contain the mulch on the last layer.

Our strategy with regard to HugelKultur in Zone 1 is to create 2 steps projects, here above being the first phase. The second step will consist in creating clay + building rubble walls to have more permanent hearth-shaping containers, easy to maintain by adding organic matter regularly and allowing to create flat top layer for better access and increased plantation area. In Zone 2 and above the Hugelkultur mounts can remain as is and over time will degrade and merge quickly with the garden ecosystem, improving the global texture of the soil.

A water dripping irrigation system will still be put on the  zone 1 raised beds in order to palliate the lack of water. The El Niño episode of 2015 / 2016 is lasting 18 months with 1 or 2 days of rain every 3 months in the south of Bahia where we are located (usually south of Bahia is considered humid tropics). The watering will be reduced since the organic matter acts as a sponge and hold the humidity. In Zone 2 the raised bed will be watered manually only in case of sever drought considering than only cassava and drought resistant plants will be planted there.

Banana Circle

Banana trees like;
– Water
– Sun (for growth and light shade for fructification)
– Organic matter
– Light soil with good drainage

Banana trees dislike;
– Wind and associated drought
– Compact and heavy soil

The Banana circle, which is a round cluster of Banana trees is the best answer to these requirements;
– The center of the circle collect and mechanically store organic matter and humidity. The roots of the banana trees will develop mainly there to catch humidity and organic nutrients
– The cluster of trees act as a mutual wind protection
– The mount of the volcano border where are planted the banana trees is made of soft soil facilitating root development.


Banana will not grow on a soil compacted with clay. Roots will have problems to develop and water logging will provoke the stem to rot. In this type of situation a large hole is made to remove the clay and amend it with silt or sand as shown in the picture.

A rule; there is never enough mulch to feed a banana tree unless you use the banana tree to recycle used water. Even in the latter case the banana tree will prefer brown water recycling (rich in fibers) than for example sink water recycling. So; be generous with organic material and always keep the banana stems you cut (when collecting the bananas) back into the center of the circle.

Banana circles love waste water from human. It is a reason why Banana is a plant of choice in tropical Permaculture. For every spot where human use water (shower, sink, bio-digestor populated by water closets, urine disposal from dry toilets …) a Banana Circle can be setup to capture and reuse the polluted water. It is even advised not to gather all polluted water in one central place but spread the water usage recycling to various banana circles so to multiply this resource usage and make sure you capture all nutrients you can from human wastes.

By setting up Banana Circles for water recycling you create a oasis of humidity and a fertility island. From there you may start guilds and/or stretch the island to extend it.

Various strategy can be setup in case of recycling…

Corridor and vegetation stretching using Banana Circles

A corridor of vegetation between 2 banana circles can be created to speed up the vegetation (when in a rehabilitation focus) stretching process. In this case the terrain and the sectors analysis and existing vegetation situation may help to define the most protected and humid direction (wind, sun, rain) to ease the propagation and to localize the banana circles.

Waste water volume recycling

The tubulation populating a Banana Circle can be diverted or multiplied over time depending on the quantity of nutrients contained in the waste water, to create for example a second banana circle more down the hill and split the flow in two.

Spreading of recycled chemical elements

Exchanging the cut stem from one banana circle to another can be done depending on the type of human waste. For example if a banana circle receives water from a spot dedicated to washing clothes (washing machine or sink) you may expect a high level of phosphorus (sodium triphosphate compound) and other additives that, if considered as a pollution when in excess may become a resource if degraded and recycled in your garden.

Most of detergents have for example a pH>9.5 which can be useful if your land is very acidic. In this case you may add a certain quantity of sand and spongy mulch inside the banana circle hole and transfer it somewhere else after a while. The design of the banana circle should be adapted to this regular transfer and some soil analysis made time to time to analyze the speed of acidity change.

If you made a biodigestor by evapo-transpiration using building remains (cement blocks, concrete powder, …) you may expect your banana stems to have a high concentration of calcium and silica, etc…

Permaculture not only allow to get rid of pollution but help here to transform the waste in many useful resources; minerals and water.

Banana Circle and Swale for water run-off recycling

Since banana circle love water a good location is to position one down the hill of a swale on the top of the water lens. This strategy implies a two steps method; first build the swale then after a while use the sediments and sand accumulated in the swale by erosion from water run-off to create the soft ground for banana circle construction. If you use directly the soil down the hill you may assume that erosion has kept only hard soil not suitable for banana roots.

Banana Circle Shower

Organic degradation is quicker with the presence of a shower and requires regular addition. The good news is that the degradation will benefit the banana trees intensively.

The picture below shows the evolution of a banana circle shower before (just after having planted the banana trees) and after (after few months). The design has now evolved with a dome in the center.


Harvesting bananas

Each stem will give a cluster of bananas. Picking up banana one by one as they get ripe allow to avoid the full cluster to ripe at the same type. This happens when removing the cluster of banana at once. However letting the banana ripe on the tree will mean birds taking their share. Once removed all bananas the stem is cut in pieces (e.g. 50 cm long) and put back into the center of the banana circle as organic matter. You may as well remove the wilted leaves regularly if you have time and not too many of banana trees and dispose them in the center of the circle as well.

Some photos of Banana Circle showing the evolution of the plants;


Banana Circle – Before, on a future outdoor shower


Banana Circle – After, on the outdoor shower


Before, getting the gray water from a sink


After, getting the gray water from the sink. The banana circle provides, once adult, shade when cleaning the dishes.


Before. it will get the urine diverted from the dry toilets


After few months, photo taken from the cabin of the dry toilets. Urine contain a lot of nitrogen. In this case it will be important to return the trunks and leaves (after banana harvesting) to the center of the banana cluster since banana trees may have a lack of carbohydrates compared to nitrogen and water.

African Keyhole Garden

The African keyhole garden is different from the Mandala design since the center of the raised bed is dedicated to nutrients and the access to the plants is done from the outside.


This example of a structure is made with bricks having no stones in Bahia Atlantic border.
Note the disposition of the bricks to increase the wall cohesion.
The V shape inclusion is the access path to the future basket of nutrients.


Here we use hardwood to create the basket frame.


The frame is hold together using wild vine harvested in the forest.


We add cardboard on the periphery to reduce weed invasion.


The next step is the construction of the raised bed. You may find many recipes on internet about the different layers; every one has his own method; …compost, mulch, brown and green manure, ashes, biochar, etc… The last layer is made of mulch, for example the leaves of a leguminous tree to provide with nitrogen and protect from the sun.


Compost, mulch or manure is added in the basket. The basket is regularly fed by organic matter (mulch, kitchen scraps, animal manure, …). The idea is that watering the basket will bring the organic nutrients to the raised bed over time. The basket design acts as a nutrient chamber easy to fill where composting is accelerated and humidity better kept as well.


You may plant a guild of Papaya, dwarf banana and Pigeon Pee.

The African Keyhole is well adapted to hot and dry places