It depends entirely on whether the tree grows to crop in an annual or a perennial setting. I will comment only on a perpetual agroforestry system involving moringa. Tropical plants usually have a problem. The soil is so thin in tropical environments that any significant disturbance will erode the topsoil. Why? Prodigious rainwater leaches all the nutrients into the subsoil or sends them off the land in runoff or into aquifers. To keep up with so much rainfall, a farmer would need to either use a ton of very slow release chemical fertilizers or come up with other strategies to fertilize the plant. Therefore, I will talk about some different procedures available in a Moringa agroforestry planting.
Strategies Available In Moringa Planting
Firstly, the best fertilization for a tropical plant is to deepen the topsoil. With all the rainfall in tropical environments, how can this be done? If you merely add topsoil or organic matter, it will go in a year. You need something that lasts a lot longer. I think biochar fits the bill. Biochar is pyrolyzed wood that has soaked in nitrogen-rich liquid (urine with water will do the trick). While it absorbs, it colonizes by beneficial bacteria, archaea, flagellates, and fungus. Adding a little topsoil or vermicompost will inoculate the biochar perfectly. The charred part of the biochar is the same as the material in a carbon filter. When that carbon filter is in saturation with nitrogen-rich molecules, it takes in these molecules from bacteria lifecycles, while giving these molecules to fungus, which in turn are attached to plant roots and provide the plant roots the necessary bits in exchange for sugars produced by photosynthesis.
In the Amazon, biochar is the most critical component of terra preta, the few sections of human-made soil in the Amazon found around historical villages and evidenced by increased growth of the forest. The way new terra preta archaeological sites came into existence is by satellites comparing the lush growth in terra preta soils to the healthy growth of the rest of the forest. These soils were amended with biochar 500 years ago or more, and yet the wood continues to flourish. Shouldn’t the biochar be buried 500 years deep in geologic time? Yes, it should. Why is it not? The Terra Preta soils are self-regenerating. So, the carbon in the leaf and fallen tree material and animal dung falls on top of a layer of Terra Preta. It is somehow ‘fixed’ by the terra preta (perhaps by an as yet unknown microbe that colonizes biochar then expands its realm by fixing more carbon), and enriches the soil. Biochar is in every hole where Moringa is in the plantation process and will help to keep the tree healthy and fertilized.