At the center of the production aera, a space dedicated to growing vegetables and herbs will be arranged to form two Mandala gardens in order to maximize the use of the space. Making a vegetable garden on forest soil and having a good production of herbaceous plants requires some soil modifications. Indeed, the woody litter (rich in tannins and terpenes poor in nitrogen) of the forest will be preferentially, if not exclusively, broken down by fungi because: (i) Fungi do not need as much nitrogen (N) as bacteria to grow (fungi have a C/N ratio of 10 to 20 while bacteria have a C/N ratio of 5 to 10). (ii) Fungi secrete enzymes able of cutting long complex molecules of tannins, lignins and terpenes.
Fungi secrete acids that are unfavourable to the development of bacteria, so the forest soil is rather acidic and populated mainly by fungi. In acidic soils, nitrogen will be in the form of ammonium (NH4+). NH4+ is an easy nitrogen (N) source for plants because it can directly be used for the synthesis of amino acids, which make up the proteins. However, NH4+ is not available in abundance because it remains bound to negative soil particles and, in addition, storing NH4+ is quite toxic to cells. Studies have highlighted that NH4+ is used preferentialy in the production of seeds and fruit as well as in plants with slower growth. The growth of fast-growing annuals and short cycle requires that organic matter be decomposed rapidly to accelerate nutrient recycling. On the other hand, the mineralization of nutrients (including N) must be rapid in order to allow plants to grow quickly and concentrate a lot of nitrogen in their biomass. It is the bacteria that perform this rapid decomposition and mineralization of organic matter, a soil growing vegetables has a low fungal-to-bacteria ratio (F:B ratio). Also, bacteria secrete gelling proteins that stick to each other and to soil particles in order to be more resistant to the phenomenon of rinsing in case of rain. These proteins are basic and therefore, helps to increase the pH of a soil dominated by bacteria, bringing the nitrogen to be in the form NO3-. NO3- is the prefer source of nitrogen for fast grawing plants.
So we’re going to try to reverse the microbial population of the soil on which we want to produce vegetables so that it has even amount of fungi and bacteria. Two techniques will allow us to do this: (i) Amend the soil with basic elements, lime (CaO which, when mixed with water, has a pH of 11-12); (ii) Promote nitrogen-rich herbaceous bedding rather than tree bedding because it contains tannins and terpenes that cannot be decomposed by bacteria
(i) Adding lime to the soil will also initiate the assembly of clay-humic complexes that are so important for soil fertility. In fact, the clay-humic complexes stabilize the soil, prevent erosion and increase the cation retention capacity of the soils. The clay molecules, which have many negative charges on their surface, repeal each other, so they become suspended as soon as it rains and will thus flown away. The same applies to organic matter molecules (O.M) which are also negatively charged. The calcium (Ca2+) of lime has two positive charges, it will bind the negative charges of clay molecules and organic matter in order to create clay-clay complexes, M.O-M.O and clay-M.O. Following their fixation with the Ca, Clay and M.O molecule complexes are less negatively charged and heavier so they repeal less and they are less easily suspended; hence, soil erosion slows down. Complexes are also less accessible to weathering agents, making soil compounds more stable. The soil cations (K+, Ca2+, NH4+, Mg2+, etc.) essential nutrients to the plant, will bind to the complexes, still negatively charged, and be retained in the soil, even in case of heavy rain.
The majority of recyclers release the nitrogen they have in ammonia form. Therefore, it is necessary that NH4+ be converted into NO3- in order to allow fast-growing plants to have a sufficient nitrogen resource. This is achieved through a two-step process (performed by bacteria of 2 different genera living in symbiosis) called nitrification. The addition of lime will increase the soil pH and allow the development of these bacteria.
(ii) Using a grassy cover (nitrogen-rich; C/N= 10-40) rather than woody (nitrogen-poor; C/N= 50-100) promotes the development of bacteria that rapidly decompose and mineralize organic matter because, in the presence of sufficient food resources, they multiply much more rapidly than fungi. Decomposition and mineralization, being carried out mainly by bacteria, will be very fast and therefore nutrient availability in the soil will be important for rfast growing plants.
In a Mandala garden, where the crop beds are accessible from one, or more, path(s) in the form of a lock, the entire growing space is connected in such a way as to allow plants to benefit from the relationships established with its many neighbours.
The two Mandala gardens will be arranged in order to form the sign of infinity, which corresponds to the abundance that we believe we can obtain in La Evidencia if we stick to the pattern of Nature. So the teachings of Nature are:
1. Mixed planting: Nowadays, scientists are beginning to understand why the places left wild are very diverse in plant species; the most important benefits are the differences and complementarities between the species in terms of:
- Symbiosis with mycorrhizae. [If you want to know more about mycorrhizae, you should read this article].
- Defence against predators
- The root system
- Adaptations to soil composition
- Use of floors
- Use of water and other resources
2. Feed soil microorganisms: Soil fertility is proportional to the amount of soil microorganisms living in the soil. [If you want to know more about the role of soil microorganisms on its fertility, you should read the next post here]. We feed soil microorganisms by copying what happen in Nature,it means applyinng a layer of vegetal matter at the surface of the soil (= mulching).
3. Protecting the habitat of soil micro-organisms: Knowing the importance of micro-organisms for the good health, structure and fertility of the soil, it makes sense to us, at La Evidencia, to protect them and offer them shelter from the sun’s rays. In this idea, we will always make sure to leave a thick layer of organic matter on the ground.
4. By mixing biochar with soil, micro-organisms can colonize its pores and provide even more habitat. More available habitat means more biodiversity and, as a result, more opportunity for a healthy balance between prey-predators-pathogens and greater soil fertility. [If you want to know more about biochar, read the previous article here]
5. Control unwanted organism by providing habitat to their predators: The highest is biodiversity in our gardens, the highest the presence of the predators is possible. That will help to reduce the undesirable populations at a low enough level to inflict minimal damage to the harvest. Laying piles of stones in Mandala Gardens will allow hunters of insects and small rodents, such as amphibians or small reptiles to hide and take up residence there.
At La Evidencia, we decided to surround the two Mandala gardens with water. The reasons for a water basin placed at the delimitation of the vegetable gardens are:
- Attract birds and amphibians to feed on unwanted flying and running insects in gardens
- Create a suitable place for ducks to feed on snails, slugs or other animals whose presence in the vegetable garden is not always appreciated. Ducks are more suitable in a vegetable garden than chicken because they do not feed on plants and, unlike chicken, do not scrape the ground when they feed. In addition, duck feces are very fertile.
- Protecting plants from stress: In the wild, we can observe that plants grow more abundantly near freshwater sources such as rivers or lakes, thus avoiding the stress of lack of water. By enclosing gardens with a source of water that will constantly bring moisture to the ground, our goal is to copy the proximity of water that is required by plants to thrive in the wild. Conceive in such a way this space, as in natural conditions, plants should not need watering as long as the water is brought to them by the rains and made accessible by the proximity of the water resource and the porosity of the soil (which is kept porous by the abundance of micro-organisms and the presence of biochar) which allows rainwater to seep into the roots.
Sunlight is essential for photosynthesis to take place in plants but high temperatures reduce their performance in producing hydro-carbons by fixing CO2, and may even jeopardize their survival. [If you want to know more about photosynthesis and adaptation of warm country plants, you should read the next post on the Milpa here] This is why trees will also be planted in the Mandala gardens of La Evidencia in order to bring some shade to the plants. These trees will be of the Fabaceae family since a symbiosis between the roots of the plants of this family and a bacterium capable of fixing nitrogen from the air makes each part of the plant very rich in nitrogen. [If you want to know more about the symbiosis of Fabaceae allowing them to fix nitrogen, you should read the next here] Regular pruning of these Fabaceae trees with the deposition of pruning residues on the soil will ensure: - Constant fertilization of the Mandala Gardens - Permanent cover on the ground - Regular feeding of soil microorganisms - That the shade of plants is always light
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