Soil organic matter concentration is among the most important indicators of soil fertility. Soil fertility is mainly dependent on the extent of organic matter in the soil. Organic matter being the most dynamic fraction of soil has its specific role in improving soil structure, water holding capacity of the soil, nutrient retention capability of the soil, biological nitrogen fixation, soil aeration, root penetration, nutrient availability to plants, soil conservation by providing sticking power to soil separates, imparting suitable tilth to soil, supporting micro flora and micro fauna in the soil and maintaining buffering and exchange capacity of the soil.
Keeping in view the significance of organic matter in soil productivity, it is imperative to maintain its high reserves in our soils. However, intensive agriculture in response to soaring food needs is one reason for decline in soil organic matter. Buildup of soil organic matter under climatic conditions characterized with high temperature, low rainfall and alkaline pH is highly difficult due to high decomposition rates. On the other hand, increased demands for food to nourish billions of people in the world led the growers for intensive cultivation and huge fertilizer inputs without concerning the soil sustainability, which resulted in problems like nutrient imbalance, microelements deficiency, soil erosion, reduced microbial activities, reduced nutritional value of food, low farm productivity, burning of soil, inefficiency of fertilizer, and ultimately the stagnant yields. All these problems, in one or the other way are related to swift degradation of organic matter in our soils and can be considerably managed if the organic matter is sustained on long term basis even at its present magnitude.
Recycling of nutrients is the basic as well as vital feature of sustainable soil management. Importantly, it is the approach to build organic matter contents in the soils. In fact the plant remains are biodegradable. All nutrients removed from the soil by crop plants are stored in the crop herbage and grains along with the sun energy embodied in the form of different compounds.
One way to recycle the plant nutrients is to incorporate crop residues into soil where they will become a part of soil after decomposition while the other one is to use animal dung and farm wastes for the same purpose. Moreover the domestic and industrial wastes of organic origin can return immense nutrients to an agricultural system.
In many parts of the world, 8 to 40 percent (or even more) of the crop residues are left on soil after crop harvest which can be incorporated to enrich soil with organic matter and plant nutrients. Although wheat, rice, and maize vegetative parts are mostly utilized to feed livestock, however, not only a considerable part of them is left in the field but also a specified amount of wheat and rice straw can be left in the field when harvested with combine harvester which is capable of cutting the crop at desired height. Also in case of cotton, the sticks can be rotavated to act as manure. One to half bag of urea per acre depending on the amount of plant residues can be mixed into soil to fasten the decomposition process.
Soil organisms such as termites and earthworms start decomposing plant residues to convert them to tiny pieces when added to soil. The residues, now in smaller size, are further subjected to action of other microorganisms to degrade micro molecules as starches, amino acids, proteins, sugars etc. while the macro molecules as fats, waxes, liginin etc., are first converted to simpler compounds for further breakdown. Liginin containing residues require more time to decompose. Microorganisms release certain enzymes to accomplish the decomposition process. Finally the residues are converted to CO2 which is utilizes by soil microbes as energy source and become their body part and humus, the stable organic matter, which becomes lasting part of soil.
Animal dung is being used as manure for centuries. Nor all the organic matter present in the forage is digested by animals rather only 50 percent of it is utilized. Incorporation of fresh animal manure into soil and just prior to sowing is not recommended due to energy and time required for it biodegradation. It results in weak crop stand and poor crop quality. Moreover fresh animal manure may contain weed seeds and disease pathogens which are desired to be destroyed.
Composting of the animal manure, a very simple but time consuming process, is the pertinent solution to these problems. The animal dung mixed with the farm wastes is deposited into a trench for 3 to 5 months to convert it to well rotten blackish brown colored compost. The size of the trench depends on the number of animals. For instance, a trench with 1 meter depth and 7 meter length can sufficiently store excreta of 5 to 6 animals.
Bacteria, fungi and certain other microbes decompose animal excreta and the farm wastes to finally change it to dark brown material called humus, which ultimately acts as the stable fraction of soil. The gases like methane, ammonia, carbon dioxide hydrogen produced from the process can serve the additional purpose of energy generation after installment of especially designed appliances.
Optimum range of factors like moisture, temperature, pH etc., is highly crucial for completion of composting process. A moisture percentage of 50-60, high temperature i.e., above 35◦C, and acidic pH make the process fast and convenient. Turning upside down the materials fastens the compost formation.
Compost contains a wide range of plant nutrients including micro as well as macro elements, and can be used to nourish crops, vegetables, flowers and fruits at 15 to 20 carts per acre. A typical compost sample may have 1.34 percent N, 1.3 percent P, 1 percent K , 0.89 percent Ca and also the other elements in small fractions.
If we keep continued destroying our soils in the same fashion of carelessness, the fertile lands will soon become barren. It is need of the time to aware our farmers about the necessity of conserving the soil through nutrient recycling phenomenon. There is need to aware the farmers about the benefits of incorporating the plant residues into soil rather than their feeding to animals (or burning in some parts of the world), and teach them techniques for animal excreta preservation, compost formation and its application in the field.