Composting in Natural Silviculture

by Dexter B. Dombro

Bags of chicken manure for composting.

When you have over one million tropical trees planted in poor soil, fertilizing them becomes a major task. This task is even more complicated when you don’t use agrochemicals as a quick fertilizer solution. At La Pedregoza we are using completely organic processes, starting in the tree nursery, through planting to ongoing maintenance of the trees in their cultivations. Organic processes and natural silviculture practices are very labour intensive, but amazingly still cheaper than the cost of purchasing agrochemicals and then applying them. This article details some of the things we do to fertilize our trees in a sustainable manner.

First, let me briefly explain the critical reasons why we use organic processes at La Pedregoza:

Agrochemicals are not friendly.

a.       Agrochemicals kill the microfauna in the soil, leading to dead soil;

b.      Dead soil means more risk of diseases and plagues, as the immune systems of the trees are compromised;

c.       Dead soil also means an assault on nature, because healthy soils are the foundation of biodiversity;

d.      Agrochemicals compact the soil, while organic fertilizers allow aeration, nutrient  and humidity retention in the soil;

e.      Agrochemicals can burn tree roots and need other additives like dolomitic lime to deal with soil acidity;

f.        Soils with organic material in them are naturally less acidic;

g.      The use of agrochemicals over long periods is not sustainable from either a financial or an environmental point of view. 

Making pooballs at La Pedregoza

In previous articles I discussed some of the natural fertilizers we make at La Pedregoza, using Cebu cow manure, like for example Jivamritham. However, the role of those fertilizers, while they do have a nutritional value, is mainly to spread efficient micro-organisms in the soil for a better conversion of other organic materials into nutrients, like dead twigs, branches, fallen leaves and the like. Tropical trees get 98 percent of their requirements from the atmosphere and from rainfall, but it is the missing 2 percent that can be critical to the tree’s growth. When soils are very poor, which is common in tropical settings, foresters have to find a way of providing the missing elements. While agrochemicals tend to be very condensed, natural fertilizers tend to be bulkier, requiring the application of larger quantities per tree.

Turning compost is a hated activity.

At La Pedregoza we require 1,200 metric tons of organic fertilizer per year, not only to feed the trees, but also to slowly build up the soil, while improving the soil’s microfauna. This quantity allows us to apply 1 kilogram (2.2 lbs) of organic fertilizer to each plantation tree, and 3 kilograms of organic fertilizer to each producing fruit tree (for example, cashews, mangoes, tamarinds, citrus and rubber trees). This is obviously a huge amount of organic material, so how do we produce it and what are some of the issues?

Grass collected and added to compost.

The obvious solution is to produce compost. A reasonable definition of compost is that it’s a mixture that consists mostly of decayed organic material and which is used to fertilize and condition soil. While natural decomposition in nature will produce a compost-like material over a period of years, human activity seeks to create a blend that has a better distribution of nutrients and essential elements, while also accelerating the natural decomposition process so that it only takes a few months. At La Pedregoza we start with Cebu cow manure we collect in our stable, or that we get donated from neighboring ranches. Next we cut large quantities of grass in the savannah, letting some dry to become hay, while some we add fresh for improved nitrogen content. Finally, we also chip and add wood and brush pieces collected from pruning trees, or we add biomass from other crop residues, like sugar cane, maize or African hibiscus, which are all annuals.

Chipping and shredding biomass for compost.

All of this is mixed together and may include chicken manure, kitchen scraps, old newspapers and cardboard boxes shredded, as well as a little bit of ordinary soil so that local microfauna can go to work in the compost pile. We generally aim to maintain compost piles that have approximately 50 metric tons of organic material each, with 4 piles cooking at any given period of time, so that we have some 200 metric tons available for use every 2 months. At La Pedregoza the various piles are distributed all over the plantation, to minimize internal transportation costs and to increase efficiency by minimizing the distance from each pile to the destination trees.

Cheap solution for aerating compost piles.

The task most hated about compost is turning the pile, supposedly for the purpose of aeration. The idea is that the microfauna doing the decay will be more efficient when aerated. When talking about piles that are 50 tons each, this becomes a labor intensive nightmare, with several workers and the tractor taking an entire day or more to shift the pile, made worse when the turning is something one does every 10 days. However, at La Pedregoza we have developed an alternative methodology, which involves running a 6” (15 cm) diameter PVC pipe filled with holes down the center of the pile, together with some 1.5” diameter PVC pipes that connect like a porcupine to the larger pipe, allowing air to circulate throughout the pile. Research on the subject has revealed that turning the pile results in aeration that only lasts 15 minutes, so it is questionable as to whether the cost of turning is justified.  In our opinion, it is better to take a lazy approach without turning and to wait a little longer than normal for the compost to be ready.

Loading compost trailer with small tractor.

The next challenge is how to apply the compost to the trees. With younger trees the solution at La Pedregoza is to use a small 23 HP tractor towing a light trailer through the cultivations. This is important, because too much weight can compact the soil and hurt the roots of the trees. The small tractor and trailer have little impact, so it is an efficient solution. While one worker drives the tractor through the cultivation, two others follow and deposit a shovel-full of compost to each tree, one worker on the left and the other on the right. Using this methodology several hundred trees can be fertilized in rapid succession. A shovel full of compost is approximately 1 kilogram and is deposited close to the tree’s trunk. Fertilizing is done during the rainy season to minimize sun damage and to allow the nutrients to seep down around the roots.

Mid-point hole made with auger for compost.

With older trees we use small, hand-held augers that have a gasoline engine. A hole some 20 cm (8”) in diameter and 20 cm (8”) deep is made at the mid-point between trees in the cultivation. This is also the outer point to which each tree’s roots extend. The roots can smell the fertilizer and will grow into the area with the compost-filled hole. Once the hole is made with the auger and filed with a shovel full of compost, the soil is deposited back on top of the hole. Unfortunately, this is a more labour intensive approach, so at La Pedregoza we are also exploring whether depositing compost around the trunk area is less or equally efficient for fertilization purposes.

Applying shovels full of compost to each tree.

One issue in the tropics with compost is having mushrooms or ants invade the compost. Mushrooms may offer direct competition to the tree, so they are undesirable, while ants may cause other problems. Both of these issues are often the result of incomplete composting and too much humidity in the compost. In the event the problem seems to be out of control, the best solution is to add dolomitic lime to the compost after it has finished cooking. The lime discourages the ants and the mushrooms. However, it does require that the compost is then left for 14 days before being used, so that the lime is well blended and can no longer affect the tree roots directly or harm the soil microfauna. Since the aim of the compost is nutrition, using the dolomitic lime is not a bad thing, since it is a natural substance that does supply calcium to the trees. The other alternative is to use wood ashes, when available.

Hopefully this article will demystify some of the issues around big natural silviculture projects. It doesn´t mean we have all of the answers, but at La Pedregoza we are well on our way to solving large scale tropical forestry issues with practical, local solutions. Part of being natural and organic is trying to reduce the amount of materials transported over large distances; our aim is to procure everything we need from within a 50 mile (80 km) radius of the plantation. La Pedregoza and its Sacred Seeds Botanical Garden have been Tree-Nation projects for some time, and using sustainable, environmentally friendly practices is a big part of our commitment as a Tree-Nation plantation.