Organic Matter Decomposition In Coffee Plantations
Coffee Plantation soils in India are rich in organic matter, which in itself is a great strength for the sustainability of the plantations. However, due to continuous cultivation, the organic matter content of the soil decreases. Hence, the need to replenish the soil with organic matter. Organic matter decomposition serves two important functions, namely supply of energy to the biotic community and secondly, supply of carbon, which is the single most important element of all living beings.
Soil organic matter varies from soil to soil. In cultivated soils it is in the range of 1 to 15%., peat soils 90 to 100%. In tropical soils the soil organic matter content is high due to the fact that decomposition of organic residues is more rapid in warm regions. Coffee soils have more organic matter on the surface and gradually get lesser and lesser in the lower layers. However, one must bear in mind that the rich organic matter content in the soils was a result of a slow and deliberate process, over thousands of years where in the leaf litter, wood wastes, wild berries, animal droppings , subterranean portions of weeds and shrubs , above ground tissues, animal tissues got mixed up in the forest floor bed and slowly by the action of microorganisms converted it into precious organic matter and HUMUS. The major group of organisms taking part in organic matter decomposition are bacteria, fungi, actinomycetes and protozoa. The minor group includes earthworms, termites and insects.
A macro perspective of the coffee plantations is necessary to understand the rapid accumulation of organic matter. Firstly, Indian coffee plantations belong to a select few in the entire world, where coffee is grown under the canopy of a three tiered shade system. Secondly, the entire coffee is grown along with multiple crops. These two intrinsic factors literally translate into the setting up of BIOLOGICAL FACTORIES where tons of biomass in the form of leaf litter, wood shavings, and animal droppings get incorporated into the soil from time to time. Animal wastes (cattle / sheep/poultry, piggery) and coffee husk are also constantly incorporated into the soil and then get converted into available nutrients for plant growth and development. This ongoing process not only maintains soil fertility, but also enhances it. Leaf shedding is a very important biological process and on an average an Arabica plantation has close to 250 trees per hectare. So one can just imagine the amount of biomass incorporated into the dynamic soil day in and day out. Moreover, since the plantation comprises of various tree species, it acts as a fertile ground for the activity for soil organic matter decomposition.
However, the process of O.M.D. is not as simple as it seems. It is a fairly complicated process and to understand it one needs to look into the make up of soil organic matter. It is a step by step process.
Firstly, organic matter consists of residues of plants and animals at various stages of decomposition and essentially mediated by soil micro flora. The biological transformations taking place result in various products at different stages, ultimately leading to the formation of rich ORGANIC MATTER and HUMUS inside the plantation. Dead and decaying animal and vegetative matter are periodically recycled into the coffee soils. Macro organisms like insect and worm castings also get incorporated after their respective life cycles. Billions of microbial cells , namely fungal mycelium, viral capsules, bacterial and actinomycetes cells which have a very short generation time build up a strong reservoir of nutrients for microbial succession to act upon the organic matter. In addition to this planters have mastered the art of composting farm wastes, green manures, bio slurry and recycling it into the plantation there by accelerating the entire process of organic matter production. The coffee plantation itself acts as a huge COMPOST PIT and a perfect zone for formation of organic matter because of the heterogeneous mixtures available within the plantation. The soil itself is a microcosm. It harbors a wide variety of microorganisms that attack, decompose and assimilate every known type of substance. The changes taking place are numerous and complex.
An understanding of the intrinsic composition of organic residues helps in deciphering the entire process of soil organic matter accumulation. Soil organic matter consists of 2 main groups of compounds
B) No nitrogenous.
Nitrogenous compounds contain chiefly proteins and nitrogen bases. Where as the no nitrogenous group contains carbohydrates, lignin's, tannins, organic acids, ash, mineral matter, water, phosphates, sulphates, calcium, magnesium, sodium, potassium, iron, zinc, copper, manganese, boron etc. The entire make up of this organic complex consists of substances of widely different chemical composition. This acts as a precursor in the breakdown of the complex both by macro and microorganisms.
The entire process is evolutionary in nature. As a first step the animal and plant residues are subjected to microbial attack. In the second step, rapid multiplication of microorganisms results in the increase of enzymatic activity and builds up of biomass. Lastly, the production and accumulation of end products needed for plant growth and development takes place. The simple constituents are assimilated directly by the microorganisms, part of the carbon is utilized for synthesizing the microbial tissue and the rest is oxidized and eliminated as carbon dioxide. This in turn is used for photosynthesis by plants and trees. However the crucial parameters for soil organic matter decomposition are optimum temperature, Moisture, hydrogen ion concentration, and aeration.
An area of main concern over the years has been regarding the INSOLUBLE COMPLEX of soil organic matter. This complex consists of cellulose, hemicelluloses, lignin proteins, starch, gum, mucilage, fats and pectic substances.
Cellulose: is the most abundant carbohydrate present in plant residues. It forms 10 to 20% dry matter of young plant materials and 20 to 40% of mature materials like straw, stalks and stubbles. It is important to note that only a few specific fungi, actinomycetes and bacteria are alone capable of decomposing cellulose. During the process of decomposition the decaying material changes its color to dark brown. This in turn is due to the production of dark colored pigments produced by cellulose decomposing microorganisms resulting in the black color of humus.
Hemicelluloses are an essential component of plant cell wall. It also acts as a reservoir of carbohydrates in seeds and constitutes 5 to 10 % of dry matter of young plant material and 15 to 30 % of mature plant tissue. Microorganisms are capable of breaking hemicelluloses into simpler substances and make it available to the plant for uptake by the root system.
Lignin: 10 to 30% of the dry matter of mature plant material consists of lignin. It is an important constituent in providing strength to the skeletal frame work of the plant. Termites are capable of breaking this tough material into readily absorbable forms.
Proteins: consist of 1 to 25 % of dry matter. Young and tender plants, weeds, contain a high proportion of protein. All types of soil microorganisms are able to bring about the decomposition of proteins.
HUMUS: A very important component of organic matter decomposition is humus. Its physical and chemical properties though not fully understood, it plays a pivotal role in maintaining the fertility status of plantation soils. It consists of a lingo protein complex containing 45% lignin compounds, 35% amino acids, 11% carbohydrates, 4% cellulose, 7% hemicelluloses, 3 % fats, waxes & resins and 6 % other plant inhibitors and growth promoting substances.
The dark brown to black color of surface soils is due to the presence of humus. It is the core element in organic matter and provides the dynamic equilibrium to the entire coffee soil system. Humus has great water absorbing and water holding capacity. 100 parts by weight absorb nearly 180 parts of water against 70 for clay and 25 for sand. Humus possesses the power of adhesion and cohesion and acts as a cementing agent as well as a binding agent. It has a high ion adsorbing capacity and is also insoluble in water. It acts as a buffering agent and there by prevents sudden changes in soil reaction. Provides vital nutrients to coffee plants and acts as an energy source for proliferation of microorganisms. It is comparatively resistant to microbial attack, yet undergoes slow decomposition. Physically, humus modifies soil color, texture, structure and water holding capacity. Improves aeration and drainage by making soil more porous. It takes thousands of years for the formation of humus and in essence is the key to the production of quality coffee.
Soil organic matter is an excellent conditioner for coffee plant rejuvenation and to a great extent responsible in controlling the relationship between a healthy soil and healthy plant. One must bear in mind that as cultivation progresses, the organic matter of the soil decreases. Hence, adequate steps should be taken to compliment the organic matter status of the soil by way of incorporating crop residues from time to time.
The base required for preparation of Chemical fertilizers is nonrenewable fossil fuels. India is a net importer of naphtha that goes into the manufacture of the bulk of fertilizer nitrogen, namely urea and diammonium phosphate. Most of the organic matter in soils has an appreciable amount of nitrogen which is taken up by the plants according to various growth stages. Also chemical fertilizers are sensitive to high temperature and moisture and are lost by way of leaching or volatilization. Rarely does one see ideal conditions in the field to apply fertilizer. On the contrary, organic matter can withstand a wide degree of soil temperature and moisture variation and rarely are the nutrients lost. Looking deeply, soil organic matter along with composts is a hygienic model of disposing organic wastes which would otherwise cause pollution problems. It also creates wealth from waste. Indian planters are by and large small farmers with holding of less than 10 hectares of land. In such a scenario, their purchasing power is weak and organic composts help in meeting their fertilizer requirements.
The coffee bush, annually, removes large quantities of nutrients from the soil. The bulk of the nutrients go into the preparation of so called WOODS, which bear the coming year's crop. In simple terms the coffee plant has a BIOLOGICAL CLOCK within, which in turn programmes the plant almost one year in advance as to where the respective photosyntahtes should be Tran located to produce fruits, leaves, productive woods, shoots and other material. This requires a constant supply of Macro as well as Micro nutrients in addition to growth promoting substances. The rich organic matter and humus provides the ideal set up for plant programming.
It is an established norm worldwide that shade grown coffees are the best because of the uniform maturity of sugars inside the fruit. In addition to this the high levels of soil organic matter aid in the balanced nutrition wherein the end product, namely the fruit gets a balanced taste , hence Indian coffee is much sort out by foreigners to get a good blend.
In an era where chemical or synthetic fertilizers are given prominence, the side effects are many. They leave behind a trail of destruction. These chemicals not only pollute groundwater but are a cause for many present day diseases. Mankind is slowly loosing his resistance or immunity due to intake of synthetic fertilizer food .Chemicals are quick to act but they leave behind a trail of poisons in the soil. The very future of farming is affected. Hence the need to build up soil organic matter which not only reduces the dependency on chemical fertilizers, but also enriches the fertility status of the soil without any side effects. Soil organic matter improves root growth, uptake of minerals and aids the plant in a host of physiological activities. It increases mobilization of nutrients both major and minor from the soil. It also produces growth promoting substances and higher nitrogen fixation by bacteria. It is also essential in the formation of soil aggregates and soil structure which has a direct bearing on soil aeration. Antibiotics are also produced keeping in check soil borne pathogens. Acids released, dissolve insoluble phosphates and make it available.
Exploitation of coffee soils is the order of the day. In reality excessive use of fertilizers renders the soil SICK. The best way to go about this is converting organic residues into energy rich nutrients. This goes a big way in protecting the future and stabilizing the land. As days goes by there are no soft options left. In the race for preserving planet earth the farming community throughout the world has to work together for common good of mankind. After all, human beings have only one world to live in and that is MOTHER EARTH.
Published: December 2003, Last Modified: September 2011