Feeding the Soil - Part 4

by Richard Chew

After my previous improvements as posted in Feeding the Soil - Part 3, there is marked improvement, but I was still not very satisfied with the rate of decomposition.

Upon learning that peat moss helps decrease pH of soil and also increase rate of decomposition of organic matter, I decided to add peat moss as top soil. Peat moss has carbon nitrogen ratio of 50:1. And it has higher population of actinomycete bacteria that is responsible to decompose organic matter. This decomposition process is also known as mineralization of organic matter that converts organic matter into non-organic ammonia mineral. Subsequently ammonia is used by other bacterias for their metabolic activities, also known as nitrogen fixing. During the metabolic activities, these bacteria will respire nitrogen into a form that can be taken in by plant roots as nutrients.

The peat moss also aids in decomposing dry fertilizer (pellets form - chicken and sheep manure), including those that are highly processed which are harder to decompose. Mixing dry fertilizer with the peat moss, will help to break down the fertilizer more easily thus faster release of needed nutrients into the soil. Without peat moss (or any substance that aids decomposition), the bacteria may draw nitrogen from the soil to break down the fertilizer. This is the reason why the dosage of fertilizer must correspond with the size and health of the plant. Otherwise both the fertilizer and the plant roots would be competing for the same source of nitrogen. To build on that, if the plant roots are not healthy, the same bacteria that decompose the organic matter may choose to 'attack' the roots instead because the unhealthy roots become easier to break down.

However peat moss need to be mixed with other low carbon nitrogen ratio matter to create a better soil metabolic effect. Peat moss by itself, tends to retain too much moisture and may invite more fungal decomposition. Its surface tends to be grayish (sign of fungal). Of course retaining moisture has it benefits, but if too much may tightened the top soil that impedes aeration especially after heavy rain fall. Too high moisture content will lead to anaerobic fermentation, because the soil structure lacks access to O2 thus will increase the soil pH (alkaline soil). This probably explains the cause of chlorosis at my Nozomi rose which is sign of suffering from the inability to absorb iron. More about my experience in countering chlorosis in my next posting.

Having mentioned the above I need to clarify that the grayish texture at the peat moss surface is not a bad sign. It actually confirms the presence of actinomycete, a kind of fungal bacteria (because it is fillimous, and has spores) for decomposing organic matter. If its high with actinomycete, don't be surprise a mushroom may suddenly spring up from the soil in the early morning.

To prevent or to minimise anaerobic fermentation (that will increase soil pH), we need to add material that provide good top soil structure for better aeration to aid aerobic decomposition. And it should contain low carbon so that metabolic activities can be raised without depleting nitrogen at the top soil.

I used grass cuttings. It is inexpensive. It cost about RM2.60 per pack. It has the right carbon nitrogen ratio (20:1), that utilises nitrogen from its own source when decomposing. And its structure goes well with peat moss to improve top soil aeration. I would mix about 50% (of volume, not weight) with the peat moss. I noticed a dramatic difference in the soil structure after mixing it with grass cuttings.

The top soil becomes less tight, much softer and more fluffier (better aeration). I noticed it becomes brownier (and less grayish) when I turn over the top soil on the following day This is good sign of good compost soil.

I have just pruned my Portmeirion rose. I did the top soil as mentioned above. Hopefully by Dec I will get good display of flower. The rose is responding well with some buds at the main stem. Hope to get about 10 strong shoots for flowering.

Aerobic Decomposition [EXT]

I extracted this resouce from http://whatcom.wsu.edu/ag/compost/fundamentals/biology_aerobic.htm

This resource explains on the aerobic decomposition and the necessity for soil to be aerated and sufficient low carbon nitrogen ratio material to aid decomposition.

Organic material decomposing with oxygen is an "aerobic" process. When living organisms that use oxygen feed upon organic matter, they develop cell protoplasm from the nitrogen, phosphorus, some of the carbon, and other required nutrients. Carbon serves as a source of energy for organisms and is burned up and respired as carbon dioxide (CO2). Since carbon serves both as a source of energy and as an element in the cell protoplasm, much more carbon than nitrogen is needed. Generally, organisms respire about two-thirds of the carbon they consume as CO2, while the other third is combined with nitrogen in the living cells.

Biological activity diminishes if the compost mix contains too much carbon in relation to nitrogen. Several cycles of organisms are required to burn excess carbon. This is a complex chemical process. When organisms die, their stored nitrogen and carbon become available to other organisms. These new organisms form new cells which again need nitrogen to burn excess carbon and produce CO2. Thus, the amount of carbon is reduced and the limited amount of nitrogen is recycled. Finally, when the ratio of available carbon to available nitrogen is low enough, nitrogen is released as ammonia. Under favorable conditions, some ammonia may oxidize to nitrates. Phosphorus, potash, and various micronutrients are also essential for biological growth. These are normally present in more than adequate amounts in compostable materials.

In nature, the aerobic process is most common in areas such as the forest floor, where droppings from trees and animals are converted into relatively stable organic matter. This decomposition doesn’t smell when adequate oxygen is present. We can try to imitate these natural systems when we plan and maintain our landscapes. As we learn more about the biology and chemistry of composting, we can actually hasten the decomposition process.

When carbon is oxidized to CO2, a great deal of energy is released as heat. For example, if a gram of glucose molecules is dissimilated under aerobic conditions, 484 to 674 kilogram calories (kcal) of heat may be released. If organic material is in a large enough pile or arranged to provide some insulation, temperatures during decomposition may rise to over 170° F. At temperatures above 160° F, however, the bacterial activity decreases.

There are many different kinds of bacteria at work in the compost pile. Each type needs specific conditions and the right kind of organic material. Some bacteria can even decompose organic material at temperatures below freezing. These are called psychrophilic bacteria, and although they work best at around 55°, they continue to work down to 0° F. As they work, they give off small amounts of heat. If conditions are right, this heat will be enough to set the stage for the next group of bacteria, the “mesophylic,” or middle range temperature bacteria.

Mesophylic bacteria thrive from 70° to 90° F, but just survive at temperatures above and below (40° to 70° F, and 90° to 110° F) In many backyard piles, these mid range bacteria do most of the work. However, if conditions are right, they produce enough heat to activate the “thermophilic,” or heat loving bacteria. Thermophilic bacteria work fast. Their optimum temperature range is from 104° to 160° F.

High temperatures destroy pathogenic bacteria and protozoa (microscopic one celled animals), and weed seeds, which are detrimental to health and agriculture when the final compost is used on the land.

Aerobic oxidation does not stink. If odors are present, either the process is not entirely aerobic or there are materials present, arising from other sources than the oxidation, which have an odor. Aerobic decomposition or composting can be accomplished in pits, bins, stacks, or piles, if adequate oxygen is provided. To maintain aerobic conditions, it is necessary to add oxygen by turning the pile occasionally or by some other method.